Aggressive gluteal fibromatosis: Rare case associated with spontaneous superior gluteal artery pseudoaneurysm

Deep fibromatosis is a locally aggressive neoplasm commonly involving the extremities.

Hassan Alsayegh et al report a case of a spontaneous development of pseudoaneurysm caused by deep fibromatosis, which could be a life-threatening condition and should be considered when dealing with deep fibromatosis and deciding on the appropriate treatment.

Deep fibromatosis (DF) is also known as musculoaponeurotic fibromatosis, desmoid fibromatosis, aggressive fibromatosis, and desmoid tumor, and the clonal proliferation of spindle cells has a high potential for local recurrence. Although these tumors do not metastasize, the clinical behavior of DF is unpredictable, varying from indolent to aggressive, making their treatment challenging.

A 33-year-old man, known to have a right lower ureteric stricture, presented with urinary retention, for which he underwent a diagnostic imaging workup. Computed tomography (CT) incidentally revealed a soft tissue mass in the right gluteal region with intrapelvic extension. Magnetic resonance imaging (MRI) was performed for further characterization of the gluteal lesion, which revealed a large, soft tissue intramuscular mass in the right gluteal muscles, measuring approximately 13×12.5×8 cm. The mass was abutting the sciatic nerve and near the superior gluteal artery without definitive invasion. The mass demonstrated heterogeneous isointense signal intensity on T1 and hyperintense signal intensity on T2, with internal strands of fibrous tissue manifested by low signal intensity on T2 and significant heterogeneous enhancement post-intravenous injection of gadolinium. The mass was abutting the sciatic nerve in the greater sciatic notch. The impression was aggressive soft tissue mass with differential diagnosis including DF and soft tissue sarcoma.

After taking more history from the patient, he admitted noticing the swelling in the right gluteal region at the age of 23 and did not undergo a workup. He had numbness and pain in the right leg for the last 1.5 years. Clinical examination showed a large right gluteal region mass in the upper outer quadrant. He underwent a core needle biopsy revealed low-grade spindle cell lesions with fibro-/ myofibroblastic features consistent with DF.

After a multidisciplinary team discussion, the decision was to follow up the mass by MRI every 6 months. On the initial follow-up, the patient was asymptomatic and showed a stable mass on MRI. On subsequent follow-up, the MRI showed an interval increase in the lesion size and follow-up continued. Approximately after 4 years of follow-up, MRI revealed an increase in the size of the mass in the form of a hematoma with pseudoaneurysm formation, which was likely from the right superior gluteal artery.

After approximately 2 weeks, the patient presented to the emergency department with a progressive increase in the size of the right gluteal mass and developed progressive severe right knee and foot pain uncontrolled by analgesics. On clinical examination, right leg movement show good power and sensation; however, there was a foot drop. CT angiography of the lower limbs demonstrated that the mass with the pseudoaneurysm likely originated from the right gluteal artery, which appeared to be smaller than the prior MRI finding with partial thrombosis. The patient’s symptoms improved after receiving opioids intravenously. No endovascular intervention was indicated, and the patient agreed to start urgent radiotherapy treatment.

The patient was kept under observation for 7 days, with interval stability of the clinical symptoms and vital signs. He was discharged to continue radiotherapy on an outpatient basis with weekly follow-ups in the radiation oncology clinic. Five sessions of radiotherapy were completed. On follow-up MRI obtained 3 months after the radiotherapy, the size of the mass reduced with thrombosis of the pseudoaneurysm. The orthopedic surgery department advised that no surgical intervention was required, and the patient was kept on clinical and radiological follow-up. The last MRI revealed further regression in the size of the right gluteal mass, with the resolution of the pseudoaneurysm and intralesional hematoma.

The authors commented - “We presented a rare case of right gluteal DF that showed spontaneous development of an intralesional pseudoaneurysm not related to prior surgical intervention or trauma with spontaneous development of partial thrombosis and regression on subsequent follow-ups. Such a spontaneous vascular pathology may necessitate a stricter follow-up and additional treatments including urgent radiation therapy and endovascular or surgical intervention.”

Further reading:

Aggressive gluteal fibromatosis: a rare case associated with spontaneous superior gluteal artery pseudoaneurysm

Hassan Alsayegh, Tariq Alzaid et al

Skeletal Radiology (2023) 52:1593–1598

https://doi.org/10.1007/s00256-022-04263-7