EP319 - I'm Floored! A Rare Pelvic Mass in a Young Female

Purpose/Background: Aggressive angiomyxoma (AA) is a rare, female-predominant mesenchymal tumor. It was first described in a 1983 case series of large, locally infiltrative pelvic tumors with microscopic pathology showing stellate and spindle cells separated by collagen-rich myxoid stroma with abundant vascular supply. It is often found incidentally, but significant tumor growth can induce abdominopelvic mass effect symptoms. MRI is the preferred imaging modality to assess for local invasion, and diagnosis is determined by histopathological analysis with myofibroblastic tumor markers. The mainstay of treatment involves surgical resection with negative margins. Alternative or adjunct therapeutic modalities include gonadotropin-releasing hormone (GnRH) agonists, radiotherapy and embolization. AA has high local recurrence rates, but distant metastasis is rare.

Methods/Interventions: Our case presents a 43-year old female who first noted a painless perianal nodule in 2020. CT imaging noted a 6.5 x 4.4 x 8.7 cm peri-anorectal mass without aggressive features, which was worked up with multiple non-diagnostic trans-rectal and percutaneous biopsies over a four year span. She continued to have progressive abdominal cramping and constipation, and initially presented to our institution in 03/2024 for an acute exacerbation of symptoms. Repeat CT imaging showed a circumscribed 9.4 x 4.8 x 20 cm hypodense mass in the presacral space with lateral displacement of the rectum. MRI imaging confirmed violation of the mesorectal fascia with extension through the right levator ani muscles into the ischiorectal fossa. Repeat endoscopic biopsy was non-diagnostic due to “scant cellularity”, and image-guided percutaneous biopsy yielded similar results. Given progressive enlargement and ongoing diagnostic uncertainty, excision was recommended. After appropriate preoperative counseling, she underwent open excision in which a gelatinous, rubbery mass was found enveloped within the right mesorectum extending through the levators into the ischiorectal fat. It was mobilized and separated off the lateral wall of the rectum to the anorectal junction inferiorly. Flexible sigmoidoscopy confirmed no leak after completion of the dissection.

Results/Outcomes: Our patient recovered from surgery uneventfully and was discharged to home. Final pathology revealed aggressive angiomyxoma with greatest dimensions of 31.7 x 16.2 x 4.9 cm. She was recovering well at outpatient follow-up and recommended surveillance with MRI pelvis in one year.

Conclusion/Discussion: This case highlights important considerations for management of AA. First, diagnosis can be difficult to obtain via percutaneous or endoscopic means given the myxomatous nature of these tumors. Patients often present with significant local disease burden, increasing the morbidity of excision for diagnostic and therapeutic purposes. Thorough preoperative imaging and counseling is critical to prepare patients for all possible outcomes. While we achieved resection without significant morbidity, neoadjuvant angioembolization may be considered if upfront resection is expected to be unacceptably morbid. Despite high risk of local recurrence, there are no definitive guidelines on surveillance. Our practice recommended serial imaging with MRI, though other cases have utilized GnRH agonists to facilitate tumor suppression.

Aggressive Angiomyxoma, Gross Specimen
Upper image: cut specimen showing tan, gelatinous, homogenous tissue.
Lower image: external view with left side showing portion of mass that extended into ischiorectal fossa.

Aggressive Angiomyxoma, MRI T1 Coronal Sequences
Left image: Coronal cut of mass abutting right rectal wall and extending past the anorectal junction (red arrowhead). Asterix shows rectum.
Right image: Coronal cut of mass extending through right levator ani (red arrow).