DISCUSSION:
AFH was initially described by Enzinger1 in 1979 as malignant angiomatoid fibrous histiocytoma. They constitute around 0.3% of all soft tissue tumors.2-5. However, the data may be understated because of the overlapping histopathological findings.5 But, The World Health Organization (WHO) in 2013 classification placed it in the category of “intermediate tumors of uncertain differentiation” because of its better prognosis2,4-13 .Although AFH can occur at any age but most patients present in the first three decades of life .In our case, the patient was in her forties. Although patients with AFH typically present with a painless subcutaneous soft tissue lump5,10 , Costa and Weiss3 reported that 18% of tumors invaded deep structures such as skeletal muscle. In our case, it was a painless swelling in the popliteal fossa region. Intraoperatively it was intraarticular in location and stump was found to be attached to the underlying bone. It most commonly arises in sites of normal lymphoid tissue such as the antecubital fossa, axilla, inguinal and supraclavicular regions 5,8,13.The majority of cases occur in the extremities, although cases have been reported in the head and neck region (10%) and trunk1,5,6,13. The cumulative findings of a meta-analysis of multiple studies demonstrate that the majority of patients (73.2%) are disease free after local excision and a minority (23.2%) develop recurrent disease and 8.7% metastasise within 24 months of surgery3. Metastasis occurs predominantly to regional lymph nodes but exceptionally to the lungs, liver, or brain.13
Making a pre-operative diagnosis of AFH is challenging with no distinct clinical or imaging findings to lead to diagnosis. There is a vast variability of the differential diagnoses which includes: Aneurysmal bone cysts, schwannoma, synovial sarcomas, aneurysmal fibrous histiocytomas, follicular dendritic metastatic tumor of lymph nodes .11,13 The presence of systemic symptoms, such as weight loss, malaise, fever, and anemia , which occur in some patients, can aid diagnosis5,6,10,11 The cause of these constitutional symptoms are thought to be due to the tumoral cytokine production5. However, in the current case, the patient experienced no systemic symptoms.
The imaging modalities are not diagnostic but aid in the management. The Computed tomography may show a heterogeneous mass and possibly hint at cystic and enhancing components. MRI is superior to CT scan for the diagnosis and explaining the relationship with the surrounding structures5 .Although the MRI features of AFH described in the literature may aid diagnosis , none of them are considered to be significant11 .MR has been traditionally used for postoperative follow-up. MRI was not done in our case due to non-availability in our institute and we proceeded with an excisional biopsy after the USG report.
Histopathological features of AFH have been well described2,11.This includes the following features:(i) multinodular growth of myoid spindle or histiocytoid cells with a distinctive syncytial appearance, (ii) pseudoangiomatous spaces filled with blood and surrounded by tumor cells, (iii) a thick fibrous pseudocapsule with prominent hemosiderin deposition, and (iv) peritumoral lymphoplasmacytic cuffing with occasional germinal centre formation. These features were consistent to our case. AFH lacks a specific immunoprofile, so that immunohistochemistry is supportive rather than diagnostic. Immunohistochemistry variably demonstrates positivity for desmin, CD68 and CD99 5,7,9-12 .Lastly, cytogenetic analysis has recently added to the diagnosis of AFH, with the EWSR1-CREB1 fusion gene present in the majority of AFH5,8-12
The prognosis of AFH is generally considered to be favorable2,9-12 but because of its chances of local recurrence ,soft tissue sarcomas should be operated by a specialised surgeon and special consideration should be taken not to miss these tumors preoperatively . There should be wide surgical excision with clear margins. Extended resection of AFH is recommended because the tumor is considered intermediate and not purely benign as it requires continued clinic radiological surveillance 5 .
There were some limitations in the current study. We did not perform immunohistochemistry for desmin and did not examine fusion genes, which are often useful for differential diagnosis. However, a diagnosis of AFH could be made in specimen Biopsy. Given the intermediate malignant potential of this lesion, the patient will require continued clinical and radiographic surveillance.