The tumor was resected. Histopathological examination showed loosely and haphazardly arranged spindle cells with bland, oval nuclei and minimal cytoplasm with interspersed collagen fibers. Admixed with these cells were also seen many plump spindle cells with moderate amount of eosinophilic cytoplasm tapering at ends and oval vesicular nuclei. At places, the tumor was invading and infiltrating the surrounding muscles resulting in degenerative changes of muscle fibers [Figure 1]. No necrosis or mitosis was seen. A histological diagnosis of extra-abdominal FM was made. Patient was on follow-up; and presented again after two months with gradually increasing swelling near the scar mark. On further clinical examination, two more swellings were seen on the left foot; the larger swelling at the base of great toe measured 4 × 3 cm and the smaller on the dorsal surface measured 3 × 2 cm in size; both the swellings were firm and non-tender. Patient was referred for fine needle aspiration (FNA) which was performed from all the three lesions and showed similar morphology. The smears showed high cellularity comprising of dissociated and cohesive clusters of plump spindle to oval and polygonal cells. These cells were bland-appearing with oval to elongated nuclei and prominent nucleoli; most cells showed one to multiple cytoplasmic processes. Also seen were many collagen fragments of variable cellularity. A few inflammatory cells were also present. Atypical mitosis or necrosis in the background was absent. Immunocytochemistry (IC) for vimentin was performed and showed strong cytoplasmic positivity [Figure 2]. These cytological features were compared with the previous histopathlogy and found consistent with a diagnosis of recurrent synchronous multicentric AFM. On further clinical history, there were no gastrointestinal complaints, swellings at any other site or family history of cancer; thus, ruling out syndromic association.

Most of the cases occur between puberty and fourth decade with female predominance.[3] They are usually slow growing, locally aggressive and invade surrounding tissues. Two types of FM are known, superficial and deep subtypes. The superficial FM are small and slow growing whereas the deep ones are larger, rapidly proliferating with a tendency to recur after treatment, therefore, also referred to as “AFM.” Deep subtype preferentially involves musculature of the trunk and extremities.[2] Clinical differential diagnosis includes soft-tissue lesions, myositis ossificans, lymphomas and bone tumors in extremities which can be ruled out radiologically.[7] In our case, the patient had large intramuscular FM in the thigh which recurred two months after excision. In addition, there were two distinct nodules in foot which showed similar morphology as that of thigh lesion suggestive of its synchronous and multicentric nature.

Radiologically, AFM reveals an infiltrative growth pattern invading fascial planes but without central necrosis, even in the largest lesions. Bands of low signal intensity across all sequences and uniform moderate to avid enhancement after gadolinium administration also can be seen, this feature is considered characteristic but not specific for AFM.[7]

The tumor grossly varies from 5-20 cm in size and confines to the muscles and overlying aponeurosis or fascia. They are firm and cut with a gritty sensation; cross section reveals a glistening white, coarsely trabeculated surface resembling scar tissue.[2] Morphological differential diagnosis include fibrosarcoma, reactive fibroblastic proliferations, desmoplastic fibroma, myxoma and nodular fascitis.[3] Microscopically, FM is poorly circumscribed and infiltrates the surrounding tissue. The cells are spindle to fusiform with oval to elongated nuclei, one to multiple small nucleoli and are separated from one another by variable amount of, usually abundant collagen.[2] The cells lack atypia with rare mitosis; in contrast well differentiated fibrosarcoma shows atypical cytological features and significant number of mitoses normally more than one per high power field.

FNAC plays an important role in the diagnosis of benign soft tissue tumors.[8,9] However, its role in the diagnosis of FM is limited and non-diagnostic; although in a typical clinical setting with a history of previous surgery near or at the site of FNA and presence of bland spindle cells with fusiform nuclei and metachromatic matrix, the cytological diagnosis of FM can be safely rendered. In the present case, history of prior fibromatosis, comparison of cytology with previous histological material and positive IC for vimentin facilitated the diagnosis of FM thus ruling out the other differential diagnosis.[3] Cytological differential diagnosis includes all other benign spindle cell lesions as mentioned above for histopathology. Nodular fascitis usually show ganglion like cells with eccentric nuclei, spindle cells and myxoid matrix; nerve sheath tumors show spindle cells with wavy nuclei and fibrillary stroma; smooth muscle neoplasm show plump curved nuclei; and spindle cell carcinoma and melanoma show pleomorphism, mitosis and necrotic background. In cases of difficulty, a panel of IC (EMA, HMB 45, desmin, S100, vimentin) helps in the definitive diagnosis.

The clinical behavior is unpredictable. They may regress spontaneously; usually have high recurrence rates but no metastasis. The risk of recurrence for extra abdominal tumors is low (5-50%) and is high even after complete resection for intra-abdominal tumors (57-86%) with high complication rate and even death. Most recurrences are seen within three years and nearly all by six years. Local recurrences are higher in extra abdominal lesions in a younger age, extremities because of their locally aggressive behavior and more with foot and calf lesions.[3] The management and treatment includes multimodality approach and includes surgery, radiotherapy (RT), chemotherapy and other drugs. Treatment of choice is radical excisionwith wide margins of involved tissue, although because of the tumor extent and infiltrative pattern, complete excision is difficult to achieve resulting in frequent recurrences.[3] External beam RT has a role in both adjuvant and primary control of tumor. The currently recommended dose is 50-60 Gy. Cytotoxic drugs have been used in unresectable tumors, progressive or residual disease and rarely as neoadjuvant to facilitate wide surgical resection. Low dose combination of vinblastin, methotrexate, vincristine, actinomycin D, cyclophoshamide and doxarubicine/dacarbazine has been used in different clinical settings. Non steroidal anti-inflammatory drugs, singly or in combination with anti-estrogens have been used currently with variable response rates. Disease progression may occur many years after treatment and patient should be on constant follow-up.[10]