Aggressive Angiomyxoma: An Unusual Scrotal Mass

Scrotal masses are a frequent complaint in general practice. A benign from a malignant scrotal lump had to be distinguished by the treating doctor in order to perform the precise surgery and provide ongoing care.

A 61-year-old male presented with a painless scrotal mass for six months duration. On clinical examination, the scrotal mass was firm and fixed to the perineal membrane (Table/Fig 1)a. Magnetic Resonance Imaging (MRI) scan revealed a 13X8X5 cm heterogeneous soft tissue mass (Table/Fig 1)b in the peranal/ perineum lesion abutting anterior wall of anal canal, root of penis and scrotum, the possibility of myxoid/spindle cell neoplasm of perineum to be considered was mentioned; in addition, remark of locally aggressive neoplasm, likely of malignancy was made in view of presence of infiltrating margins. Trucut biopsy was reported as a benign soft tissue tumour. Trans-scrotal excision was done. The postoperative resected specimen was sent for histopathological examination (Table/Fig 1)c.

Gross appearance of the external surface was grey white to grey brown. Cut surface was homogenous grey white soft in consistency with solid region at one pole measuring 7×5×0.5 cm [Table/Fig- 1]d. No areas of necrosis or haemorrhage noted. Tissue bits from representative sites were given. The microscopic examination revealed an unencapsulated infiltrative hypocellular lesion composed of spindle to stellate shaped tumour cells with delicate cytoplasmic processes and bland nuclear chromatin. No atypia or increase in mitosis was noted. The tumour cells were seen to be embedded in a myxoid stroma with scattered delicate collagen fibers (Table/Fig 2)a.

Entrapment of mature adipose tissue was noted at foci [Table/Fig- 2]b. Numerous small and medium sized thick walled hyalinised blood vessels were also noted and it was reported as Aggressive Angiomyxoma (AAM). The patient did not have recurrence at three and six month postoperative follow-up period.

Scrotal masses accounts to 1% of cases in the surgical Out Patient Department (OPD). Although some types of scrotal masses are more prevalent at particular ages, they can appear at any age (1). AAM is a very rare benign spindle cell mesenchymal tumour usually occurring in the pelviperineal region, more commonly in females than males (M:F is 1:7) in their fourth decade (2). It was first described in 1983, by Steeper and Rosai. So far only 36 cases of scrotal AAM are reported in the literature. AAM usually present as a painless mass. About 30% of these tumours recur locally, as it shows infiltrative nature hence the term ‘Aggressive’, although distant metastasis is extremely uncommon, MRI aids in determining the tumour’s extent (3).

Its aetiology is not clearly established yet. Few studies hypothesised that AAM might develop from stem cells with the capacity for multiple differentiation near arteries that eventually give rise to fibroblasts and myofibroblasts (4),(5).

Most AAM patients noted to have a long history of asymptomatic mass or swelling in the scrotum. The tumour size range from 1.5 cm to as big as 25 cm. The genital location and subtle clinical presentation of the tumour delays the treatment requirement by patients, which leads to a progressively growing tumour size with a high rate of clinical misdiagnosis. It is challenging to get an accurate preoperative diagnosis, and the differential diagnosis includes non neoplastic and neoplastic lesions (5).

On macroscopic examination, AAM is typically a soft, lobulated, grayish-white, fairly delineated tumour with vague infiltrative margins and myxoid appearance. The essential diagnostic criteria of AAM include the histological features of ill marginated lesion with uniformly dispersed tumour cells in abundant myxoid stroma, vascular components and invasive proliferation. The bland tumour cells may be spindled, star or oval-shaped with bland nuclei and sparse mitoses. The vessels may vary from thick hyalinised or thin-walled walls of different diameters. The aberrant HMGA2 expression is considered as desirable for diagnosis however is not essential, as its sensitive but not specific marker for AAM. It is useful especially to define tumour margin, as the non tumourous mesenchyme lacks positivity to HMGA2 (6).

AAM in the scrotum is typically treated with a large local excision with tumour-free surgical margins (7). When surgical complications are common or fertility retention becomes an issue, some specialists think incomplete or partial resection is permissible. The likelihood of local AAM recurrence is significant and differs by gender, particularly within 2-3 years.

Myxoid liposarcoma, angiomyofibroblastoma, myxoid neurofibroma, and myxoma are the tumours in the main differential diagnosis of AAM. Malignant myxoid neoplasms should be recognised from AAM since the management protocol varies for the both. Although it is not usually necessary, immunohistochemistry aids in distinguishing AAM from other mesenchymal tumours. Desmin, Vimentin, Smooth Muscle Actin (SMA), and CD34 are all positive in AAM, while S-100, CK, and CD68 are all negative (6).

Due to its infiltrative boundaries, AAM might radiographically evoke suspicion of malignancy, as in the present case. Owing to the rarity of this lesion and lack of distinct imaging findings, an accurate preoperative diagnosis is frequently challenging. From the experience with above described case and literature reviews, it was observed that the preoperative imaging techniques and intraoperative pathology investigations can partly aid with the diagnosis. However, the gold standard for the diagnosis of AAM relies on the thorough histological evaluation of postoperative specimens. Despite being an uncommon phenomenon in the male genital region, the surgeon should consider it as one of their differential diagnosis to prevent over diagnosing malignancy and subsequent treatment.