Teaching Case

A 49-year-old female patient came to the hospital for a screening mammogram. There was no history of any lump, breast pain or nipple discharge. On examination, no significant palpable abnormality was noticed.

Mammogram was performed which revealed focal area of architectural distortion in the upper outer quadrant of the left breast. Correlated ultrasound revealed small echo-poor area with associated distortion and spiculations which were reaching up to the overlying skin in the upper outer quadrant of the left breast with an overall area of abnormality measuring 25x10 mm.
MR mammography revealed altered signal intensity area appearing hypointense on T1, iso-hyperintense on T2 showing intense post-contrast enhancement. The spiculations were reaching up to the overlying skin with resultant skin dimpling. The lesion showed type III curve on further investigation. Ultrasound-guided core needle biopsy was performed which revealed spindle cell neoplasm, hence excision was suggested which revealed fibromatosis.

Spindle cell lesion of the breast is a very challenging diagnosis due to the various types, which all present differently on mammography, ultrasound and MRI. Types of spindle cell lesions are given below [1]:

BENIGN - PASH, haematoma, phylloides tumour, lymphocytic mastopathy, fibromatosis, nodular fasciitis, spindle cell lipoma, myofibroblastoma, mammary schwannoma, traumatic neuroma.
MALIGNANT - Metaplastic CA, angiosarcoma, malignant phylloides, MFH-malignant fibrous histiocytoma, spindle cell CA, solitary fibrous tumour/haemangiopericytoma.

Fibromatosis is also known as extra-abdominal desmoid tumour, which represents 4% of all extra-abdominal desmoid tumours. It is a soft tissue tumour composed of spindle cells and collagen. [2]
The aetiology remains unknown. This condition may occur sporadically but also has been noted after trauma/previous breast surgical procedure likely augmentation/implants. [2] It is associated with the Gardner syndrome, which includes familial adenopolyposis (FAP), multiple osteomas, epidermal cyst, fibromatosis, desmoid tumour of mesentery and anterior abdominal wall. Generally, these present as a painless palpable mass with or without skin dimpling/retraction. [1]
At mammography fibromatosis of the breast typically presents as a spiculated irregular non-calcified mass mimicking malignancy. [1] Ultrasound features include echo-poor mass with irregular borders and spiculations [1], making it difficult to differentiate from malignancy. It also has the appearance of well-circumscribed border, posterior acoustic enhancement and parallel orientation. [2] On MRI it appears as irregular ill-defined mass that is isointense on T1, variable intensity on T2-weighted images with variable kinetics. [2] Fibromatosis has the tendency of local invasion, hence MRI is the best imaging tool to know the exact extent of the disease and to see the involvement of the pectoralis muscle and skin. Imaging findings often mimic malignancy, hence core-needle biopsy is strongly recommended to exclude malignancy. [1]
Wide local excision with clear margins remains the treatment of choice for fibromatosis. [2] Recurrence rates are high and have been reported up to 29% especially in those which are involving pectoralis muscle and also in those with positive margins. [2] Radiation plays a role for patients with unresectable tumours or lesions that would require extensive surgical resection including amputation or major chest or abdominal wall resection. [2]
Mammary fibromatosis (extra-abdominal desmoid tumour) is considered a rare breast tumour, in particular a rare non-metastasising benign but locally invasive spindle cell neoplasm. Awareness of this lesion is important as it can mimic more sinister types of breast cancer on both imaging and clinically, leading to diagnostic dilemma.