Aggressive Angiomyxoma of the Bladder Neck Requiring Local Excision and Mitrofanoff Formation

Aggressive angiomyxoma is a rare mesenchymal tumour predominantly affecting the female pelvis and perineum but has also been described in males. This tumour can often present a diagnostic challenge and has a propensity for local recurrence after surgical excision. We present an unusual case of aggressive angiomyxoma arising from the bladder of a female patient which required local excision and Mitrofanoff formation.


Description of Case
A 48-year-old lady presented with visible haematuria and UTI. Pelvic examination revealed a mobile pelvic mass attached to the bladder neck. MRI revealed an 85 × 40 mm mass arising from the bladder neck. The tumour appeared hypointense on T1-sequence and had a swirled, heterogeneous appearance on contrast enhanced T2-sequences ( Figure 1). Differential diagnoses included urethral diverticulum or leiomyoma.
The patient presented subsequently with acute kidney injury requiring bilateral percutaneous nephrostomy insertion. Examination under anaesthesia and cystoscopy with loop resection biopsies were performed. Histological analysis demonstrated fibromuscular tissue with moderately cellular lesions consisting of short spindle cells with intervening thick-walled ectatic blood vessels. There was focal evidence of myogenic differentiation but no significant cytological atypia, nor mitotic activity or necrosis. The proliferation fraction with MIB1 was 1%. The working diagnosis was low grade muscle sarcoma.
Surgical resection of the mass was undertaken via Pfannenstiel and vaginal approaches to gain access to the point of attachment of the mass in the left paraurethral area.
Ultimately a urethrectomy was required, with concomitant bladder neck closure, Martius fat pad interposition, and creation of a catheterisable Mitrofanoff channel from the appendix. Nephrostomies were left in situ. Intraoperatively bilateral JJ stents were placed to protect the ureteric orifices during bladder neck closure.
The patient was discharged from hospital on day 15. At week three during fluoroscopic right nephrostomy removal, the distal J of the stent retracted into the distal ureter, and calcification of the left tube prevented its removal (Figure 2). At 12 weeks of bilateral PCNL, removal of left nephrostomy and both JJ stents was undertaken.
The mass measured 140 × 170 × 70 mm, with histopathological features of aggressive angiomyxoma (AAM) with spindle and epithelioid cells on fibrous stroma with a myxoid area (Figure 3). Although the mass was completely excised, the potential for local recurrence was noted and surveillance with periodic MRI scans of the pelvis is planned.

Discussion
AAM is a rare mesenchymal neoplastic tumour-the term "aggressive" was used to denote its propensity for local  recurrence [1]. These neoplasms primarily arise in the pelvic and perineal region of adult females but have been described in males [2]. AAM can present a diagnostic challenge with nonspecific symptoms, leading to misdiagnosis with more common entities. AAM has a variable appearance on CT. On MRI, it is hypointense on T1-weighted images and hyperintense on T2-weighted images and demonstrates a characteristic swirling pattern with contrast enhancement, due to its myxoid nature [3].
Surgical excision remains the first-line treatment, although positive resection margins occur due to soft tissue infiltration and absence of a capsule [4]. However, positive surgical margins may not be prognostic: a review of 111 cases demonstrated no significant difference in time to recurrence with margin status [2]. Recurrence rates range 25-47%, usually within 5 years, and cases of metastasis have been reported; hence radiological follow-up is advocated [2,5]. Though rare, clinical suspicion is required in order to not miss this diagnosis, and multidisciplinary care is key to obtaining a good outcome.