MRI and Biologic Behavior of Desmoid Tumors in Children

Imaging-Based Deep Learning for Predicting Desmoid Tumor Progression

Desmoid tumors (DTs) are non-metastasizing and locally aggressive soft-tissue mesenchymal neoplasms. Those that become enlarged often become locally invasive and cause significant morbidity. DTs have a varied pattern of clinical presentation, with up to 50-60% not growing after diagnosis and 20-30% shrinking or even disappearing after initial progression. Enlarging tumors are considered unstable and progressive. The management of symptomatic and enlarging DTs is challenging, and primarily consists of chemotherapy. Despite wide surgical resection, DTs carry a rate of local recurrence as high as 50%. There is a consensus that contrast-enhanced magnetic resonance imaging (MRI) or, alternatively, computerized tomography (CT) is the preferred modality for monitoring DTs. Each uses Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1), which measures the largest diameter on axial, sagittal, or coronal series. This approach, however, reportedly lacks accuracy in detecting response to therapy and fails to detect tumor progression, thus calling for more sophisticated methods. The objective of this study was to detect unique features identified by deep learning that correlate with the future clinical course of the disease. Between 2006 and 2019, 51 patients (mean age 41.22 ± 15.5 years) who had a tissue diagnosis of DT were included in this retrospective single-center study. Each had undergone at least three MRI examinations (including a pretreatment baseline study), and each was followed by orthopedic oncology specialists for a median of 38.83 months (IQR 44.38). Tumor segmentations were performed on a T2 fat-suppressed treatment-naive MRI sequence, after which the segmented lesion was extracted to a three-dimensional file together with its DICOM file and run through deep learning software. The results of the algorithm were then compared to clinical data collected from the patients' medical files. There were 28 males (13 stable) and 23 females (15 stable) whose ages ranged from 19.07 to 83.33 years. The model was able to independently predict clinical progression as measured from the baseline MRI with an overall accuracy of 93% (93 ± 0.04) and ROC of 0.89 ± 0.08. Artificial intelligence may contribute to risk stratification and clinical decision-making in patients with DT by predicting which patients are likely to progress.

Selective Intra-Arterial Doxorubicin Eluting Microsphere Embolization for Desmoid Fibromatosis: A Combined Prospective and Retrospective Study

Simple Summary

Desmoid fibromatoses (DFs) are locally aggressive tumors composed of monoclonal fibroblasts within an abundant extracellular matrix. Systemic treatment with doxorubicin is effective, but associated with significant toxicity. We investigated arterial doxorubicin eluting embolization (DEE), an approach that delivers high doxorubicin concentrations to the tumor with limited systemic drug exposure, in 24 patients (median age, 24 years; interquartile range, 16–34). Most patients (71%) had one or more than one prior DFs treatment (surgery, systemic therapy, or both). Patients underwent a median of two (range, 1–4) DEE treatments, with a median of 49 mg (range, 8–75) doxorubicin per treatment. Efficacy outcomes were available for 23 patients. With a median follow-up of 8 months (interquartile range, 3–13), median tumor volumes decreased by 59% (interquartile range, 40–71%). Of 23 patients, 9 (39%), 12 (52%), and 2 (9%) had a partial response, stable disease, and progressive disease, respectively. The procedure was safe and well tolerated.

Abstract

Desmoid fibromatoses (DFs) are locally aggressive tumors composed of monoclonal fibroblasts within an abundant extracellular matrix. Systemic doxorubicin treatment is effective, but toxic. We investigated arterial doxorubicin eluting embolization (DEE), an approach characterized by high drug concentrations in the tumor alongside limited systemic drug exposure. The primary and secondary endpoints were radiological response using MRI and RECIST 1.1, respectively. The study included 24 patients (median age, 24; interquartile range, 16–34 years). Data were collected prospectively for 9 patients and retrospectively for 15 patients. The most frequent tumor locations were chest/abdomen wall and neck/shoulder/axilla (29% each). Of 24 patients, 7 (24%) were treatment naïve, and 17 (71%) had received one or two prior treatments. Patients underwent a median of two treatments (range, 1–4), with a median of 49 mg (range, 8–75) doxorubicin/treatment. Efficacy outcomes were available for 23 patients. With a median follow-up of 8 months (interquartile range, 3–13), median tumor volumes decreased by 59% (interquartile range, 40–71%) and T2 signal intensity decreased by 36% (interquartile range, 19–55%). Of 23 patients, 9 (39%), 12 (52%), and 2 (9%) had a partial response, stable disease, and progressive disease, respectively. DEE was safe and well tolerated, with one reported grade 3–4 adverse event (cord injury). In conclusion, DEE was safe and achieved rapid clinical/volumetric responses in DFs.

The Role of Pharmacotherapeutic Agents in Children with Desmoid Tumors

Desmoid tumors (DT) are rare fibroblastic, soft-tissue tumors that do not metastasize but can aggressively infiltrate tissues causing significant chronic discomfort and/or functional impairment. In the pediatric population, the incidence of DT is greatest during infancy and adolescence but can occur at any age. Dysregulated β-catenin, most commonly resulting from mutations in either CTNNB1 or germline APC (adenomatous polyposis coli) drives DT. Most cases are sporadic but some are associated with predisposition syndromes such as familial adenomatous polyposis (FAP). Historically, treatment has been surgery. However, the recurrence rate after surgery can be high. Various systemic cytotoxic chemotherapy regimens used in other soft-tissue sarcomas have been applied to DT with differing results. Given the chronic and rarely life-threatening nature of this disease and the potential short- and long-term toxicity of these regimens, especially in children, alternative non-cytotoxic interventions have been investigated. Molecularly targeted agents such as tyrosine kinase and gamma secretase inhibitors have shown activity against DT. Innovative local control therapies are being employed as alternatives to surgery and radiation. Periods of prolonged stability and spontaneous regression in the absence of therapy in some patients has prompted wider adoption of an upfront active surveillance approach in the appropriate setting. This review will briefly summarize the epidemiology, pathophysiology, and clinical presentation of DT in children, then focus on historical, current, and future pharmacotherapeutic management and finally, propose areas for future study.

Imaging findings of familial adenomatous polyposis-associated aggressive mesenteric fibromatosis: A case report

Introduction. Aggressive fibromatosis, also known as desmoid type fibromatosis (DF) is a locally aggressive fibroblastic neoplasm that can arise anywhere in the body with no potential for metastasis and a high recurrence rate after surgical resection. Mesenteric fibromatosis are locally aggressive DF of the mesentery with a high propensity for bowel involvement. The real etiology of these tumors remains unknown, occurring sporadically or in association with familial adenomatous polyposis (FAP), as Gardner?s syndrome. Case report. A 34-year-old female patient presented with a palpable solid tumefactive mass in the left hemiabdomen. Contrast enhanced computed tomography (CT) and magnetic resonance imaging (MRI) revealed multiple massive solid tumefactions in the mesentery and in between the small bowel loops. Colonoscopy confirmed the presence of multiple sessile polyps characteristic of FAP. Tissue samples of the mesenteric mass were acquired via ultrasound guided biopsy with histopathologic confirmation of desmoid fibromatosis with imunohistochemical analysis. The risk of surgery was deemed too high at the time due to the size of the mass and proximity to mesenteric vascular structures, therefore the patient was planned for chemotherapy with a potential for further surgical reevaluation. Conclusion. Mesenteric fibromatosis is a rare neoplasm that presents with a wide range of histologic and imaging features. CT and MRI play a crucial role in evaluation and planning an optimal treatment model for patients with mesenteric fibromatosis.

CRISPR-SID: Identifying EZH2 as a druggable target for desmoid tumors via in vivo dependency mapping

Cancer precision medicine implies identification of tumor-specific vulnerabilities associated with defined oncogenic pathways. Desmoid tumors are soft-tissue neoplasms strictly driven by Wnt signaling network hyperactivation. Despite this clearly defined genetic etiology and the strict and unique implication of the Wnt/β-catenin pathway, no specific molecular targets for these tumors have been identified. To address this caveat, we developed fast, efficient, and penetrant genetic Xenopus tropicalis desmoid tumor models to identify and characterize drug targets. We used multiplexed CRISPR/Cas9 genome editing in these models to simultaneously target a tumor suppressor gene (apc) and candidate dependency genes. Our methodology CRISPR/Cas9 selection-mediated identification of dependencies (CRISPR-SID) uses calculated deviations between experimentally observed gene editing outcomes and deep-learning-predicted double-strand break repair patterns to identify genes under negative selection during tumorigenesis. This revealed EZH2 and SUZ12, both encoding polycomb repressive complex 2 components, and the transcription factor CREB3L1 as genetic dependencies for desmoid tumors. In vivo EZH2 inhibition by Tazemetostat induced partial regression of established autochthonous tumors. In vitro models of patient desmoid tumor cells revealed a direct effect of Tazemetostat on Wnt pathway activity. CRISPR-SID represents a potent approach for in vivo mapping of tumor vulnerabilities and drug target identification.

A Novel Method to Treat Progressive Desmoid Tumors Involving Neurovascular Bundles: A Retrospective Cohort Study

BACKGROUND

More effective therapies are needed to treat progressive desmoid tumors when active surveillance and systemic therapy fail.

OBJECTIVE

To assess the efficacy and safety of sandwich isolation surgery on the local control of progressive desmoid tumors involving neurovascular bundles.

METHODS

A total of 27 patients with progressive desmoid tumors at extremities involving neurovascular bundles who received surgery at our hospital between August 2014 and August 2018 were identified. A total of 13 patients received sandwich isolation surgery, in which R2 resection was performed in neurovasculature-involving regions, and a biomaterial patch was used to envelop involved neurovascular structures and isolate residual tumors. In non-neurovasculature-involving regions, wide resection was performed without isolation. A total of 14 patients received traditional surgery, which included tumor resection without isolation procedure.

RESULTS

In sandwich isolation group, tumor progressions and local recurrences occurred in 3 patients outside the isolated neurovasculature-involving regions. However, no progressions or recurrences occurred in any patients in the isolated neurovasculature-involving regions where R2 resection was performed. Sandwich isolation surgery group and traditional surgery group shared similar baseline clinical characteristics. The estimated 3-yr event-free survival rate was 76.9% after sandwich isolation surgery, and 32.7% after traditional surgery (P = .025). Patients who received sandwich isolation surgery were less likely to have local recurrence (hazard ratio: 0.257, P = .040). No complications were noted except intermittent mild pain in operative regions (2 cases).

CONCLUSION

Sandwich isolation surgery is effective and safe for local control of desmoid tumors involving neurovascular bundles.

Radiological evaluation of deep soft tissue fibromatosis, the characteristic MR criteria on conventional and corresponding diffusion-weighted images

Background

To analyze the characteristic features of deep fibromatosis on conventional and diffusion-weighted MR images.

Result

The lesions were growing along the musculoaponeurotic fascia, mostly invaded the muscles, and showed ill-defined margins, low T2 signal bands and areas, and facial tail sign. Diffusion images showed mostly high or high mixed with low signal; only 2 lesions showed a persistent low signal. The average mean and minimum ADC values were 1.41 ± 0.26 × 10−3 mm2/s and 0.79 ± 0.43 × 10−3 mm2/s respectively. Post-contrast and DWI detected synchronous lesions and extensions missed on T1 and T2 images.

Conclusion

The most frequent MR features of deep fibromatosis are low T2 signal bands and areas, fascial tail sign, ill or partially defined margins, and predominant restricted diffusion pattern in addition to areas of “T2-blackout effect.” Post-contrast and DWI are more valuable in local staging of the tumor.

Imaging spectrum of mesenteric masses

Mesenteries are extensions of the visceral and parietal peritoneum consisting of fat, vessels, nerves, and lymphatics. Mesenteric masses have a wide differential diagnosis with neoplastic, infectious, or inflammatory etiologies and can either be solid or cystic. Imaging features are critical for the diagnosis. We review the epidemiology, imaging spectrum, and differentiating features and treatment of mesenteric masses.

Pazopanib therapy for desmoid tumors in adolescent and young adult patients

BACKGROUND

Desmoid tumors/aggressive fibromatosis (DT/AF) lack a reliably effective medical therapy. Surgical resection may be morbid and does not preclude recurrence. Radiation may carry severe late effects, particularly detrimental in young patients. At our institution, we recently observed promising results with pazopanib therapy for DT/AF in adolescent and young adult (AYA) patients.

PROCEDURE

Retrospective single-institution chart review.

RESULTS

Six DT/AF patients of 3-21 years with previously treated DT/AF received pazopanib; 31 DT/AF patients received established therapies only. In both groups, median age at diagnosis was 16 years, female patients comprised 50%, and most common DT/AF site was extremity. Established therapies showed few objective responses and most patients therefore received multiple therapies. Surgical resection had a 68% recurrence rate. Of eight patients who received vinblastine/methotrexate, only one had a partial response (PR) by RECIST 1.1 and five had stable disease (SD); 62.5% required additional therapy. Of seven patients who received sulindac/tamoxifen, none showed objective improvement. In contrast, pazopanib demonstrated best responses by RECIST of PR in two of seven and SD in six of seven tumors. A PR of 66% was observed in a patient who had failed multiple prior therapies. The mesenteric DT/AF also showed PR. Maximum volumetric decrease by T2-weighted magnetic resonance imaging (MRI) was 97%. Dramatically increased fibrosis was seen on T2-weighted MRI. Patients reported pain relief and improvement in function within 1 month. Except for one case of edema, all other toxicities responded to dose reduction without sacrificing objective treatment response.

CONCLUSION

Pazopanib provides a promising, well-tolerated therapy for DT/AF in the AYA population and warrants further study.

The Clinical and Radiological Characteristics of Inflammatory Myofibroblastic Tumor Occurring at Unusual Sites

Inflammatory myofibroblastic tumor (IMT) can occur rarely in the soft tissue or joint of the limb. We retrospectively collected IMT cases of these rare sites and analyzed their clinical and imaging appearance. Thirteen cases of IMT were clinically diagnosed and underwent surgical procedures, pathological analyses, and postsurgical follow-up in our two hospitals. Other than one case of IMT of the bladder wall that presented with gross hematuria, none presented with local swelling, fever, or weakness. All the cases of IMT occurring at the bone showed destruction and parosteal soft tissue masses. The boundaries between the mass and normal bone were vague, without calcifications or any periosteal reaction. Five cases of IMF showed continuous enhancement on CT; seven cases demonstrated iso- or hyposignal intensity on T1WI; one case showed hypersignal intensity on T1WI, and eight cases demonstrated a hypersignal intensity signal on T2WI. All the masses located in soft tissues showed clear and sharp boundaries with different sizes of the swelling regions surrounding muscle interspaces. Three cases showed homogeneous enhancement, one case demonstrated heterogeneous enhancement, and two cases showed edge enhancement on enhanced MRI scans. On pathology, all the lesions showed an absence of a pseudocapsule, and four cases of ALK were positive. The radiological manifestations of IMT located at the soft tissue and bones were similar to benign tumors in shape; however, peritumoral edema, parosteal soft tissue, and the invasive rim of IMT are similar to the features of malignant tumors. Different radiological methods should be used to obtain an accurate diagnosis.

Diagnostic imaging and CEUS findings in a rare case of Desmoid-type fibromatosis. A case report

Desmoid-type fibromatosis (DF), also known as aggressive fibromatosis, is a locally aggressive benign fibroblastic neoplasm that can infiltrate or recur but cannot metastasize. It is rare, with an estimated annual incidence of two to four new cases per million people. Most DFs occur sporadically, but it may also be associated with the hereditary syndrome familial adenomatous polyposis. Treatment is necessary when the disease is symptomatic, especially in case of compression of critical structures. When possible, surgical resection is the treatment of choice; however, recurrence is common. Due to the high rate of recurrence, imaging plays an important role not only in diagnosis, but also in the management of DF. Although there are a number of studies describing CT and MRI findings of DF, there is no description of contrast-enhanced ultrasound findings.

MRI may be used as a prognostic indicator in patients with extra-abdominal desmoid tumours

OBJECTIVE

To determine the association of MRI features of extra-abdominal desmoid tumours (DTs) with prognosis.

METHODS

MRIs for 90 patients with DT were retrospectively reviewed for imaging features associated with biological behaviour. The primary end point was progression (for lesions managed with chemotherapy, radiation therapy and observation) or recurrence (following surgery). Time to event was studied using univariate and multivariable Cox proportional hazards regression models when accounting for demographic, clinicopathological and imaging variables. Kaplan-Meier plots were used to estimate event-free rate (EFR).

RESULTS

Univariate analysis revealed a significant relationship between EFR and treatment, location and compartment of origin [subcutaneous (SC), superficial fascial, intramuscular (IM) and deep fascial/intermuscular]. None of the imaging features commonly associated with biological behaviour of DTs (e.g., shape, enhancement, T2 signal etc.) or surgical margins (in surgical cases) was associated with EFR. Multivariate analysis showed that treatment modality and compartment of origin were independent predictors of EFR. Superficial and deep fascial lesions had a significantly worse EFR as a group [hazard ratio: 3.9; 95% confidence interval (CI): 1.83-8.32; p = 0.0004] than did the SC and IM lesions as a group. 5-year EFR for the fascial lesions was 18% (95% CI: 6-36%), compared with 57% (95% CI: 25-79%) for the SC and IM groups.

CONCLUSION

Intramuscular or SC DTs may be associated with improved prognosis. If validated on multireader and prospective studies, these results can provide for rapid risk stratification at the time of initial MRI.

ADVANCES IN KNOWLEDGE

This work has shown that imaging features commonly associated with biological activity of desmoid tumours (e.g. shape, T2 signal and enhancement) do not appear to be associated with prognosis in patients undergoing a variety of treatment modalities. The compartment of origin of the lesion, which can be determined on pre-operative MRI, was shown to be associated with prognosis and can allow for risk stratification in patients with DTs.

MRI and CT of Low-Grade Fibromyxoid Sarcoma in Children: A Report From Children's Oncology Group Study ARST0332

OBJECTIVE

The purpose of this article is to determine the MRI and CT features of low-grade fibromyxoid sarcoma in children.

MATERIALS AND METHODS

We retrospectively analyzed images of 11 pediatric patients with low-grade fibromyxoid sarcoma from a phase 3 clinical trial of nonrhabdomyosarcoma soft-tissue sarcoma (Children's Oncology Group Protocol ARST0332). MRI and CT were performed in 10 and four patients, respectively. Location, size, margin, and composition on imaging were correlated with pathologic findings.

RESULTS

Tumors were located in the extremities in nine patients, and one tumor each was located in the tongue and lung. Tumors were deep in seven patients and superficial in four patients. All tumors were well defined, solitary, and nonmetastatic at presentation. Tumors were complex solid-cystic in eight patients and completely solid in three patients. On T1-weighted images, all tumors had at least some areas hypointense to muscles, and six had a split-fat sign. On STIR or T2-weighted images, eight tumors had areas hypointense to adjacent muscle, and eight tumors had fluid signal intensity. On contrast-enhanced MRI studies, eight tumors had thick enhancing internal septations, and three had peripheral nodular gyriform enhancement. When we correlated imaging to pathologic findings, areas with hypointense signal intensity on both T1- and T2-weighted images were likely related to fibrous component; areas with fluid signal intensity on T2-weighted images were likely related to myxoid component. On CT, all four tumors were hypodense to muscle, and one tumor showed punctate calcific foci.

CONCLUSION

Low-grade fibromyxoid sarcoma is hypodense to muscle on CT. MRI may identify both fibrous and myxoid components of this rare pediatric soft-tissue sarcoma.

Imaging of childhood inflammatory myofibroblastic tumor

BACKGROUND

Inflammatory myofibroblastic tumor is a rare benign neoplasm and most commonly involves the lung but occurs in extrapulmonary locations.

OBJECTIVE

To present imaging findings in inflammatory myofibroblastic tumors in children based on a single-centre experience.

MATERIALS AND METHODS

We retrospectively reviewed CT and MRI findings of children diagnosed with inflammatory myofibroblastic tumor in a single institution.

RESULTS

We identified 15 children (range: 1-17 years) with inflammatory myofibroblastic tumor. The tumor was localized to the lung (n = 5), mediastinum (n = 3), trachea (n = 1), bronchus (n = 1), abdomen (n = 2) and orbit (n = 3). All the extraorbital tumors were solid masses with homogeneous or heterogeneous enhancement. Four lung tumors and one posterior mediastinal tumor contained calcification. Local recurrence following surgical removal occurred in two children with invasion of the esophagus and of the left atrium in one. Localized masses were seen in all children with orbital tumour. Two of these had episcleritis and perineuritis; one had episcleritis, tendonitis, perineuritis, myositis and dacryoadenitis.

CONCLUSION

The locations and imaging features of inflammatory myofibroblastic tumors are variable.

Desmoid tumors of the head and neck: a therapeutic challenge

Desmoid tumor, or aggressive fibromatosis, is a rare, histologically benign, fibroblastic lesion that infrequently presents in the head and neck. Desmoid tumors often grow locally, invasively, and may, in rare instances, be fatal secondary to invasion into critical structures, such as airway or major vessels. The most common treatment is surgery, but desmoid tumors are characteristically associated with a high local recurrence rate after resection. Although the margin status seems to be of importance, operations that avoid function loss and esthetic disfigurement should be the primary goal. The efficacy of postoperative radiotherapy is controversial. Its potential benefit should be carefully balanced against possible radiation-induced adverse effects. Alternative treatment modalities, such as primary radiotherapy and medical treatment or a wait-and-see policy, may be preferable to mutilating surgery. Considering all the aforementioned, it seems obvious that desmoid tumors of the head and neck present a therapeutic challenge and require an individualized approach.

Magnetic resonance imaging of hip tumors

After initial evaluation with radiography, magnetic resonance (MR) imaging is the most common modality used to establish the diagnosis and characterize osseous and soft tissue tumors of the hip. Tumors involving the proximal femur are often benign, and MR imaging can be specific in diagnosing solitary bone cyst, osteochondroma, and chondroblastoma. Benign and malignant soft tissue tumors about the hip are often nonspecific in their MR imaging appearances, but knowledge of the patient's age may direct a more limited differential diagnosis. In the setting of malignancy, MR imaging is commonly used to stage tumors and follow patients postoperatively.

Early experience with percutaneous cryoablation of extra-abdominal desmoid tumors

OBJECTIVE

Surgical resection, radiation therapy and chemotherapy are all accepted as standard treatments for extra-abdominal desmoid (EAD) tumors, but their effectiveness has been limited by frequent local recurrence. The purpose of this article is to describe our early experiences with using percutaneous cryoablation for local control of extra-abdominal desmoid tumors in five patients whose tumors had failed to respond to standard therapy.

MATERIAL AND METHODS

In a retrospective search of our institution's radiology database for patients who had undergone percutaneous cryoablation for treatment of EAD tumors between June 2004 and July 2007, we identified five patients (three female and two male). No patients were excluded from this review. Three of these patients had been referred for cryoablation for local tumor control, and two had been referred for palliation of inoperable tumors. The age range of the patients at the time of cryoablation was 9-41 years. The treated EAD tumors were located in the neck, shoulders and trunk and ranged in size from 3.0 cm to 10.0 cm. Medical records were reviewed for short-term and long-term follow-up, and patients were contacted for additional follow-up. Patients were asked to rate their pain as absent, mild, moderate or severe, and to compare it with their levels before cryoablation, describing it as improved, unchanged or worsened. Radiology records were reviewed to follow the size of the EAD tumors before and after cryotherapy.

RESULTS

For the three patients referred for local control of EAD tumors, complete tumor coverage with the ablation zones was achieved. Two of these patients, with masses 3.0 cm and 4.9 cm in diameter, reported complete absence of pain at both short-term and long-term follow-up at 13 months and 49 months. Their tumors had completely resolved on long-term imaging follow-up at 19 months and 43 months. The third patient, with a 6.1 cm mass, reported improved mild pain at 6 months, and imaging showed a moderate decrease of tumor size. For the two patients referred for palliative therapy, initial partial pain relief was felt 2 weeks after the procedure, At long-term (58 months) follow-up of one patient with a 9.1 cm mass, the tumor was still present although reduced in size, and local pain had returned to its former moderate level. In the other patient who underwent only partial treatment of a 10.0 cm mass, at long-term follow-up (36 months) the mass had enlarged and pain had returned to the pretreatment, moderate level.

CONCLUSION

Cryoablation appears to be an effective alternative treatment for the achievement of local control of small and moderately sized EAD tumors, but it is likely of limited use in patients with larger tumors that have untreatable regions due to involvement of vital structures. Continued research evaluating cryoablation for the treatment of EAD tumors is needed.

Fibromatosis in a Young Bernese Mountain Dog: Clinical, Imaging, and Histopathological Findings

A young, intact, male Bernese Mountain Dog was presented to the animal hospital for lameness and diffuse thickening of the soft tissue in the right hind limb. Magnetic resonance imaging revealed multiple, multilobular, space-occupying lesions within and between the muscles of the right femur. Biopsies taken from the lesions revealed an infiltrative mass composed mainly of collagen fibers and a low density of benign-appearing fibroblasts. These findings were compatible with a diagnosis of a fibromatosis. Taking the age of onset into account, infantile fibromatosis was most likely. A deep fibromatosis, similar to that seen in adults, could not be excluded based on histology.