Extra-abdominal desmoid-type fibromatosis

Case contributed by Dr Eid Kakish

Presentation

Painless palpable right hip lump discovered incidentally on urinary tract CT scan for investigation of ureteric colic.

Patient Data

Age: 25 years
Gender: Female

Significant asymmetry is noted between outer aspects of the right and left proximal thighs.

An ill-defined lobulated mass is seen closely related to the right proximal iliotibial tract, abutting the adjacent gluteus medius and maximus with obliteration of the intervening fat planes. It appears slightly hypodense to the adjacent muscles, with multiple hyperattenuating intralesional streaks. The subjacent bony structures are intact.

There is a large oblong lobulated infiltrative soft tissue mass in the outer aspect of the proximal right thigh, predominantly centered in the proximal superficial fibers of the right iliotibial tract and invading the adjacent gluteal aponeurotic fascia and overlying superficial fascial layer. 

It demonstrates a predominantly isointense signal on T1WI, corresponding to a heterogenous high signal on T2WI and a hyperintense signal on PD with an intense heterogenous pattern of enhancement on T1 C+. Mild edema and contrast enhancement in the outer portions of the right gluteus medius muscle and intermuscular soft tissues. 

Multiple curvilinear intralesional bands are present, demonstarting a hypointense signal on all sequences with no appreciable contrast enhancement, strongly suggesting internal fibrous tissue.

Impression:

Aggressive fibrous tumor of the right proximal thigh, invading the adjacent iliotibial tract, gluteal aponeurotic and superficial fascia. 

There is a lobulated proximal right thigh mass with a low Standard Uptake Value (SUV) of less than 2.5, particularly in its periphery, centered in the right iliotibial band. 

Patient underwent surgical excision.

Histopathology: Right hip soft tissue mass positive for SMA and β-catenin.

Final diagnosis: Fibromatosis (Desmoid tumor), incomplete excision.

Case Discussion

Desmoid fibromatosis (DF) may be sporadic or familial in nature. Patients with familial adenomatous polyposis and Gardner syndrome are at an increased risk of developing desmoid tumors.

DF may be sporadic or familial in nature. Familial cases usually develop intra-abdominal or abdominal wall tumors, contrasted to the sporadic cases, which usually tend to develop aggressive extra-abdominal desmoids. 

The etiology is not well understood, believed to be related to various genetic or hormonal factors, as well as previous trauma and surgery.

Aggressive fibromatosis usually originates from muscular connective tissues, aponeurosis or fascia, such as in this case. 

They are benign locally aggressive tumors with no metastatic affinity. Given their infiltrative aggressive nature, incomplete surgical resection is a common problem, resulting in high local recurrence rates. 

FDG PET/CT does not particularly aid in differentiating malignant from benign soft tissue tumors. Desmoid tumors may show variable degrees of uptake.

 

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