Angiomyofibroblastoma C.D.M. Fletcher (In Soft tissue...WHO Blue Book)

Definition
A benign, well-circumscribed myofibroblastic neoplasm, usually arising in the pelviperineal region, especially the vulva, and apparently composed of stromale cells distinctive to this anatomic region. There may be morphologic overlap with cellular angiofibroma.

Epidemiology
Angiomyofibroblastoma is uncommon, having an incidence comparable to aggressive angiomyxoma. These tumours arise predominantly in females, principally in adults between menarche and menopause. Around 10% of patients are postmenopausal. Convincing examples have not been described before puberty. Rare cases occur in males.

Sites of involvement
Virtually all cases arise in pelviperineal subcutaneous tissue, with the majority arising in the vulva. Around 10-15% of
cases are located in the vagina. Lesions in men occur in the scrotum or paratesticular soft tissue.

Clinical features
Most cases present as a slowly enlarging, painless, circumscribed mass. The most frequent preoperative diagnosis is
Bartholin’s gland ‘cyst’. The aetiology is unknown.

Macroscopy
These lesions are well circumscribed but not encapsulated, with a tan/pink cut surface and a soft consistency.  Necrosis is not seen. Most cases measure less than 5 cm in maximum diameter, although rare examples measuring up to 10 cm have been recognized.

Histopathology
Tumours are generally well demarcated by a thin fibrous pseudocapsule and, at low power, show varying cellularity with prominent vessels throughout. Vessels are mostly small, thin-walled and ecstatic and are set in an abundant loose, oedematous stroma. The tumour cells are round-to-spindle shaped with eosinophilic cytoplasm and typically are concentrated around vessels. Mitoses are rare. Binucleate and multinucleate tumour cells are common. Some cases show very plasmacytoid or epithelioid cytomorphology and rare examples show degenerative (‘ancient’) nuclear hyperchromasia and atypia. Around 10% of cases have a variably prominent well differentiated adipocytic component. In post-menopausal patients the stroma is often less oedematous and more fibrous and there may be hyalinization of vessel walls. Some cases show morphologic overlap with cellular angiofibroma and rare cases show morphologic overlap with aggressive angiomyxoma.

Immunohistochemistry
The majority of cases show strong and diffuse desmin positivity, while, at most, there is usually only focal positivity for smooth muscle actin or pan-muscle actin. Desmin staining may be reduced or absent in postmenopausal cases. Tumour cells are consistently positive for oestrogen receptor and progesterone receptor, occasionally positive for CD34 and negative for S100 protein, keratin and fast myosin.

Ultrastructure
Tumour cells show fibroblastic or myofibroblastic features by electron microscopy.

Prognostic factors
Angiomyofibroblastoma is entirely benign and has never been reported to recur locally, even after marginal local
excision. There is one reported case of a clinically malignant counterpart of angiomyofibroblastoma.

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Am J Surg Pathol. 1998 Jan;22(1):6-16

Angiomyofibroblastomalike tumor of the male genital tract: analysis of 11 cases with comparison to female angiomyofibroblastoma and spindle cell lipoma

Laskin WB, Fetsch JF, Mostofi FK.
Department of Pathology, Northwestern University Medical School, Chicago, Illinois 60611-3053, USA.
The clinicopathologic features and immunoprofile of 11 cases of an uncharacterized male genital tract tumor with features of vulvovaginal angiomyofibroblastoma (AMF) and spindle cell lipoma (male AMF-like tumor) are described. The lesions presented as a mass involving the scrotum (six cases) or inguinal region (five cases) in males ranging in age from 39 to 88 years (median 57). The tumors were superficially located and well-marginated and ranged in size from 2.5 to 14 cm (approximate mean 7 cm). Microscopically, they were composed of tapered spindled cells proliferating between numerous small to medium-sized vessels. Epithelioid appearing stromal cells were a focal finding in four cases. Mitotic activity was minimal with no abnormal mitotic figures identified. Mild nuclear atypia was identified in two cases. The tumors possessed an acid mucopolysaccharide-rich, finely collagenous stroma. A small quantity of intralesional fat was present in six cases. Tumor cells exhibited immunoreactivity for vimentin (seven of seven cases), progesterone receptor protein (five of seven cases), CD34 (four of eight cases), estrogen receptor protein (three of seven cases), desmin (three of eight cases), muscle-specific actin (three of eight cases), and smooth-muscle actin (two of eight cases) but not for S-100 protein. One of seven patients with follow-up after simple excision had recurrent/persistent disease. The male AMF-like tumor is a soft-tissue neoplasm of the male genital tract that shares clinicopathologic features and a proposed perivascular stem cell derivation with both the female angiomyofibroblastoma and spindle cell lipoma.