Case of the Week

2021-26/ June 28

Contributors: Ronald Cody Weimholt

A male in his 60s presented with a scrotal mass of 4 years duration but with increased growth in the last several months. MRI demonstrated a 13 cm well circumscribed mass with a dark T2 signal and T1 iso-intensity.

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Quiz

1. What is the correct diagnosis?

a. Diffuse type neurofibroma

b. Solitary fibrous tumor

c. Low grade fibromyxoid sarcoma

d. Cellular angiofibroma

e. Well differentiated liposarcoma/atypical lipomatous tumor, sclerosing subtype

The tumor was well circumscribed and composed of a sparsely cellular population of bland spindle cells within a homogenously collagenized background. Rarely the spindle cells were more atypical with pleomorphism and hyperchromasia. Scattered mast cells were present and evenly distributed throughout the tumor. There were numerous small to medium sized ectatic vessels within the tumor, some with thickened walls. There was no evidence of hypercellularity, mitotic activity, or necrosis. There was no evidence of lipoblasts or mature adipocytes. Immunohistochemical studies showed the tumor cells to be positive for SMA (patchy), desmin, CD34, ER and PR (scattered cells), while negative for MUC4, STAT6, S100 protein, EMA and AE1/AE3/PCK26. Rb expression was lost in tumor cells. These combined findings were diagnositic of a cellular angiofibroma.

Cellular angiofibroma is a rare benign fibroblastic neoplasm occuring in the vulvar or inguinoscrotal regions in women and men, respecively. The average age of incidence is in the fifth decade. These tumors are part of the spectrum of tumors known as the 13q/RB1 family of tumors which includes cellular angiofibroma, spindle cell/pleomorphic lipoma, and myofibroblastoma (mammary and soft tissue types). These all share a similar genetic pathogenesis characterized by partial or complete losses of chromosome 13.

These tumors are well circumscribed nodules that range in size from <1 cm to 25 cm. The tumor composition varies in cellularity and can show a background that is fibrous, hyalinized, myxoid, or edematous. Thick wall blood vessels and mast cells are characteristic. Degenerative nuclear atypia and small collections of mature adiopcytes can be seen. Rarely sarcomatoid change can occur, but those reported have not developed recurrence or metastasis.

Flucke U, van Krieken JH, Mentzel T. Cellular angiofibroma: analysis of 25 cases emphasizing its relationship to spindle cell lipoma and mammary-type myofibroblastoma. Mod Pathol. 2011 Jan;24(1):82-9.

Iwasa Y, Fletcher CDM, Flucke U. Cellular angiofibroma. In: WHO Classification of Tumours Editorial Board. Soft Tissue and Bone Tumours. Lyon (France): International Agency for Reasearch on Cancer; 2020 (WHO classification of tumours series, 5th ed.; vol.3): 80-81.

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