Lipomatous hemangiopericytoma: a rare variant of hemangiopericytoma that may be confused with liposarcoma

Intermediate metastatic risk lipomatous solitary fibrous tumor of the thigh (previously known as hemangiopericytoma): A rare case report with a literature review

RATIONALE

Solitary fibrous tumor (SFT) is a rare mesenchymal tumor, which can arise at any anatomical location and exhibit a wide variety of histopathological characteristics. Lipomatous solitary fibrous tumor (LSFT) is a rare variant of SFT characterized by hemangiopericytoma-like vascular areas with a varying amount of adipocytic tissue. LSFT can be misdiagnosed with other tumors such as liposarcoma which can lead to unnecessary overtreatment for patients.

PATIENT CONCERNS

A 48-year-old man presented to the hospital clinic with a painless swelling located on the medial area of the upper thigh near the femoral artery, he has not seen any change in its size since he has noticed it a year ago.

DIAGNOSES

Histological examination confirmed LSFT with an intermediate risk of metastasis.

INTERVENTIONS

Three-dimensional imaging technology with intravenous injection of contrast material was made and revealed a mass with well-vascularity supplied from the deep femoral artery. The lesion was excised and showed an intramuscular well-circumscribed encapsulated mass.

OUTCOMES

The pathological findings LSFT with intermediate metastatic risk, and he is scheduled to receive radiotherapy for one and a half months. The majority of SFTs display benign histological characteristics and typically follow a slow clinical progression, leading to a favorable prognosis. To date, fewer than 20 cases of malignant LSFT have been documented. In our case, we utilized a recent tumor classification model that evaluates the metastatic potential of SFTs, and long-term follow-up is necessary because there is a chance of aggressive behavior.

LESSONS

LSFTs are usually found incidentally and often present as painless, movable masses. Even though they mostly follow a benign course, long-term follow-up is essential due to the possibility of turning malignant.

A case of fat-forming solitary fibrous tumor that is prone to be confused with liposarcoma

Fat-forming solitary fibrous tumor is a rare and specific subtype of solitary fibrous tumor. In this case, a mass of 8.3 cm in diameter was found in a 59-year-old male patient's right retroperitoneum, as revealed by abdominal contrast-enhanced computed tomography (CT) images. The tumor exhibited a well-circumscribed nature and histological features characterized by a combination of hemangiopericytomatous vasculature and mature adipose tissue, comprising around 70% of the total tumor composition. Immunohistochemistry staining revealed diffuse positive expression of STAT6 and CD34 in the tumor cells. Based on these findings, the final diagnosis was determined to be a fat-forming solitary fibrous tumor located in the retroperitoneum. It is important to consider other potential differential diagnoses, including angiomyolipoma, dedifferentiated liposarcoma, spindle cell lipoma, and atypical lipomatous tumor/well-differentiated liposarcoma.

Imaging, pathology, and diagnosis of solitary fibrous tumor of the pancreas: A case report and review of literature

BACKGROUND

A solitary fibrous tumor (SFT) is often located in the pleura, while SFT of the pancreas is extremely rare. Here, we report a case of SFT of the pancreas and discuss imaging, histopathology, and immunohistochemistry for accurate diagnosis and treatment.

CASE SUMMARY

A 54-year-old man presented to our hospital with pancreatic occupancy for over a month. There were no previous complaints of discomfort. His blood pressure was normal. Blood glucose, tumor markers, and enhanced computed tomography (CT) suggested a malignant tumor. Because the CT appearance of pancreatic cancer varies, we could not confirm the diagnosis; therefore, we performed endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB). Pathology and immunohistochemistry were consistent with SFT of the pancreas. The postoperative pathology and immunohistochemistry were consistent with the puncture results. The patient presented for a follow-up examination one month after discharge with no adverse effects.

CONCLUSION

Other diseases must be excluded in patients with a pancreatic mass that cannot be diagnosed. CT and pathological histology have diagnostic value for pancreatic tumors. Endoscopic puncture biopsy under ultrasound can help diagnose pancreatic masses that cannot be diagnosed preoperatively. Surgery is an effective treatment for SFT of the pancreas; however, long-term follow-up is strongly recommended because of the possibility of malignant transformation of the tumor.

Solitary fibrous tumor: Can the new Huang risk stratification system for orbital tumors improve prognostic accuracy in other tumor locations?

Solitary fibrous tumors (SFTs) are known for their heterogeneous morphology, characterized by a variety of cell shapes and different growth patterns. They can also arise in various anatomical locations, most commonly in extremities and deep soft tissues. Despite this diversity in morphology and location, all SFTs share a common molecular signature involving the NAB2::STAT6 gene fusion. Due to their unpredictable clinical behavior, establishing prognostic factors is crucial. This study aims to evaluate an orbital risk stratification system (RSS) proposed by Huang et al. for use in extraorbital SFTs using a database of 97 cases. The Huang model takes into consideration tumor size, mitotic figures, Ki-67 index, and dominant constituent cell (DCC) as key variables. Survival analysis confirmed the model's predictive value, with higher-risk scores being associated with poorer outcomes. However, in contrast to the orbital SFTs studied by Huang et al., our study did not find a correlation between tumor size and recurrence in extraorbital cases. While the Huang model performs slightly better than other RSS, it falls short on achieving statistical significance in distinguishing recurrence risk groups in extraorbital locations. In conclusion, this study validates the Huang RSS for use in extraorbital SFTs and underscores the importance of considering DCC, mitotic count, and Ki-67 together. However, we found that including tumor size in this model did not improve prognostic significance in extraorbital SFTs. Despite the benefits of this additional RSS, vigilant monitoring remains essential, even in cases classified as low-risk due to the inherent unpredictability of SFT clinical outcomes.

Cytomorphological Spectrum of Solitary Fibrous Tumor: Revisited

BACKGROUND

Solitary fibrous tumor (SFT) is a tumor of mesenchymal origin. Its diagnosis on cytology is challenging, owing to variation in cellularity, sparsely distributed cellular and stromal components and inapparent vasculature. The cytomorphologic findings have been rarely described in literature with a few case reports and occasional case series. We present the cytomorphologic features of SFT with special emphasis on immunochemical findings.

MATERIALS AND METHODS

We present cytological data from eight cases of histopathologically proven SFTs. The cytomorphologic features, immunochemical markers and differential diagnostic entities on fine needle aspiration cytology (FNAC) arediscussed.

RESULTS

FNA was performed at different anatomical sites. Cytology smears showed variable cellularity with tumor cells arranged in loose clusters and as singly scattered cells. Interlacing fascicles with palisading of cells was noted. The cells were predominantly spindle to elongated, having moderate cytoplasm with elongated wavy nuclei. These nuclei had fine to coarse chromatin, with inconspicuous to prominent nucleoli. There was prominent metachromatically staining, amorphous to fibrillary, collagenous to myxoid matrix materialassociated with tumor cells. Other findings included intranuclear pseudo-inclusions, multinucleated giant cells and atypical mitoses. Cytological diagnosis offered varied from 'spindle cell neoplasm' to 'spindle cell sarcoma' or 'suggestive of sarcoma'.Immunocytochemistry (ICC) done on cell block sections showed positivity for STAT6, CD34 and Bcl-2.

CONCLUSION

Cytological diagnosis of SFT can be challenging. A prudent search for characteristic cytomorphological features is of diagnostic help. The cytomorphology should be interpreted with caution with appropriate ICC panel including STAT6 and CD34.

Toward Better Understanding and Management of Solitary Fibrous Tumor

Solitary fibrous tumor (SFT) comprises a histologic spectrum of soft tissue neoplasms that are characterized by the unique NAB2-STAT6 gene fusion. Changes in diagnostic terminology and site-specific classification over the past few decades have resulted in a disjointed literature. Complete surgical excision with preservation of function remains the mainstay of treatment. New risk stratification systems including risk factors such as mitotic rate, age, tumor size, and presence of necrosis, among others, can be used to predict risk of recurrence or metastasis. Long-term follow-up after surgical resection is recommended. The clinical manifestations, diagnosis, management, and prognosis of SFT are reviewed here.

[Fat-forming solitary fibrous tumor with NAB2/ STAT6 gene fusion. Case report of genial location and literature review]

The lipomatous variety solitary fibrous tumor is a soft tissue neoplasm composed of mature adipose tissue and hemangiopericytoma areas. A 53-year-old man consulted for facial asymmetry and maxillofacial magnetic resonance imaging showed a cystic lesion, 3 x 2 cm in size, in front of the anterior wall of the maxillary sinus. Histologically, there were dense spindle cells expressing CD34, CD99, Bcl-2, and STAT6, myxoid zones, hemangiopericytomatous blood vessels, and S100 positive adipocytes. NAB2/STAT6 gene fusion was revealed by RT-PCR. The main differential diagnosis was raised with the spindle cell lipoma and malignant variant of the lipomatous solitary fibrous tumor. STAT6 overexpression and NAB2/STAT6 gene fusion are specific for lipomatous solitary fibrous tumor and the presence of lipoblasts and atypical lipomatous tumor areas suggests malignancy. These tumors located in the head and neck region have a benign biological behavior.

Cytopathological characteristics of solitary fibrous tumour involving the pancreas by fine needle aspiration: Making an accurate preoperative diagnosis in an uncommon location

BACKGROUND

Solitary fibrous tumour (SFT) is a unique mesenchymal neoplasm with classic features on histology and is characterised by the NAB2-STAT6 gene fusion. There are rare reports of SFTs with pancreatic involvement and only two cases in the literature reporting its features by preoperative fine needle aspiration (FNA). Herein, we characterise the cytomorphological features of four SFTs involving the pancreas by FNA to establish a preoperative diagnostic approach.

METHODS

The anatomic pathology archives of two academic medical centres were searched to identify patients with a pancreatic FNA cytology specimen and a confirmed diagnosis of SFT by surgical resection. The clinical history, pathological diagnosis, cytomorphological findings, and results of immunohistochemistry (IHC) were reviewed.

RESULTS

Four SFTs were identified from four patients with a median age of 59 years. The morphological features were variable but most frequently showed a bland spindled-to-epithelioid proliferation in fragments and single cells with small, oval, elongated, and hypochromatic nuclei in a haphazard arrangement with or without dense collagen. One tumour presented with a concurrent metastasis and showed a pure epithelioid component with necrosis and enlarged, hyperchromatic nuclei with conspicuous nucleoli and scattered mitoses. IHC was necessary for all diagnoses which were confirmed by surgical resection.

CONCLUSIONS

SFTs with pancreatic involvement are rare, and non-specific features and tumour heterogeneity can pose a diagnostic challenge on FNA; however, IHC can be used to make a definitive diagnosis. As a result, FNA is a simple, safe, cost-effective, and accurate approach that can be used to diagnose SFT in the pancreas.

Solitary Fibrous Tumor: Integration of Clinical, Morphologic, Immunohistochemical and Molecular Findings in Risk Stratification and Classification May Better Predict Patient outcome

Although solitary fibrous tumors (SFTs) have an unpredictable evolution, some specific clinicopathologic factors have been associated with the final outcome. We retrieved clinical, pathological and molecular data of 97 patients with a histological diagnosis of SFT and Signal transducer and activator of transcription 6 (STAT6) positivity. We retrospectively studied the pathological factors predictive of recurrence/metastasis and compared them with the clinical outcome. A wide immunohistochemical study and molecular analysis to detect NAB2/STAT6 gene fusion, tumor protein-53 (TP53) and/or (telomerase reverse transcriptase) TERT promotor mutation were performed. The risk of metastasis was calculated using the Demicco risk stratification system (RSS). The results were combined and examined to assess the accuracy of risk stratification and classification. The most common location was in non-extremities; 66% were located in soft tissue or subcutaneous areas and 92.8% in deep locations. On microscopic analysis, 38.1% of tumors revealed hypercellularity with a predominant patternless and/or hemangiopericytic growth pattern; 13.4% had ≥4 mitoses/10HPF; 16.5% showed necrosis, and almost half the tumors showed at least focal myxoid areas. Dedifferentiation was observed in three tumors. Immunomarker expression in SFTs was as follows: CD34 92.9%, CD99 57.1%, Bcl2 67.9%, neuroendocrine markers (at least 1) 25.7%, Desmin 14.3%, CK(AE1/AE3) 3%, Apoptotic Protease Activating Factor (APAF-1) 87% and finally Ki-67 ≥ 10% in 14.4%. The NAB2/STAT6 gene fusion was detected in 50 tumors. After a median follow-up of 90 months, 9.3% recurred, 11.3% metastasized, 10.3% died of disease and 76.2% were free of disease. TERT mutations were detected in 40.6% of the SFTs; the TP53 mutation was detected in 17%, and only 9.3% showed both mutations. According to the Demicco RSS, 6.1%, 11.3% and 82.4% of the tumors were classified as high, intermediate or low-risk of metastasis, respectively. All high-risk tumors had ≥4 mitoses/10HPF, necrosis, Ki-67 ≥ 10, HTER and/or TP53 mutation and poor evolution. The intermediate risk SFTs with worse evolution displayed the HTER mutation. Almost all low-risk tumors had a favorable evolution, although four showed at least one adverse factor (Ki-67 ≥ 10, ≥4 mitoses/10HPF or high tumor size) and had a worse evolution. An integration of clinical, morphologic, immunohistochemical and molecular findings may improve risk stratification and classification and better predict patient outcome. The unfavorable course seems to be more frequent in high-risk SFTs, although it is not exceptional in low-risk SFTs either; hence, a long-term follow-up is required independently of the assigned risk stratification score. The inclusion of molecular findings in risk stratification systems could improve the precision in the classification of SFTs, especially those of intermediate risk. Future studies will be required to determine the most effective way to incorporate molecular analyses into RSS on SFTs. The coexistence of several adverse factors such as ≥4 mitoses/10HPF, necrosis, Ki-67 ≥ 10%, mutations in HTER and/or p53 may suggest a closer clinical follow-up regardless of the histological appearance of the tumor.

Mesenchymal tumours of the gastrointestinal tract

Mesenchymal tumours represent a heterogenous group of neoplasms encopassing benign, intermediate malignancy, and malignant entities. Sarcomas account for approximately 1% of human malignancies. In consideration of their rarity as well as of intrinsic complexity, diagnostic accuracy represents a major challenge. Traditionally, mesenchymal tumours are regarded as lesions the occurrence of which is mostly limited to somatic soft tissues. However, the occurrence of soft tissue tumours at visceral sites represent a well recognized event, and the GI-tract ranks among the most frequently involved visceral location. There exist entities such as gastrointestinal stromal tumours (GIST) and malignant gastointestinal neuroectodermal tumors that exhibit exquisite tropism for the GI-tract. This review will focus also on other relevant clinico-pathologic entities in which occurrence at visceral location is not at all negligible.

Lipomatous Solitary Fibrous Tumors Harbor Rare NAB2-STAT6 Fusion Variants and Show Up-Regulation of the Gene PPARG, Encoding for a Regulator of Adipocyte Differentiation

Solitary fibrous tumors (SFTs) harbor activating NAB2-STAT6 gene fusions. Different variants of the NAB2-STAT6 gene fusion have been associated with distinct clinicopathologic features. Lipomatous SFTs are a morphologic variant of SFTs, characterized by a fat-forming tumor component. Our aim was to evaluate NAB2-STAT6 fusion variants and to further study the molecular genetic features in a cohort of lipomatous SFTs. A hybrid-capture-based next-generation sequencing panel was employed to detect NAB2-STAT6 gene fusions at the RNA level. In addition, the RNA expression levels of 507 genes were evaluated using this panel, and were compared with a control cohort of nonlipomatous SFTs. Notably, 5 of 11 (45%) of lipomatous SFTs in the current series harbored the uncommon NAB2 exon 4-STAT6 exon 4 gene fusion variant, which is observed in only 0.9% to 1.4% of nonlipomatous SFTs. Furthermore, lipomatous SFTs displayed significant differences in gene expression compared with their nonlipomatous counterparts, including up-regulation of the gene peroxisome proliferator activated receptor-γ (PPARG). Peroxisome proliferator activated receptor-γ is a nuclear receptor regulating adipocyte differentiation, providing a possible explanation for the fat-forming component in lipomatous SFTs. In summary, the current study provides a possible molecular genetic basis for the distinct morphologic features of lipomatous SFTs.

The many faces of solitary fibrous tumor; diversity of histological features, differential diagnosis and role of molecular studies and surrogate markers in avoiding misdiagnosis and predicting the behavior

Background

Solitary Fibrous Tumor (SFT) is a distinct soft tissue neoplasm associated with NAB2-STAT6 gene fusion. It can involve a number of anatomic sites and exhibits a wide spectrum of histological features.

Main body

Apart from diversity in morphological features seen even in conventional SFT, two histologic variants (fat-forming and giant cell-rich) are also recognized. In addition, a malignant form and dedifferentiation are well recognized. Owing to diverse histological features and involvement of diverse anatomic locations, SFT can mimic other soft tissue neoplasms of different lineages including schwannoma, spindle cell lipoma, dermatofibrosarcoma protuberans, liposarcoma, gastrointestinal stromal tumor (GIST), malignant peripheral nerve sheath tumor (MPNST), and synovial sarcoma. SFT is classified as an intermediate (rarely metastasizing) tumor according to World Health Organization Classification of Tumors of Soft tissue and Bone, 5th edition. The management and prognosis of SFT differs from its malignant mimics and correct diagnosis is therefore important. Although SFT expresses a distinct immunohistochemical (IHC) profile, the classic histomorphological and IHC profile is not seen in all cases and diagnosis can be challenging. NAB2-STAT6 gene fusion has recently emerged as a sensitive and specific molecular marker and its IHC surrogate marker signal transducer and activator of transcription 6 (STAT6) has also shown significant sensitivity and specificity. However, few recent studies have reported STAT6 expression in other soft tissue neoplasms.

Conclusion

This review will focus on describing the diversity of histological features of SFT, differential diagnoses and discussing the features helpful in distinguishing SFT from its histological mimics.

Well-Differentiated/Dedifferentiated Liposarcoma Arising in the Upper Aerodigestive Tract: 8 Cases Mimicking Non-adipocytic Lesions

Well-differentiated (WDL) and dedifferentiated liposarcomas (DL) of the pharynx, larynx and oral cavity are rare, often mimicking benign lipomatous neoplasms or non-lipogenic mesenchymal tumors. Cases of WDL/DL arising in the upper aerodigestive tract, exclusive of the cervical esophagus, were reviewed. Morphologic features, ancillary studies, including fluorescence in situ hybridization (FISH) studies for CPM/MDM2, and clinical data was catalogued. Eight WDL/DL (4 WDL, 4 DL); were identified in patients ranging from 32 to 77 years (median 52.5 years; 6 males, 2 females) with sites of origin including hypopharynx (5 cases), larynx (2 cases) and oral cavity (1 case). Six of the 8 cases were received for expert consultation, and the remaining 2 cases were initially misdiagnosed as benign lymphangiomatous or fibroepithelial polyps. Morphologically, 4 tumors had areas mimicking various non-lipomatous soft tissue tumors including nodular fasciitis, mammary-type myofibroblastoma, low-grade myofibroblastic sarcoma and undifferentiated pleomorphic sarcoma, 2 cases simulated benign hypopharyngeal polyps, and 1 lesion was notable for a dense lymphoplasmacytic infiltrate suggestive of hematolymphoid neoplasm or IgG4-related sclerosing disease. FISH showed amplification of CPM/MDM2 (8/8 cases). All cases (4/4) with longer than 1-year of follow-up recurred (45-118 months) with 1 tumor showing progression to DL. WDL/DL presenting in the upper aerodigestive tract are rare and diagnostically challenging. Awareness of the morphologic spectrum of WDL/DL coupled with appropriate use of MDM2 FISH is essential for accurate classification and management, as these tumors appear to have a high risk for local recurrence and eventual dedifferentiation in these anatomical locations.

Benign lesions of the mediastinum: A review with emphasis on cytology and small biopsy specimens

This review focuses on the diagnosis of select benign processes, ranging from reactive entities to heterotopic tissues to neoplasms, which may occur in the mediastinum. Currently, the mediastinum can be evaluated and biopsied with endoscopic procedures. Therefore, cytopathology specimens, fine needle aspirations, and small biopsies play an important role in the diagnosis of these lesions. In this review, an emphasis is given to relevant clinical presentations, histologic and cytologic findings, differential diagnoses, ancillary testing, and interpretation. Pitfalls are reviewed and discussed in each section. It is important for both surgical pathologists and cytopathologists to be familiar with these entities and their cytologic and histologic features that may be helpful in reaching a diagnosis.

Solitary fibrous tumor involving the pancreas: report of the cytologic features and first report of a primary pancreatic solitary fibrous tumor diagnosed by fine-needle aspiration biopsy

INTRODUCTION

Solitary fibrous tumor (SFT) of the pancreas is rare, with only 16 reported cases in English studies. The cytologic features of pancreatic SFT have not been well described. We report 2 cases of SFT (1 primary and 1 metastatic) involving the pancreas and discuss the cytomorphologic findings, including the first primary SFT of the pancreas specifically diagnosed using cytology.

MATERIALS AND METHODS

The cases of 2 patients with a diagnosis of SFT of the pancreas from material obtained via fine needle aspiration (FNA) are reported. Clinical information was retrieved from the patients' medical records. The FNA cytology slides, previous relevant surgical pathologic findings, and findings from subsequent pancreatic resections were reviewed.

RESULTS

Of the 2 patients, 1 had had secondary involvement of the pancreas from a primary central nervous system SFT, and 1 had had a primary pancreatic SFT diagnosed by FNA. Immunohistochemistry for STAT6 was crucial for establishing the diagnosis using FNA.

CONCLUSIONS

We have reported 2 cases of SFT involving the pancreas, including the first reported case of primary pancreatic SFT diagnosed preoperatively using FNA. Metastatic SFT from central nervous system primaries should be considered when diagnosing SFT of the pancreas.

Controversial issues in soft tissue solitary fibrous tumors: A pathological and molecular review

The clinical evolution of solitary fibrous tumor (SFT) remains unclear. Although various clinical, morphological and molecular criteria may indicate increased risk of malignancy, some SFT can still progress despite having a clearly benign appearance. Various risk stratification systems have been proposed, but unfortunately they are not sufficient to precisely determine the malignant potential. In this review, we discuss current knowledge on SFT, focusing on the following controversial issues: (i) the diverse morphologic spectrum: 'the great simulator;' (ii) malignant transformation or dedifferentiation; (iii) current risk stratification systems; and (iv) molecular factors associated with clinical evolution. The morphological spectrum of SFT and the list of differential diagnoses continue to expand. Both have increased considerably since the first descriptions of specific molecular alterations. A classification of malignant SFT should not be based on histology alone. The correlation of all pathological and molecular factors is recommended; its inclusion in risk stratification systems may help to improve diagnosis and prognosis.

Solitary fibrous tumor: a case series identifying pathological adverse factors-implications for risk stratification and classification

Solitary fibrous tumors (SFTs) are a rare type of mesenchymal lesion in which specific clinicopathologic factors have been related to patient outcome. We collected clinical, pathological, and molecular data of 28 patients with histologically confirmed SFT having at least one pathological factor associated with aggressive behavior. Molecular analysis to detect NAB2/STAT6 gene fusion, TP53, and/or TERT promoter mutation was performed. We analyzed the pathological factors predictive of recurrence/metastasis and compared with clinical outcome. The risk of metastasis was calculated using four previously described scoring systems. Histopathologically, all tumors revealed hypercellularity, 11 had ≥ 4 mitoses/10 HPF, and 12 showed necrosis. Dedifferentiation was observed in three tumors. STAT6 was positive in all cases. Desmin, p16, INSM1, and HTER immunoexpressions were detected in 14, 18, 21, and 46% of the SFT, respectively. The NAB2/STAT6 gene fusion was detected in 16 tumors. After a median follow-up of 34 months, 32.0% recurred, 32.1% metastasized, and 35.7% died of disease. TERT mutations were detected in almost half the tumors. Tumors with TP53 mutations or with TP53 and TERT promoter mutations were almost always classified as high risk, and the patients developed metastases and/or died of disease. Tumors with intermediate-risk and TERT mutation had a worse evolution. SFTs with adverse pathological parameters were not always related with a poor outcome, thus confirming the unpredictable clinical behavior of SFT. The inclusion of molecular factors (TP53 and TERT promoter status) may provide new prognostic indicators for future risk stratification systems, especially in the intermediate-risk group.

Foot soft tissue myopericytoma: Case-report and review

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Myopericytoma is a rare tumor of deep soft tissues.

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Small tumefying at the level of the plantar region, between the 2nd and 3rd toe of the right foot.

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Neoformation of 0.6 cm in diameter, well circumscribed, capsulated and with free resection margins.

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The immunohistochemical profile was consistent for positive alpha-actin and negative desmine.

Introduction

Myopericytoma is a rare tumor of deep soft tissues, originating from pericytes and characterized by numerous thin walled blood vessels.

Case report

We report a case of myopericytoma found at the level of the second toe of the right foot.

A patient came to the Endocrinology Surgery Department of Catania Polyclinic because of a presence of a small swelling in the plantar region, between the 2nd and 3rd toe of the right foot. At the anatomopathological examination, the escalated lesion showed a neoformation of 0.6 cm in diameter, well circumscribed, capsulated, with myopericytoma diagnosis.

Discussion

Its histopathological appearance is similar to myofibromatic lesions from glomic and angiomyoma tumors. It is a rare tumor that affects all ages with a peak after 50 years 3. The most frequent localization is at the lower extremities, particularly in soft subcutaneous tissues, but can rarely occur in other sites.

Conclusion

At the anatomopathological evaluation, the immunohistochemical examination for the correct formulation of the diagnosis is essential and an adequate surgical excision is important.

Diagnostically Challenging "Fatty" Retroperitoneal Tumors

A variety of benign and malignant retroperitoneal mesenchymal lesions may have a component of adipose tissue, including entities such as lipoma, myolipoma, angiomyolipoma, solitary fibrous tumor, genital stromal tumors, and well-differentiated/dedifferentiated liposarcoma. Although definitive diagnosis is usually straightforward on the complete resection specimen, it is often more difficult to workup these lesions on small biopsy samples. This review focuses on challenging diagnostic scenarios of retroperitoneal lesions with a "fatty" component and provides major differential diagnoses for commonly encountered morphologic patterns, clinicopathologic features of the various entities, and strategy for use of ancillary techniques, such as immunohistochemistry and cytogenetic studies.

Update on Select Benign Mesenchymal and Meningothelial Sinonasal Tract Lesions

Several benign and malignant mesenchymal and meningothelial lesions may preferentially affect or extend into the sinonasal tract. Glomangiopericytoma (GPC, formerly sinonasal-type hemangiopericytoma) is a specific tumor with a predilection to the sinonasal tract. Sinonasal tract polyps with stromal atypia (antrochoanal polyp) demonstrate unique histologic findings in the sinonasal tract. Juvenile nasopharyngeal angiofibroma (JNA) arises from specialized tissue in this location. Meningioma may develop as direct extension from its intracranial counterpart or as an ectopic tumor. Selected benign mesenchymal tumors may arise in the sinonasal tract and pose a unique differential diagnostic consideration, such as solitary fibrous tumor and GPC or lobular capillary hemangioma and JNA. Although benign and malignant vascular, fibrous, fatty, skeletal muscle, and nerve sheath tumors may occur in this location, this paper focuses on a highly select group of rare benign sinonasal tract tumors with their clinicopathological and molecular findings, and differential diagnosis.

Pleural fat-forming variant of solitary fibrous tumor

The fat-forming variant of solitary fibrous tumor is rare. It occurs predominantly in the deep soft tissues of the retroperitoneum and thigh. We describe a case of fat-forming solitary fibrous tumor arising from the pleura, which was successfully treated using a video-assisted thoracoscopic approach. The patient remained free of recurrence 2 years after surgery and continues to be under long-term follow-up.

STAT6 rabbit monoclonal antibody is a robust diagnostic tool for the distinction of solitary fibrous tumour from its mimics

Recurrent NAB2-STAT6 gene fusions have recently been identified in solitary fibrous tumour by next generation sequencing. Our aim was to examine the sensitivity and specificity of STAT6 immunohistochemistry for solitary fibrous tumour versus other morphologically similar soft tissue tumours. STAT6 expression was evaluated in 54 solitary fibrous tumours of various sites and 99 soft tissue tumours in the histological differential diagnosis. We used a rabbit monoclonal STAT6 antibody (1:100), which has not been reported by others, on formalin fixed, paraffin embedded whole sections and tissue microarray slides. Only nuclear staining of STAT6 was considered positive. Distribution of staining was scored as: 0 (no staining), 1+ (1-25%), 2+ (26-50%), 3+ (>50%). Intensity was scored as weak, moderate or strong. Nuclear STAT6 staining was present in all SFT cases tested (54/54, sensitivity 100%), regardless of histology, anatomical site or CD34 status. The majority of cases showed 3+ and strong staining. All tested cases of cellular angiofibroma (0/9), myofibroblastoma (0/10), spindle cell lipoma (0/10), benign fibrous histiocytoma (0/13), dermatofibrosarcoma protruberans (0/9), low-grade fibromyxoid sarcoma (0/7), schwannoma (0/8), desmoid-type fibromatosis (0/8), monophasic synovial sarcoma (0/11), malignant peripheral nerve sheath tumour (0/7), and mesenchymal chondrosarcoma (0/7) were negative for STAT6 (specificity 100%). Our study further supports the utility of STAT6 immunohistochemistry as an adjunct in the diagnosis of solitary fibrous tumour.

Infantile haemangiopericytoma: a rare congenital cervical tumour

Objective:

Infantile haemangiopericytoma is a rare childhood vascular tumour of borderline malignancy and unpredictable clinical course. It can present a diagnostic challenge due to indeterminate clinical, radiological and pathological features. This report presents the case of a large congenital haemangiopericytoma of the neck in a neonate, and discusses diagnosis, imaging, pathology and surgical management.

Clinical presentation:

A full-term neonate presented with a large posterior neck mass at birth. Pre-operative radiological appearances were suggestive of teratoma, but following surgical excision the diagnosis of infantile haemangiopericytoma was confirmed on histological analysis. There were no signs of recurrence at 12-month follow up.

Conclusion:

Haemangiopericytoma can follow an aggressive course in adults, including local recurrence and metastasis. The infantile variant is rare but typically follows a distinct clinical course, and is associated with more benign behaviour compared with similar tumours in adults and children over one year. Congenital haemangiopericytoma can be effectively treated with surgery, without requiring adjuvant therapy.

Tail-end troubles: imaging of soft-tissue buttock tumours

Primary soft-tissue buttock tumours are relatively common entities, although they are infrequently reported in the literature. The buttock can be a difficult anatomical site to treat soft-tissue tumours due to the proximity of the sciatic nerve and the propensity of tumours at this site to extend into the pelvis and perineum. Therefore, the radiologist plays an important role in the multidisciplinary assessment of these lesions. Cross-sectional imaging, principally magnetic resonance imaging, is used to determine the exact location and extension of the tumour. Furthermore, certain tumours have characteristic imaging appearances that can help to establish a suitably ordered differential diagnosis. From our prospectively maintained database at The Royal Marsden Hospital, including 225 cases that were treated at the Sarcoma Unit over a 30 year period, we present examples of benign and malignant primary soft-tissue buttock tumours and describe the pertinent imaging characteristics, with emphasis on computed tomography and magnetic resonance imaging findings.

Fat-forming variant of solitary fibrous tumour of the pleura: CT findings

The fat-forming variant of solitary fibrous tumour (SFT) was previously called lipomatous haemangiopericytoma and is a rare variant of solitary fibrous tumour. It predominantly occurs in the deep soft tissues of the retroperitoneum and thigh. Only a handful of cases involving the perineum, spine, thoracic wall and pelvic cavity have been reported in the radiological literature and the fat-forming variant of SFT involving the pleura has not been previously reported. Herein, we report the CT findings of a case of the fat-forming variant of SFT involving the pleura that was treated by excision. Chest CT showed a large lobulated heterogeneous fatty mass with a multifocal enhancing soft-tissue component in the left lower hemithorax. Although rare, the fat-forming variant of SFT of the pleura should be added to the differential diagnosis of fat-containing pleural soft-tissue tumours.

Lipomatous hemangiopericytoma of the stomach: A case report and a review of literature

Lipomatous hemangiopericytomas (LHPCs) are rare soft-tissue tumors that are histologically characterized by hemangiopericytomatous vasculature and the presence of mature adipocytes. We present the clinicopathological features of a case of gastric LHPC in a 56-year-old female, along with a literature review. Endoscopy and endoscopic ultrasound showed a submucosal tumor 0.8 cm across in the greatest dimension in the lesser curvature side of the gastric antrum. Grossly, the well-defined mass had a solid and tan-white cut surface admixed with myxoid regions and yellowish areas. Histological examination revealed a submucosal well-circumscribed lesion composed of cellular nodules with the classic appearance of an hemangiopericytoma admixed with clusters and lobules of mature adipocytes. The ill-defined tumor cells had weakly eosinophilic cytoplasm and contained spindled nuclei with occasional small nucleoli. Nuclei atypia and mitoses were absent, and no cellular atypia, necrosis or vascular invasion was observed. Immunohistochemistry showed that the tumor cells were diffusely positive for CD34, CD99, and vimentin and were focally reactive for bcl-2. This is the first known report of an LHPC in the stomach. The patient was followed for 12 mo without any evidence of metastasis or recurrence.

Primary retroperitoneal spindle cell liposarcoma: pathological and immunohistochemical findings

Spindle cell liposarcoma (SCLS) is presently regarded as a rare variant of well-differentiated liposarcoma (WDLPS), which has the potential for aggressive clinical behavior. WDLPS occurs most frequently in the limbs and retroperitoneum. The most common site of SCLS occurrence is the upper limbs or shoulder girdle. Herein we report the first case of primary retroperitoneal SCLS. A 60-year-old Japanese man presented with a right inferior abdominal mass. Complete excision of the mass displayed a yellowish spherical tumor with a well-circumscribed appearance measuring 98 x 95 mm. Pathological examination of the tumor revealed a neural-like spindle cell proliferation set in a fibrous background that was associated with an atypical lipomatous component, which usually included lipoblasts. Mitotic cells were scarce. Immunohistochemical analysis demonstrated that lipoblasts were S100 positive, spindle cells were CD34 positive, and both spindle cells and lipoblasts were MDM2 negative. The Ki-67 labeling index was <2%. At one year follow up, the patient was alive without local recurrence or metastasis. Although the proliferative activity of this tumor did not indicate strong malignancy, retroperitoneal liposarcoma generally has a poor prognosis. Accumulation of cases of SCLS is necessary to facilitate a more accurate evaluation of the pathology and clinical behavior of this tumor.

Solitary fibrous tumors of the soft tissues: review of the imaging and clinical features with histopathologic correlation

OBJECTIVE

Solitary fibrous tumors are rare soft-tissue tumors of submesothelial origin with variable malignant potential. Most of these tumors originate within the thoracic cavity, but they can occur in a variety of sites, including the abdomen, pelvis, and soft tissues and muscles. The purpose of this study was to review the imaging findings with clinicopathologic correlation in 34 cases.

CONCLUSION

The finding of a large, solid, vascular tumor, particularly with prominent feeding vessels or a visible fatty component, should alert the radiologist to the possible diagnosis of solitary fibrous tumor. Percutaneous biopsy carries minimal risk and should be used for definitive diagnosis of these lesions, which in many cases are curable with surgery. The prognosis is good for patients with benign tumors but variable for those with malignant tumors.

Management of a retrorectal lipomatous hemangiopericytoma by preoperative vascular embolization and a multidisciplinary surgical team: report of a case

Large, highly vascular pelvic tumors can be challenging to manage, and bleeding is a major concern of the surgeon. Other concerns relate to the risk of injury to associated pelvic structures, difficulties in operative exposure, and complete tumor removal. We report an unusual case of a massive retrorectal lipomatous hemangiopericytoma managed successfully by preoperative vascular embolization and a multidisciplinary surgical team. The combined efforts of an interventional radiologist, vascular surgeon, orthophedic oncologist, and colorectal surgeon led to successful and safe complete removal of the tumor.

Lipomatous hemangiopericytoma of the skull base and parapharyngeal space

OBJECTIVE

To discuss the diagnosis and clinical management of lipomatous hemangiopericytoma.

STUDY DESIGN

Case report.

SETTING

Tertiary referral center.

PATIENT

A 36-year-old woman was encountered with symptoms of facial numbness, blurred vision, headache, and lightheadedness of 6 weeks' duration. Magnetic resonance imaging revealed a 5.0-cm mass in the right parapharyngeal space and skull base extending inferiorly to the level of the carotid bifurcation. The mass was consistent radiographically with a glomus jugulare tumor, and surgical extirpation was performed.

INTERVENTION

The patient underwent a transtemporal approach to the right posterior fossa and jugular foramen including mastoidectomy and isolation and preservation of Cranial Nerves VII, X, XI, and XII. Microscopic analysis of the mass revealed a highly cellular spindled mesenchymal tumor with a pericytoma pattern. Almost half of the mass displayed a mature lipomatous component. These findings were consistent with a lipomatous hemangiopericytoma.

RESULTS

The authors describe the first case of lipomatous hemangiopericytoma involving the skull base. This rare variant of the more common hemangiopericytoma has been described previously in the retroperitoneal and lower extremities. Although one case of lipomatous hemangiopericytoma has been described in the occipital region, this is the first report of this entity involving the parapharyngeal space, skull base, and jugular foramen.

CONCLUSION

The authors demonstrate that lipomatous hemangiopericytoma can occur in the parapharyngeal space and skull base. Once thought to be an aggressive variant, this tumor has an extremely low propensity for distant or local recurrence. Adjuvant therapies such as radiation and chemotherapeutic agents are reserved for recurrent or metastatic lesions.

Pulmonary lipomatous hemangiopericytoma: report of a rare tumor and comparison with solitary fibrous tumor

Lipomatous hemangiopericytoma is a rare mesenchymal tumor showing areas of lipid-containing cells admixed with a spindle-cell component. Like other hemangiopericytomas, it shows a similar vascular pattern to solitary fibrous tumor and, partly for this reason, it and other hemangiopericytomas have been subsumed into solitary fibrous tumor. The present study provides a comprehensive documentation of a single case of pulmonary lipomatous hemangiopericytoma of the lung, the first to be described at this site, and compares it with solitary fibrous tumor, in terms of clinical, histological, immunohistochemical, ultrastructural, and cytogenetic findings. Apart from the lipid-laden-cell component, pulmonary lipomatous hemangiopericytoma and solitary fibrous tumor were similar histologically. Bcl-2 was positive in both. CD34 was minimally expressed in pulmonary lipomatous hemangiopericytoma, which possessed some non-descriptive intercellular junctions, a feature shared by solitary fibrous tumor, which was CD34 positive. However, one of the latter was rich in gap junctions, a feature consistent with strong connexin (Cx) 43 staining and the existence, hitherto unappreciated, of a CD34/Cx43-positive tumor cell network. In pulmonary lipomatous hemangiopericytoma, chromosomal deletions of 43-44, X, -Y were found. In solitary fibrous tumor, 46, XY, del(13)(q?) abnormalities and abnormalities involving chromosome 10 were frequently observed. These similarities and differences are discussed in the context of the currently favored diagnostic fusion of hemangiopericytoma and solitary fibrous tumor.

Solitary fibrous tumor with pseudo-lipoblasts involving the sublingual gland: report of a case and review of the literature

Solitary fibrous tumors (SFTs) are mesenchymal neoplasms uncommonly occurring in the salivary glands. In rare instances, SFTs can contain mature fat, atrophic fat, or vacuolated cells previously termed 'pseudo-lipoblasts', which may be misinterpreted as a feature of malignancy. We report an unusual tumor with pseudo-lipoblasts occurring in the sublingual gland. The tumor exhibited a prominent hemangiopericytic pattern, bland cytology, and immunohistochemical and morphologic features consistent with that of an SFT. A review of 15 cases of SFTs of the salivary glands is presented. Emphasis is laid upon the histologic differential diagnosis and the clinical features of these tumors.

Solitary fibrous tumour and haemangiopericytoma: evolution of a concept

Haemangiopericytoma (HPC) was described in 1942 by Stout and Murray as a distinctive soft tissue neoplasm, presumably of pericytic origin, exhibiting a characteristic well-developed "staghorn" branching vascular pattern. Over the years, it appeared that this growth pattern was a non-specific one, shared by numerous, unrelated benign and malignant lesions, and that HPC was better considered as a diagnosis of exclusion. Three categories of lesion may now be individualized within the heterogeneous group of HPC-like neoplasms. The first category corresponds to those non-HPC neoplasms that occasionally display HPC-like features (e.g. synovial sarcoma). Lesions belonging to the second category show clear evidence of myoid/pericytic differentiation and correspond to true HPCs. They generally show a benign clinical course, and include glomangiopericytoma/myopericytoma, infantile myofibromatosis (previously called infantile HPC), and a subset of sinonasal HPCs. The third category is the solitary fibrous tumour (SFT) lesional group, which includes fibrous-to-cellular SFTs, and related lesions such as giant cell angiofibromas and lipomatous HPCs. In practice, any HPC-like lesion can be allocated to one of these categories, leaving the ill-defined "haemangiopericytoma" category empty.

Fat-containing variant of solitary fibrous tumor (lipomatous hemangiopericytoma) arising on surface of kidney

Fat-containing variant of a solitary fibrous tumor is a recently recognized benign soft-tissue tumor that usually affects the thigh and retroperitoneum. We report a 51-year-old woman with a fat-containing variant of a solitary fibrous tumor that is the first reported case involving a visceral organ. The tumor was well delineated and seemed to arise from the renal capsule, radiographically and macroscopically. The tumor microscopically mimicked a solitary fibrous tumor but exhibited focal aggregates of fat cells. A fat-containing variant of a solitary fibrous tumor involving the kidney should be distinguished from spindle cell carcinoma, angiomyolipoma, gastrointestinal stromal tumor, and cellular schwannoma.

Low-grade sarcomas with CD34-positive fibroblasts and low-grade myofibroblastic sarcomas

A subset of low-grade fibrosarcomas is composed of CD34-positive spindle cells. These include dermatofibrosarcoma, its morphologic variants, and its associated fibrosarcoma, solitary fibrous tumor, hemangiopericytoma and their malignant counterparts, and some cases of myxoinflammatory fibroblastic sarcoma. Dermatofibrosarcoma and related lesions are characterized by a t(17;22)(q22;q13) rearrangement resulting in fusion of the genes COL1A (17q21-22) and PDGFB1 (22q13). Solitary fibrous tumor displays varying cellularity and fibrosis and a peripheral hemangiopericytomatous pattern; most tumors formerly called hemangiopericytoma are now subsumed into the category of solitary fibrous tumor, although a few strictly defined examples are recognized; however, these are probably not composed of pericytes. Myofibroblastic malignancies are best identified by electron microscopy, with which varying degrees of differentiation, including the presence of fibronexus junctions, can be identified. Low-grade sarcomas showing myofibroblastic differentiation include myofibrosarcomas and inflammatory myofibroblastic tumors. Myofibrosarcomas are spindle cell neoplasms that occur in children or adults in the head and neck, trunk, and extremities as infiltrative neoplasms and that display a fascicular or fasciitis-like pattern with focal nuclear atypia and variable expression of myoid antigens. These sarcomas are prone to recurrence and a small number metastasize. Inflammatory myofibroblastic tumor (synonymous with inflammatory fibrosarcoma) is a neoplasm arising predominantly in childhood, and frequently in intraabdominal locations. It has spindle cells in fascicular, fasciitis-like and sclerosing patterns, with heavy chronic inflammation including abundant plasma cells. Many IMT have clonal chromosomal abnormalities involving 2p22-24, and fusion of the ALK gene with tropomyosin 3 (TPM3-ALK) or tropomyosin 4 (TPM4-ALK) is found in a subset.

Lipomatous hemangiopericytoma of the head and neck: immunohistochemical and DNA ploidy analyses

BACKGROUND

Lipomatous hemangiopericytoma (LHPC) is a newly described rare soft tissue tumor with unpredictable biologic behavior and is difficult to diagnose by conventional histologic parameters. The molecular analyses of this entity to date are sparse. Only a few cases of LHPC have been reported. Although one case of LHPC in the sinonasal region was briefly reported, this is the first case in the head and neck region with detailed clinicopathologic features and molecular analysis of this entity.

METHODS

We reported a case of LHPC in a 55-year-old woman with a slowly growing lesion in the occipital area that was diagnosed by CT and MRI and removed surgically. Immunohistochemical and DNA ploidy analyses were performed.

RESULTS

A panel of 16 markers was included for immunohistochemical analysis. Diffuse immunopositivity of CD57 in our case provides supportive evidence that LHPC is linked with HPC because this marker is also present in approximately 50% of conventional HPCs. CD57 should be used in the immunohistochemical panel in any lesion suspected to be LHPC. Furthermore, CD57 along with CD34 and XIIIa is thought to stain for primitive mesenchymal stem cells, suggesting a bimodal/multimodal differentiation of LHPC. By flow cytometry, we found that tumor cells were 100% diploid with the S-phase fraction (SPF) being 3.21%. A significant positive correlation was detected between nuclear proliferating index and SPF (p < 0.001, by Spearman analysis). These findings provide molecular evidence indicating a benign nature of LHPC.

CONCLUSIONS

Contrary to the old belief that HPC has an aggressive nature, this variant of tumor looks less aggressive. The patient was followed for 1 year without any evidence of recurrence, supporting our pathologic hypothesis.

Fine-needle aspiration smears from lipomatous hemangiopericytoma need not be confused with myxoid liposarcoma

Lipomatous hemangiopericytoma (LHPC) is a rare benign soft tissue tumor that may mimic soft tissue sarcoma clinically. Despite the fact that LHPC shares most of the histologic features with solitary fibrous tumor, it may be occasionally misdiagnosed as myxoid liposarcoma or some other type of spindle-cell sarcoma. While some studies have addressed the histological features and origin of LHPC, no reports of cytological findings have been published. The author describes the cytological features of LHPC in two patients with correlations to histological and clinical findings. One of aspirates was misdiagnosed as being myxoid liposarcoma, while the other one was correctly diagnosed by a combination of FNAB and core needle biopsy (CNB). Cytological evaluation of LHPC can be problematic due to its rarity and to its similarity with other spindle-cell or fatty tumors. Correct diagnosis requires an awareness of cytologic features of this rare tumor and the use of ancillary studies.

Sinonasal-type hemangiopericytoma: a clinicopathologic and immunophenotypic analysis of 104 cases showing perivascular myoid differentiation

Sinonasal-type hemangiopericytoma is an uncommon upper aerodigestive tract tumor of uncertain cellular differentiation. We report 104 cases of sinonasal-type hemangiopericytoma diagnosed between 1970 and 1995 from the files of the Armed Forces Institute of Pathology. There were 57 females and 47 males ranging in age from 5 to 86 years (mean 62.6 years). The most common clinical presentation was airway obstruction (n = 57) and/or epistaxis (n = 54), with symptoms averaging 10 months in duration. The tumors involved the nasal cavity alone (n = 47) or also a paranasal sinus (n = 26), were polypoid, and measured an average of 3.1 cm. Histologically, the tumors were submucosal and unencapsulated and showed a diffuse growth with fascicular (n = 37) to solid (n = 50) to focally whorled (n = 7) patterns. The tumor cells were uniform in appearance with minimal pleomorphism and had spindle-shaped (n = 82) to round/oval (n = 18) nuclei with vesicular to hyperchromatic chromatin and eosinophilic to amphophilic to clear-appearing cytoplasm with indistinct cell borders. Multinucleated (tumor) giant cells were identified in a minority of cases (n = 5). Mitotic figures were inconspicuous and necrosis was absent. The tumors were richly vascularized, including staghorn-appearing vessels that characteristically had prominent perivascular hyalinization (n = 92). An associated inflammatory cell infiltrate that included mast cells and eosinophils was noted in the majority of cases (n = 87). The immunohistochemical profile included reactivity with vimentin (98%), smooth muscle actin (92%), muscle specific actin (77%), factor XIIIa (78%), and laminin (52%). Surgery was the treatment of choice for all of the patients; adjunctive radiotherapy was given to four patients. Recurrences developed in 18 patients within 1-12 years from diagnosis. Ninety-seven patients were either alive (n = 51, mean 16.5 years) or dead (n = 46, mean 9.6 years) but free of disease. Four patients had disease at the last follow-up: three died with disease (mean 3.6 years) and one patient is alive with disease (28.3 years). Recurrent tumor (17.8%) can be managed by additional surgery. The majority of sinonasal-type hemangiopericytomas behave in a benign manner with excellent long-term prognosis (88% raw 5-year survival) following surgery alone. Sinonasal-type hemangiopericytomas have a characteristic light microscopic appearance with an immunophenotypic profile resembling that of glomus tumors.