Atypical Presentation of a Retrorectal Ancient Schwannoma: A Case Report and Review of the Literature

Military Medicine, Aug 2008 by Santiago, Camilo, Lucha, Paul A

ABSTRACT Retrorectal tumors are rare and frequently present either incidentally or with vague symptoms. Schwannomas of the presacral region are one variant described as benign tumors of neurogenic origin. The "ancient degenerative variant" is uncommonly reported. We present the case of a 37-year-old man presenting with symptoms of left renal colic, impotence, and left trochanteric pain. Computed tomography and magnetic resonance imaging of the pelvis showed a presacral mass with cystic changes and calcifications consistent with a schwannoma. The patient underwent an exploratory laparotomy with resection of the tumor, which subsequent analysis showed to be a schwannoma with ancient degenerative changes.

INTRODUCTION

Retrorectal tumors present infrequently and comprise a variety of pathologic entities mat originate from the various tissue types present in the presacral space. These tumors represent ~1 in every 40,000 hospital admissions. In retrospective reviews, 50 to 57% were pathologically benign and 26% were asymptomatic.1,2 Presacral schwannoma is one of the described pathologic entities representing ~1 in 250 of all retrorectal tumors and is frequently present as a solitary mass.3 The most common presentation is as an incidental finding on routine rectal or pelvic examination; however, they may present with a variety of symptoms ranging from chronic pelvic and back pain, impotence, lower extremity pain and numbness, urinary incontinence and/or retention, and, rarely, renal colic symptoms. If the neurologist is asked to work up a radiculopathy, he or she might shift attention postelectromyelogram to proximal nerve roots and may choose a myelogram as the imagery of choice. Consideration should be addressed toward the abdominal cavity and a computed tomography (CT) or magnetic resonance imaging (MRI) addressing the abdomen and spinal chord should be entertained. This wide range of symptoms makes it difficult to suspect a retrorectal tumor based on clinical history and physical alone.4 Most patients do not experience symptoms until the mass has grown to a significant size; some experts estimate that symptoms may not occur for 7 years or more.5,6

Most schwannomas (85%) present as masses off midline arising along the course of any myelinated nerve and coursing into one of the sacral foramina; they are frequently palpable on rectal or pelvic examination.7 The patient should undergo a complete blood count, fecal occult blood examination, and a urinalysis with microscopic evaluation, to screen for the possibility of a gastrointestinal malignancy, a potential urologic malignancy or pathology, or gynecologic malignancy or pathology. Biopsy, transrectal or otherwise, is to be avoided to prevent sepsis, meningitis, abscess, or tumor seeding.1,2 Often mese laboratory studies are normal or inconclusive and imaging using CT or MRI is advised. The most common imaging study obtained is a CT scan, which often is unable to discern between malignant and benign presacral schwannoma. MRI can more frequently determine malignant vs. benign schwannoma.8,9 Most authors advocate performing MRI of the mass to try and better delineate the nerve roots involved.10-12

CASE REPORT

A 37-year-old man presented to the Emergency Department complaining of left flank pain, urinary hesitancy, and frequency wim associated dysuria. On further questioning, there was a history of left "hip" pain and impotence of unclear etiology. He had a previous medical history significant for urolithiasis. His laboratory evaluation was significant for a normal complete blood count and a normal urinalysis. CT for urolithiasis was obtained. This revealed no evidence of renal lithiasis and a 5.8- � 3-cm left-sided presacral mass at the level of S2 which had an enhancing capsule and distinct tissue planes. Further evaluation with a formal abdominal and pelvic CT scan and an MRI with contrast of the pelvic area demonstrated the presence of cystic and calcified areas within the mass (Figs. 1-3). There was no evidence of invasion to adjacent tissues. Based on this evaluation, the patient was taken to the operating room where a laparotomy was performed and the mass was resected en bloc. The mass was sent for frozen section which was inconclusive. Final histopathologic evaluation revealed an ancient degenerative benign schwannoma with cystic and associated calcific changes. At 1-year postoperation, he remains disease free with no neurological sequella.

CONCLUSION

An ancient schwannoma has a characteristic appearance on CT and MRI scanning consisting of encapsulated solid components with cystic areas, or appearing as cystic masses with marginal crescent-shaped or nodular solid components often containing calcifications.13,14 The ancient degenerative variant of presacral schwannoma often show stromal and vascular degenerative changes including cystic formation, central tissue loss, nuclear atypia, and calcification.15 These pathologic findings may be confused with sarcoma. This is the second report describing the clinical presentation of presacral schwannoma as possible renal colic.3 The treatment of all presacral schwannomas include en bloc resection of the mass, either via a transabdominal approach, a posterior sacral approach, or a combined procedure, entirely dependent on the sacral level at presentation. Retrorectal tumors, including presacral schwannoma, can be a diagnostic challenge due to the wide range of symptoms that may be present. Once the diagnosis is established, resection may provide marked improvement in patient symptoms if present. Resection is the recommended approach to establish the histological diagnosis.