Residency Program - Case of the Month

Answer:

Angiomyofibroblastoma

Histologic description:

The tumor is composed of hypo- and hypercellular areas of spindle to oval shaped tumor cells.  Thick bundles of collagen are present between the tumor cells.  Small vessels with thin walls and some perivascular cuffing by the tumor cells are present.  The classic edematous stroma is not seen.

Discussion:

Angiomyofibroblastoma presents as a painless vulvar mass in women of reproductive and postmenopausal age. Often they are thought to be a Bartholin’s cyst by the clinician. Angiomyofibroblastoma is well circumscribed; the tumor in this case was subsequently resected and a gross photo is shown below.

Angiomyofibroblastoma is composed of alternating hypercellular and hypocellular edematous zones.  Numerous thin-walled small vessels are present.  The tumor cells can be spindled, oval, plasmacytoid, or epithelioid with eosinophilic cytoplasm and typically contain bland nuclei.  Occasionally, enlarged and hyperchromatic nuclei as well as multinucleated tumor cells can be seen, but mitoses are rare or absent.  There is condensation of the tumor cells around blood vessels.  Collagen is present in wavy strands or thick bundles throughout the tumor.  Adipose tissue can be present in the tumor (though not always).  Scattered lymphocytes and mast cells are commonly found within the tumor.

Immunohistochemical stains of the tumor include positive vimentin and desmin.  Estrogen and progesterone are usually positive.  Actin and CD34 are occasionally positive.  S100 is negative.

Local excision of the tumor is curative.

The differential diagnosis for angiomyofibroblastoma includes aggressive angiomyxoma and cellular angiofibroma.  Unlike angiomyofibroblastoma, aggressive angiomyxoma is often poorly circumscribed.  It is sparsely cellular.  The tumor cells are oval, spindle, or stellate in shape and are contained in a myxoid stroma with delicate collagen fibers.  Like angiomyofibroblastoma, numerous blood vessels are present; however, the vessels vary in size and have thin to thick walls.  Thick walled vessels are not present in angiomyofibroblastoma.  Immunohistochemistry of aggressive angiomyxoma is similar to angiomyofibroblastoma and does not help to delineate between the two.  In summary, angiomyofibroblastoma has areas that are more cellular than aggressive angiomyxoma, has blood vessels that lack thickened walls but often have perivascular condensation by the tumor cells.  And angiomyofibroblastoma can have more epithelioid tumor cells.  Aggressive angiomyxoma often recurs locally after excision, so the distinction is clinically relevant.

Cellular angiofibroma is a well circumscribed tumor like angiomyofibroblastoma.  The tumor is composed of a cellular proliferation of spindle cells with numerous small to medium thick walled, hyalinized blood vessels.  The spindle cells are bland and mitoses are uncommon.  Unlike angiomyofibroblastoma, cellular angiofibroma is usually negative for desmin and often positive for CD34.  In contrast to cellular angiofibroma, angiomyofibroblastoma will have more variable cellularity, perivascular condensation, and thin walled vessels.  It can also have populations of epithelioid or plasmacytoid tumor cells..  

References:

1. Clement PB, Young RH, Atlas of Gynecologic Surgical Pathology, Saunders Elsevier, 2008, pages 20-23.
2. Crum CP, Lee KR, Diagnostic Gynecologic and Obstetric Pathology, Elsevier Saunders, 2006, pages 182-184..