A 65-year-old Caucasian female with a history of diverticulitis and atrophic vaginitis presented with a 2-week history of left-sided abdominal pain. The pain was in both upper and lower quadrants and seemed to be associated with deep inspiration. Review of systems was negative for fever and chills although she did complain of constipation. She denied any change in the color of her stool. Her only medication was topical vaginal estrogen.
Imaging was recommended owing to the concern for possible diverticulitis. A computed tomography scan of the abdomen and pelvis showed diverticulosis without diverticulitis. A 9 cm x 4 cm x 10 cm right-sided perirectal mass was seen extending from the right pubococcygeal muscle into the perirectal fat planes with no adjacent lymphadenopathy. The patient underwent a subsequent magnetic resonance imaging of the abdomen and pelvis which showed a complex right-sided perirectal mass extending from below the level of the levator ani into the right buttocks and towards the thigh (Figure 1).
Differential diagnosis included an abscess or a necrotic neoplasm. An initial transrectal biopsy was unsuccessful so she underwent surgical excision which revealed a well-encapsulated perirectal mass consistent with some type of smooth muscle tumor. The lesion was adherent to and extended through the levator plate; therefore, complete resection was not possible.
The pathologic evaluation showed the mass to be composed of cytologically bland spindle and stellate cells, with indistinct cell borders, present within fibromyxoid stroma. There was mild variation in cellularity and mitotic activity was inconspicuous. Throughout the lesion there were variably sized vessels of uneven wall thickness, some of which were surrounded by a thin fibrous cuff. An occasional vessel showed the presence of hyperplasia of the media.
Additionally, there were patchy areas of extravasated red blood cells. Perivascular epithelioid cells were not identified. The tumor extensively abutted and appeared transected at the margin. These findings were consistent with an incompletely resected aggressive angiomyxoma. Testing for estrogen- and progesterone-receptor status was positive.
Topical vaginal estrogen was stopped and tamoxifen therapy was started. Follow-up imaging at 12 months showed the patient to be in remission. Annual follow-up was recommended.
Aggressive angiomyxoma is a very rare soft tissue tumor (Hum Pathol 2003;34:1072-1074). It occurs almost exclusively in the genital and perineal area of female patients and most commonly occurs in the third to fifth decades of life (Cancer 1996;78:79-90). Despite the bland appearance and slow growth of this neoplasm, these lesions aggressively infiltrate the perivaginal and perirectal soft tissue and have a propensity to recur locally, hence the name aggressive angiomyxoma. The recurrence rate can be as high as 70 percent, and most of these relapse within the first 2 years but may recur as late as 20 years (Int J Gynecol Cancer 2004;14:94-99).
Complete excision is the preferred management when it can be accomplished without undue morbidity. This may not always be surgically feasible due to the proximity to perineal structures as demonstrated in this case. It has been established that this tumor may possess estrogen and/or progesterone receptors, suggesting that aggressive angiomyxoma is a hormonally responsive neoplasm (J Clin Pathol 2000;53:603-605). More recently, studies have shown dramatic response to hormonal therapy, especially in tumors that are receptor-positive, which may be a valuable therapeutic tool in the adjuvant setting for residual tumors (Int J Urol 2004;11:432-435). The optimal duration of hormonal therapy is not well-known. There have been rare cases of aggressive angiomyxoma demonstrating metastatic behavior (Hum Pathol 2003;34:1072-1074).
Patients with aggressive angiomyxomas will require long-term follow-up with periodic imaging analysis as the physical examination has a low sensitivity for detecting recurrence. Due to the slow nature of the tumor growth, recurrences may be late in onset as described above. Although the patient described in this case has done well at the 1-year mark, raising the possibility that the incompletely resected tumor has indeed responded to tamoxifen, long-term follow-up and further studies will be needed to confirm this notion.
ABDUL RISHI, MD, & SHAUN DONEGAN, MD, are from the Division of Hematology and Oncology in the Department of Internal Medicine at Mercy, St. Louis.
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