Fibroblastic polyp of the colon and colonic perineurioma: 2 names for a single entity?

Polypoid Kaposi Sarcoma Involving the Lower Gastrointestinal Tract: Clinicopathologic Study of 15 Cases

CONTEXT.—

Gastrointestinal manifestations of Kaposi sarcoma are rare but may cause morbidity. Lower gastrointestinal involvement is particularly rare, and lesions may resemble conventional bowel polyps.

OBJECTIVE.—

To study 15 patients who presented with lower gastrointestinal tract Kaposi sarcoma with polypoid architecture.

DESIGN.—

The surgical pathology files of the departments of pathology at multiple institutions were searched for cases of Kaposi sarcoma forming polyps in the lower gastrointestinal tract (jejunum, colon, rectum); 15 cases with such features were identified. Clinicopathologic information was extracted from the medical record and documented by reviewing individual hematoxylin-eosin-stained slides.

RESULTS.—

The patients were 13 men and 2 women aged 26-80 years (median = 44 years). Gastrointestinal tract involvement was multifocal in 11 cases and unifocal in 4. The tumors involved the rectum, rectosigmoid junction, cecum, ascending colon, transverse colon, and descending colon and presented as polypoid lesions measuring 0.2-2.1 cm. Six patients had upper gastrointestinal tract involvement in addition to lower gastrointestinal lesions. Histologically, the tumors were characterized in 6 cases by a dense spindle cell proliferation in the lamina propria; however, the remaining cases showed only a subtle fascicular spindle cell proliferation in the lamina propria that did not form an expansile mass.

CONCLUSIONS.—

Biopsies of gastrointestinal polyps showing absence of the common features of hyperplastic or adenomatous polyps, particularly in immunocompromised patients, should be carefully examined for the presence of a stromal spindle cell proliferation. Use of immunohistochemical stains, particularly human herpesvirus-8, can help in establishing the correct diagnosis.

Gastrointestinal Tract Perineuriomas and Benign Fibroblastic Polyps: Case Report and Comprehensive Systematic Review

Background: Perineurioma is a rare benign peripheral nerve sheath tumor that can arise in various body locations. In the gastrointestinal (GI) tract, perineuriomas are uncommon and have only been reported in case reports and case series. In addition, a new classification suggests reclassifying benign fibroblastic polyps as perineurioma when they show positive markers of perineurial differentiation. Objective: This study aims to enhance understanding of GI tract perineuriomas by presenting a new case and conducting a systematic literature review. Methods: We described a new case of colonic perineurioma and systematically reviewed all case reports and case series on GI perineuriomas and benign fibroblastic polyps with perineurial markers. We searched ScienceDirect, PubMed/MEDLINE, and Web of Science up to May 2024. Results: A total of 148 cases were analyzed, and most of the cases were published in the last decade (2014-2024). The majority were females (59.46%), with a mean age of 51 years (standard deviation [SD] ±14.87). Most GI perineuriomas (87.5%) were in the distal colon, predominantly in the sigmoid/rectosigmoid (56%) and rectum (14%). Outside the colon, the stomach was the most affected site (7 of 10 cases), with fewer cases in the small intestine and esophagus. The two most commonly performed stains were for epithelial membrane antigen (EMA) and glucose transporter 1 (GLUT-1), at 75% and 56% of cases, respectively. Noncolonic perineuriomas were generally larger and more symptomatic than colonic ones. Submucosal polyps were more likely symptomatic than mucosal polyps. Conclusion: Perineurioma in the GI tract is a rare benign polyp mainly identified in the distal colon. Its rarity and limited follow-up data restrict our understanding of recurrence rates. We recommend reporting uncommon polyp locations, detailing polyp morphologies, and using at least two markers for classification.

Epithelial-Stromal Polyp With Features of Perineurioma Lacking Covering Serrated Crypts Associated With a Sessile Serrated Lesion With High-Grade Dysplasia of the Colon: A Case Report

A 79-year-old woman received a colonoscopy, and 6 polyps were found in the proximal colon. Histologically, four polyps were conventional tubular adenomas. Interestingly, one protuberant polyp was a sessile serrated lesion (SSL) with high-grade dysplasia being regarded as a potent precursor lesion for colorectal cancers. The polyp was connected with a flat-type SSL. Furthermore, another polyp was a bland spindle cell lesion filling the lamina propria. The polyp lacked covering serrated epithelium. Although the mesenchymal neoplasm displayed architectural features of perineurioma, immunoexpression of epithelial membrane antigen (EMA) and GLUT1 was negative. Accordingly, the benign mesenchymal neoplasm was considered an unusual epithelial-stromal polyp with a perineurioma-like lesion. In cases of usual perineuriomas, stromal cell proliferation is suggested to be a concern for serrated crypts that often harbor BRAF mutation. However, the mechanical nature of the proliferation of stromal cells in the polyps without serrated crypts is unknown. For the present case, proliferation of the mesenchymal cells of the epithelial-stromal polyp was suspected to relate to the serrated lesion near the polyp. Moreover, it is also presumed that the occurrence of the six polyps, including the serrated lesion, mesenchymal neoplasm, and tubular adenomas in the proximal colon, took part in both the BRAF and WNT signal pathways.

Gastric Perineurioma: A Case Report and Review of the Literature

Perineuriomas of the gastrointestinal tract, formerly known as benign fibroblastic polyps, most commonly occur as polyps on screening colonoscopy, particularly in the distal colon. Gastric examples are exceedingly rare. We report the sixth patient with a gastric perineurioma in a 57-year-old female. Histologically, the lesion was composed of bland spindle cells without cytologic atypia or mitotic activity located in the gastric lamina propria. The spindled cells were strongly positive for GLUT1 and focally reactive for epithelial membrane antigen (EMA). The morphologic and immunophenotypic findings were those of gastric perineurioma.

Calcifying pseudoneoplasm of neuroaxis (CAPNON): a comprehensive immunohistochemical and morphological characterization of five cases

Calcifying pseudoneoplasm of neuroaxis (CAPNON) is a rare lesion of the central nervous system with uncertain histogenesis. We further explored phenotypic spectrum of the entity with respect to possible histogenesis. We collected 5 cases of CAPNONs, performed a detailed morphological assessment, and performed an extensive immunohistochemical analysis (EMA, progesterone receptors, MUC4, SSTR2A, cytokeratin AE1/3, cytokeratin 18, GFAP, neurofilaments, desmin, nestin, synaptophysin, S100 protein, SOX10, CD56, Podoplanin, SATB2, ERG, CD45, and CD163) to elucidate the histogenesis. Furthermore, we performed NGS analysis of one case. The clinical course was benign in all cases. All lesions showed extensively calcified matrix in multilobular arrangement, with a palisade of osteoblast-like cells. Characteristic fibrohyaline matrix was notable in 4/5 cases, while one case was myxoid with rod-like calcifications. Metaplastic lamellar bone was present in 4/5 cases and psammoma bodies were present in 2/5 cases. In 4/5 cases, areas of entrapped glial tissue were present. Expression of EMA was focally present in 3/5 cases, SSTR2A and nestin in 2/5 cases, and progesterone receptor in 2/5 cases in rare cells. We did not observe concomitant expression of EMA, SSTR2A, and progesterone receptor in the same cellular subsets. In one case, NGS showed multiple chromosomal alterations and missense mutation in PIK3CA, attributable to the admixed meningothelial population compatible with meningioma. In another case, biphasic proliferation with myoepithelial phenotype was present. The lesions showed no lineage-specific immunoprofile. Additional pathology was identified in two cases, furthermore suggestive of a possible reactive origin of the lesion.

Cap-assisted Endoscopic Mucosal Resection of Rectal Perineurioma Mimicking a Neuroendocrine Tumor

Colorectal perineuriomas are benign mucosal-based mesenchymal tumors composed of perineurial cells and show serrated or hyperplastic crypts in epithelium on histopathological evaluation. Most perineuriomas are usually presented as sessile polyps and often as subepithelial tumors. In this case, colonoscopy revealed a rectal subepithelial tumor (measuring approximately 7 mm) with yellowish- colored normal mucosa. A rectal neuroendocrine tumor was suspected, and cap-assisted endoscopic mucosal resection was performed. Histopathological examination of the resected specimen revealed bland spindle cells showing immunopositivity for CD34. The patient was finally diagnosed with rectal perineurioma.

Spindle cell proliferations of the sigmoid colon, rectum and anus: a review with emphasis on perineurioma

A wide range of spindle cell proliferations are found uncommonly in the sigmoid colon, rectum and anus. They usually present as polyps, and include reactive lesions and benign and malignant neoplasms which may be primary or metastatic. They are less frequently described in the literature compared to those in the upper gastrointestinal tract, and may be underdiagnosed. The widespread use of sigmoidoscopy in symptomatic patients and bowel cancer screening programmes means that histopathologists must be aware of, and adopt a logical approach to, diagnosing spindle cell proliferations in biopsy and polypectomy specimens. This is particularly relevant given the strong association of some mesenchymal polyps with hereditary cancer syndromes. This review article will focus on perineurioma and the recent debate in relation to its overlap with fibroblastic polyp. The clinical, endoscopic, histological and immunohistochemical features of spindle cell proliferations which should be considered in the differential diagnosis of perineurioma will be discussed. There is also a brief reference to malignant spindle cell tumours of diagnostic importance.

Cecal Mucosal Myxoma: The First Report of a New Type of Mesenchymal Colon Polyp

Myxomas are benign mesenchymal neoplasms of unknown etiology that most commonly occur in the cardiac atrium; however, other reported sites include the skin, joints, skeletal muscles, maxillofacial bones, and sinonasal tract. Myxomas involving the gastrointestinal (GI) tract are rare and are limited to a few published case reports. We are presenting, to our knowledge, the first case report of a mucosal myxoma in the colon presenting as a colonic polyp. A 49-year-old woman underwent a screening colonoscopy and was found to have a 0.2-cm sessile polyp in the cecum. Histologically, the polyp was composed of bland spindled cells in the lamina propria set in a hypocellular, myxoid stroma. The lesion was relatively well-demarcated from the surrounding mucosa. The overlying colonic epithelium showed no dysplasia. S-100 immunohistochemical stain showed only focal nonspecific positivity, while CD34, CD117, SMA, EMA, and desmin were all negative. Alcian blue special stain showed positive staining, supporting the diagnosis of myxoma. Myxomas in the GI tract are very rare, with this being the first reported case of a polypoid colonic mucosal myxoma. Previous reports of GI myxomas are limited to examples in the stomach, small bowel, and one recently reported case in the colon, all of which were submucosal lesions and not limited to the mucosa. In some of the prior reports, the patients had synchronous cardiac atrial myxomas. Mucosal colonic myxoma represents a newly identified mesenchymal polyp of the colon and pathologists should be aware of this diagnostic entity.

A Colonic Perineurioma

Perineurioma is a mesenchymal neoplasm best known in soft-tissue pathology. A colonic perineurioma is a relatively recently described entity and sometimes encountered in specimens from the large intestine, especially distal colon. Without its recognition, a perineurioma can be misdiagnosed as other more common gastrointestinal spindle cell neoplasms. Here, we describe a case of colonic perineurioma with polypoid growth extruding into the intestinal lumen. Case. A woman in her seventh decade of life underwent a follow-up colonoscopy after an uneventful resection of a benign colonic polyp. A previously undetected 6-mm polyp was found in the sigmoid colon and was resected endoscopically. Microscopic examination of the lesion revealed a proliferation of bland spindle cells in the lamina propria mucosae, which were immunohistochemically positive for epithelial membrane antigen, claudin 1, and glucose transporter-1. A colonic perineurioma was diagnosed.

Telocytes are the physiological counterpart of inflammatory fibroid polyps and PDGFRA-mutant GISTs

PDGFRA mutations in the gastrointestinal (GI) tract can cause GI stromal tumour (GIST) and inflammatory fibroid polyp (IFP). Hitherto no cell type has been identified as a physiological counterpart of the latter, while interstitial Cajal cells (ICC) are considered the precursor of the former. However, ICC hyperplasia (ICCH), which strongly supports the ICC role in GIST pathogenesis, has been identified in germline KIT-mutant settings but not in PDGFRA-mutant ones, challenging the precursor role of ICC for PDGFRA-driven GISTs. Telocytes are a recently described interstitial cell type, CD34+/PDGFRA+. Formerly considered fibroblasts, they are found in many organs, including the GI tract where they are thought to be involved in neurotransmission. Alongside IFPs and gastric GISTs, GI wall "fibrosis" has been reported in germline PDGFRA-mutants. Taking the opportunity offered by its presence in a germline PDGFRA-mutant individual, we demonstrate that this lesion is sustained by hyperplastic telocytes, constituting the PDGFRA-mutant counterpart of germline KIT mutation-associated ICCH. Moreover, our findings support a pathogenetic relationship between telocyte hyperplasia and both IFPs and PDGFRA-mutant GISTs. We propose the term "telocytoma" for defining IFP, as it conveys both the pathogenetic (neoplastic) and histotypic ("telocytary") essence of this tumour, unlike IFP, which rather evokes an inflammatory-hyperplastic lesion.

Colonic perineurioma (benign fibroblastic polyp): case report and review of the literature

BACKGROUND

Colorectal perineuriomas are uncommon benign mucosal-based proliferations of mesenchymal cells that express perineurial markers, often associated with colonic crypts displaying a serrated/hyperplastic architecture. The vast majority of cases arise distal to the splenic flexure and have been described as sessile polyps. Using molecular analysis, BRAF mutations have been demonstrated in the serrated crypt epithelium. We report a new case of perineurioma presenting as a pedunculated polyp in the transverse colon, with prominent hemosiderin deposits in the uninvolved lamina propria that separated the perineurial proliferation from the surface epithelium, a previously unreported histological finding. By using immunohistochemistry, we demonstrated the presence of BRAF V600E mutated protein in the serrated crypt epithelium. In addition, a review of the literature on colorectal perineurioma is provided.

CASE PRESENTATION

A 5 mm pedunculated polyp was removed from the transverse colon of a 42 year old man who presented with epigastric pain, weight loss and rectal bleeding. A proliferation of uniform plump spindled cells expanded the lamina propria and separated serrated colonic crypts. The epithelial component closely resembled microvesicular hyperplastic polyp. Immunohistochemical stains for epithelial membrane antigen (EMA), glucose transporter 1 (GLUT1) and collagen IV were positive in the stromal proliferation. A mutation-specific monoclonal antibody directed against BRAF V600E showed positive cytoplasmic staining in the serrated crypt epithelium but not in the perineurial proliferation. Conspicuous hemosiderin deposition was seen in the inflamed lamina propria between the perineurial proliferation and the surface epithelium.

CONCLUSION

Although the majority of colorectal perineuriomas occur in the sigmoid colon and rectum and are described as sessile polyps, colorectal perineurioma can present as a pedunculated polyp proximal to the splenic flexure as described in this case. Conspicuous hemosiderin deposition can be seen in the superficial lamina propria. BRAF mutations are limited to the serrated crypt epithelium.

Neural and neurogenic tumours of the gastroenteropancreaticobiliary tract

Neural lesions occur uncommonly in the gastroenteropancreaticobiliary tract. However, due to the growing number of screening colonoscopy procedures, polypoid neural lesions of the colon are being recognised increasingly and range from benign tumours to high-grade malignant neoplasms. Morphological variability of neural tumours can be wide, although some entities share pathological features, and, as such, these lesions can be diagnostically challenging. We review the spectrum of pathology of neural tumours in the gastroenteropancreaticobiliary tract, with the goal of providing a practical approach for practising surgical pathologists.

Neurogenic polyps of the gastrointestinal tract: a clinicopathologic review with emphasis on differential diagnosis and syndromic associations

Primary neurogenic gastrointestinal polyps are encountered relatively frequently in routine pathology practice. They encompass a variety of neoplastic entities with clinical, morphologic, and molecular features that reflect the diversity of neural elements within the gastrointestinal system. Although most are benign and encountered incidentally, accurate diagnosis may have important clinical implications because of the associations of certain neurogenic polyps with familial syndromes or other conditions. We review the pathology of these polyps with an emphasis on the diagnostic challenges that they pose and on newly described subtypes.

Gastrointestinal tract spindle cell lesions--just like real estate, it's all about location

Interpretation of gastrointestinal tract mesenchymal lesions is simplified merely by knowing in which anatomic layer they are usually found. For example, Kaposi sarcoma is detected on mucosal biopsies, whereas inflammatory fibroid polyp is nearly always in the submucosa. Gastrointestinal stromal tumors (GISTs) are generally centered in the muscularis propria. Schwannomas are essentially always in the muscularis propria. Mesenteric lesions are usually found in the small bowel mesentery. Knowledge of the favored layer is even most important in interpreting colon biopsies, as many mesenschymal polyps are encountered in the colon. Although GISTs are among the most common mesenchymal lesions, we will concentrate our discussion on other mesenchymal lesions, some of which are in the differential diagnosis of GIST, and point out some diagnostic pitfalls, particularly in immunolabeling.

Perineurioma in the sigmoid colon diagnosed and treated by endoscopic resection

Perineuriomas are rare benign peripheral nerve sheath tumors in the gastrointestinal tract. We recently encountered a submucosal lesion in the sigmoid colon that was resected by endoscopic mucosal resection and was then diagnosed as perineurioma by immunohistochemistry. A 51-year-old female with a positive test for fecal occult blood was referred to our hospital for screening colonoscopy. Colonoscopy identified a submucosal lesion, approximately 15 mm in diameter, in the sigmoid colon. Endoscopic ultrasound showed a 15-mm tumor with a strong acoustic shadow. Endoscopic mucosal resection was performed in order to make a precise diagnosis as well as removal. The specimen revealed spindle cell proliferation without atypia, and immunostaining revealed that the spindle cells were positive for collagen type IV and glut-1, and the lesion was diagnosed as a colonic perineurioma with no malignancy. Gastroenterologists as well as pathologists should be aware of this type of submucosal lesion, and immunohistochemical evaluation is highly recommended when an unusual mesenchymal tumor is found.

Claudin-1 Expression Is Elevated in Colorectal Cancer Precursor Lesions Harboring the BRAF V600E Mutation

BACKGROUND: Sessile serrated adenomas/polyps (SSA/P) are now recognised precursors of colorectal cancer (CRC) including cancers harbouring somatic BRAF (V600E) mutations. While the morphological diagnostic criteria of SSA/P have been established, distinguishing between small/early SSA/P and microvesicular hyperplastic polyps (MVHP) is challenging and may not be possible in routine practice. METHODS: Gene expression profiling of MVHP (n=5, all BRAF V600E wild-type) and SSA/P (n=5, all BRAF V600E mutant) samples was performed. Quantitative reverse transcription–polymerase chain reaction (qRT-PCR) and immunohistochemical analysis was performed to verify the expression of claudin 1 (CLDN1) in MVHP and SSA/P. RESULTS: Gene expression profiling studies conducted between MVHP and SSA/P identified CLDN1 as the most statistically significant differentially expressed gene (p<0.05). Validation with qRT-PCR confirmed an up-regulation of CLDN1 in BRAF V600E mutant polyps regardless of polyp type (p<0.0005). Immunohistochemical analysis of CLDN1 expression in BRAF V600E mutant SSA/Ps (n=53) and MVHPs (n=111) and BRAF wild-type MVHPs (n=58), demonstrated a strong correlation between CLDN1 expression and the BRAF V600E mutation in both SSA/P and MVHP samples when compared to wild-type polyps (p<0.0001). CONCLUSION: This study demonstrates an up regulation of CLDN1 protein in serrated colorectal polyps including MVHP harbouring the BRAF V600E mutation. Our results demonstrated an apparent heterogeneity on the molecular level within the MVHP group and suggest that MVHP with somatic BRAF V600E mutation and up-regulated expression of CLDN1 are closely related to SSA/P and may in fact represent a continuous spectrum of the same neoplastic process within the serrated pathway of colorectal carcinogenesis.

Mesenchymal Tumors of the Gastrointestinal Tract Other than GIST

Mesenchymal tumors involve the gastrointestinal (GI) tract more frequently than other visceral organs. Many such tumors are small, and are benign and increasingly being detected incidentally during colonoscopic screening. Some tumors show distinctive features at this site, such as schwannoma and clear cell sarcoma-like tumor of the GI tract. Without knowledge of these features, recognition of these tumor types can be difficult. This reviews addresses recent developments and diagnostic features of mesenchymal tumors of the GI tract other than gastrointestinal stromal tumor (GIST).

Appendiceal Mucosal Schwann Cell Proliferation

Recognition of an appendiceal diverticulum is important because of its association with an appendiceal neoplasm. The incidence of mucosal Schwann cell proliferation in 24 cases of appendiceal diverticular disease, 17 serrated polyps, 4 cases of mucosal hyperplasia, and 45 normal appendices was determined. Ten (42%) of 24 cases with diverticula, 2 (50%) of 4 cases of mucosal hyperplasia with concurrent surface low-grade dysplasia, and 9 (20%) of 45 cases of normal appendices showed mucosal Schwann cell proliferation. It was not seen within the 17 cases of serrated polyps. Mucosal Schwann cell proliferation is common in appendiceal diverticular disease and may serve as a histologic marker for the presence of an appendiceal diverticulum. Thus, when routine histologic sections of a removed appendix demonstrate Schwann cell proliferation, further examination of the specimen may detect possible coexisting diverticular disease, which in turn may be associated with appendiceal neoplasms and epithelial dysplasia.

[Clinicopathologic features of colonic perineuriomas]

Intestinal perineuriomas are uncommon tumors of the gastrointestinal tract. In this study, we analyzed the clinicopathologic and immunohistochemical features of nine colonic perineuriomas. Five patients were women and four were men (median age 59.5 years and 64 years, respectively). All lesions were smaller than 1cm and were located intramucosally, mainly in the distal colon. Immunohistochemical techniques for Glut-1, claudin-1 and EMA were especially useful in characterizing these lesions.

Benign gastrointestinal mesenchymal BUMPS: a brief review of some spindle cell polyps with published names

CONTEXT

There are several benign, predominantly spindle cell, mesenchymal proliferations involving the mucosa and/or submucosa in the gut, which present as polyps and pathologists see as polypectomy specimens. These include perineuriomas, Schwann cell nodules, ganglioneuromas, leiomyomas of the muscularis mucosae, inflammatory fibroid polyps, and granular cell tumors.

OBJECTIVES

To evaluate these mesenchymal polyps for their morphologic, immunohistochemical, ultrastructural, and molecular characteristics and to determine some of their associations.

DATA SOURCES

Personal observations based on years of analyzing endoscopic biopsies and a review of the world's literature.

CONCLUSIONS

These polyps do surface every so often. There is significant literature covering inflammatory fibroid polyps and granular cell tumors, but there is little literature about the other entities.

Schwann cell hamartoma: case report

Background

Colorectal polyps of mesenchymal origin represent a small percentage of gastrointestinal (GI) lesions. Nevertheless, they are encountered with increasing frequency since the widespread adoption of colonoscopy screening.

Case presentation

We report a case of a small colonic polyp that presented as intramucosal diffuse spindle cell proliferation with a benign cytological appearance, strong and diffuse immunoreactivity for S-100 protein, and pure Schwann cell phenotype. Careful morphological, immunohistochemical and clinical evaluation emphasize the differences from other stromal colonic lesions and distinguish it from schwannoma, a circumscribed benign nerve sheath tumor that rarely arises in the GI tract.

Conclusion

As recently proposed, this lesion was finally described as mucosal Schwann cell hamartoma.

Gastrointestinal Mesenchymal Neoplasms other than Gastrointestinal Stromal Tumors: Focusing on Their Molecular Aspects

Gastrointestinal (GI) mesenchymal tumors other than gastrointestinal stromal tumor (GIST) are rare neoplasms, but they often enter the differential diagnosis of more common GI lesions. Some of these mesenchymal tumors in the GI tract have well understood molecular pathologic aspects, including desmoid tumors, inflammatory myofibroblastic tumor (IMT), clear cell sarcoma (CCS), inflammatory fibroid polyp (IFP), and synovial sarcoma (SS). Molecular pathology is fast becoming a mainstream focus in laboratories because it aids in the precise classification of tumors, may be prognostic, and may help predict response to therapy. The following review is not intended as an exhaustive summary of all mesenchymal tumors that have been reported to involve the GI tract, but instead will highlight the current knowledge of the most important non-GIST GI mesenchymal neoplasms, focusing on those tumors with well-characterized molecular pathology and how the molecular pathologic features impact current diagnostic, therapeutic, and prognostic standards.

Benign serrated colorectal fibroblastic polyps/intramucosal perineuriomas are true mixed epithelial-stromal polyps (hybrid hyperplastic polyp/mucosal perineurioma) with frequent BRAF mutations

Colorectal fibroblastic polyp and intramucosal perineurioma are 2 synonyms for a recently described benign mucosal lesion with a predilection for the rectosigmoid colon. These lesions are characterized by aggregates of bland spindled cells separating and distorting mucosal crypts. The latter frequently showed a serrated architecture. The pathogenesis of fibroblastic polyp/intramucosal perineurioma and the nature of serrated crypts observed in them are poorly understood. We analyzed the clinicopathological features of 29 fibroblastic polyps and investigated them for the first time for mutations known to be involved in serrated colorectal epithelial polyps (BRAF, KRAS, and PIK3CA). Patients were 23 women and 6 men with a mean age of 64 years (range: 47 to 84 y). All lesions represented asymptomatic solitary polyps (mean size 3.5 mm) localized predominantly in the rectosigmoid colon (81%). Hyperplastic polyps, classical adenoma, and sessile serrated adenoma/lesion coexisted in 12 (44%), 12 (44%), and 5 (17%) patients, respectively. All lesions showed irregular aggregates of bland spindled cells separating and distorting mucosal crypts. Serrated (hyperplastic) crypts were observed on the top or contiguous with the lesion in all cases. Immunohistochemistry revealed expression of at least one perineurial cell marker (epithelial membrane antigen, claudin-1, and glucose transporter-1) in 26 out of 27 lesions (96%), but expression of CD34 was less common (8 of 27; 30%). Immunostaining for hMLH1 showed a normal nuclear expression. Molecular analysis in 22 cases showed V600E BRAF mutation in 14 cases (63%) and KRAS mutation in 1 (4%). The remainder were wild-type for all 3 genes. Our results indicate that serrated fibroblastic polyps/intramucosal perineuriomas represent a unique type of mixed epithelial-stromal polyps (hybrid hyperplastic polyp/mucosal perineurioma). The perineurial stromal component might be derived from modified pericryptic fibroblasts as a consequence of a yet poorly understood epithelial-stromal interaction.

Serrated Colorectal Neoplasia

Until very recently, there was general acceptance in the pathology community that all serrated lesions of the colon and rectum without overt cytologic dysplasia were hyperplastic polyps and had no malignant potential. Although there are still several unanswered questions in regard to the relationship between the various serrated lesions, there is a better understanding of the relationship of sessile serrated adenoma to carcinoma. This article discusses hyperplastic polyps, sessile serrated adenoma, traditional serrated adenoma, mixed polyps, and serrated lesions in such conditions as idiopathic inflammatory bowel disease and mechanical trauma. The major focus of the content is on diagnostic features of these lesions.

Pseudoneoplasms of the gastrointestinal tract

CONTEXT

The pathologist plays the leading role in distinguishing pseudoneoplasms from truly neoplastic lesions in the gastrointestinal tract.

OBJECTIVE

This review was conducted to heighten awareness of pseudoneoplasms, to help differentiate among the various types of pseudoneoplasms, and to help distinguish pseudoneoplasms from malignancies.

DATA SOURCES

This review is based on the medical literature on pseudoneoplasms in MEDLINE and the authors' own experiences. Reference lists of retrieved articles were also reviewed to identify additional articles.

CONCLUSIONS

A classification of pseudoneoplasms, according to the mechanism of injury to the gastrointestinal tract, morphologic patterns, and heterotopia, may be useful in providing a diagnostic framework in which ancillary techniques often have a diagnostic role. Several pseudoneoplasms may be closely associated with true neoplasms (eg, malakoplakia, prolapsetype lesions) because of the nonspecific nature of the response of the intestine to injury.

Myxoid perineurioma presenting as a gastric polyp

A 58-year-old man presented with epigastric pain that was refractory to analgesia. Before this, he was well and did not have manifestations of type 1 neurofibromatosis. Endoscopy revealed a 0.5-cm polypoid antral lesion that was snared and removed in total. Histological evaluation showed a submucosal myxoid spindle-cell proliferation. The tumor was arranged in whorls with distinct concentricity. Within the myxoid stroma, occasional eosinophils were present together with a delicate capillary network. There was no cytological atypia, areas of hypercellularity, or necrosis. The lesion was strongly positive for epithelial membrane antigen and also positive for CD34. All other markers including S-100, desmin, and CD117 were negative. The overall morphological and immunophenotypic features of this lesion are in keeping with a myxoid gastric perineurioma. This lesion needs to be separated from an inflammatory fibroid polyp and a gastrointestinal stromal tumor.

Peripheral nerve sheath tumors of the gastrointestinal tract: a multicenter study of 58 patients including NF1-associated gastric schwannoma and unusual morphologic variants

The frequency and morphological spectrum of gastrointestinal peripheral nerve sheath tumors (PNSTs) from consecutive case material has not been studied in the c-KIT era. We reviewed all mesenchymal gastrointestinal (GI) lesions at our departments according to current diagnostic criteria. PNSTs formed the third commonest group of mesenchymal GI tumors with a lower frequency (< or =5%) compared to gastrointestinal stromal tumors (GISTs; approximately 50%) and smooth muscle neoplasms ( approximately 30%). Granular cell tumors (GCTs; n = 31) and schwannomas (n = 22) were the most common types of PNSTs encountered. Rare tumors included neurofibromatosis 1 (NF1)-associated PNSTs (n = 5) and gastric perineurioma (n = 1). Thirteen schwannomas (including also some recent cases) were initially diagnosed as GIST, leiomyoma, or neurofibroma. Unusual histological variants included sigmoid GCT with prominent lipomatous component (n = 1), reticular-microcystic schwannoma of small (n = 1) and large (n = 1) bowel, NF1-associated gastric schwannoma (the first case to date), and psammomatous melanotic colonic schwannoma unrelated to Carney complex (n = 1). PNSTs coexisted with GIST in four patients (three had definite NF1). In conclusion, PNSTs of the GI tract are rare uniformly benign neoplasms that may show schwannian, perineurial, fibroblastic, or mixed differentiation. Most of them (92%) occurred sporadically unassociated with NF1 or NF2. Gastrointestinal PNSTs are still underrecognized by general pathologists. Awareness of their diverse morphology will help to avoid confusing them with smooth muscle neoplasms and GIST that they may closely mimic.

Early Colonic Perineurioma: A Report of 11 Cases

Colonic perineurioma has been depicted as characterized by a mucosal proliferation of monomorphic spindle perineurial cells leading to an evident separation, distortion, and entrapment of colonic crypts. The authors, however, believe that a sizable subset of the cases differ in that they display only a limited perineurial proliferation leading to only mild crypt separation without crypt entrapment. This morphological variant (early perineurioma) has not yet been documented. The authors herein present the clinicopathological and immunohistochemical features of 11 cases. Polyp size ranged from 2 to 4 mm, and 8 (73%) were located in the sigmoid. Histologically, they revealed small, frequently noncontiguous nests or bundles of uniform round to oval cells, causing slight separation of parallel or mildly distorted crypts, which displayed a serrated/hyperplastic architecture in 8 (73%) cases. Immunostaining for perineurial markers showed strong expression for claudin-1, GLUT-1, and collagen type IV and weak reactivity for epithelial membrane antigen. In conclusion, early perineurioma is a morphological variant of colonic perineurioma in which the perineurial proliferation is limited and consequently more difficult to recognize. Using perineurial markers is helpful in reaching an accurate diagnosis.

Benign fibroblastic polyps of the colon

Benign fibroblastic polyps of the colon are a recently described entity among mucosal polyps found in the colorectum. These polyps are typically discovered on routine screening colonoscopy within the distal colon. Benign fibroblastic polyps occur most commonly in adult women in the sixth decade of life. Histologically, benign fibroblastic polyps are bland spindle cell lesions that fill the lamina propria and displace the surrounding crypts. The spindle cell proliferation lacks atypia and significant mitotic activity. Hyperplastic changes are frequently present both in the adjacent epithelium and within the lesions. Immunohistochemically, the cells of benign fibroblastic polyps are invariably positive for vimentin with rare focal positivity for CD34 and smooth muscle actin. They are negative for CD117 and S100 protein. Ultrastructurally, benign fibroblastic polyps have features of fibroblastic differentiation. These polyps are benign with no reports, to our knowledge, of recurrence or metastasis.

Mucosal Schwann cell "hamartoma": clinicopathologic study of 26 neural colorectal polyps distinct from neurofibromas and mucosal neuromas

Colorectal polyps containing S-100-positive neural proliferations in the lamina propria that lack ganglion cells have been variously referred to as "neuromas" or "neurofibromas." However, these lesions have not been systematically examined, and whether they are associated with type 1 neurofibromatosis (NF1) or other inherited syndromes is unknown. The aim of this study was to evaluate the clinicopathologic and immunohistochemical features of these lesions, in comparison to colorectal neurofibromas from known NF1 patients. Morphologically similar lesions from 26 patients (mean age, 62 y; range, 46 to 88 y; male/female ratio, 10/16) were retrieved from surgical pathology and consult files. Clinical and endoscopic data were obtained, and immunohistochemistry for S-100 protein, glial fibrillary acidic protein, neurofilament protein (NFP), epithelial membrane antigen, claudin-1, CD34, smooth muscle actin, and KIT was performed. The findings were compared with those in mucosal biopsies of 5 submucosal neurofibromas from NF1 patients. All 26 polyps were sessile, ranging from 1 to 6 mm in size (mean, 2.5 mm). Most arose in the distal colon (15 rectosigmoid, 7 descending, 2 transverse, and 2 ascending), and were incidentally found at screening colonoscopy. After a mean follow-up of 6.5 years (range, 3 mo to 17.5 y), none of the patients developed other neural polyps, and none had evidence of NF1 or other inherited syndromes. Histologically, the lamina propria of the polyps contained a diffuse cellular proliferation of uniform bland spindle cells with elongated, tapering nuclei, abundant, dense eosinophilic cytoplasm, and indistinct cell borders, entrapping adjacent crypts. No nuclear atypia, pleomorphism, mitotic activity, or associated ganglion cells were observed. All showed strong staining for S-100 protein in essentially 100% of cells. NFP highlighted rare axons in 7 lesions. All other markers were negative. The 5 neurofibromas showed similar histologic features, but were generally less uniformly cellular, showed some intralesional heterogeneity, and showed less extensive staining for S-100 protein; all contained scattered NFP-positive axons. In summary, solitary colorectal polyps containing pure Schwann cell proliferations in the lamina propria are not associated with NF1. Distinguishing these lesions from NF1-associated neurofibromas is difficult based on histologic features; the presence of an underlying submucosal nodule or mass should be excluded endoscopically, and immunohistochemistry should be performed. Although their nature is uncertain, we propose the interim designation "mucosal Schwann cell 'hamartoma'" to avoid confusion with the neural lesions that have significant associations with inherited syndromes.