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Image of the Month—Diagnosis
Arch Surg. 2006;141:942.
Answer: Schwannoma
Operative resection was planned via laparoscopy, with an approach similar to that of a left adrenalectomy. Intraoperatively, a solid mass anterior and inferior to the left renal vein was identified; it appeared encapsulated and was easily dissected free from adjacent structures (Figure 2). Her postoperative course was uneventful and she was discharged home on hospital day 2. Pathologic examination demonstrated a 5.4 x 4.3 x 3.7-cm mass with a well-developed capsule. Tumor cells stained positive for S100 protein and CD34 cells and negative for desmin and muscle-specific actin, which is consistent with a benign schwannoma.
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Figure 2. A laparoscopic approach was used to dissect the inferior and lateral aspects of the well-encapsulated, solid mass well away from the renal blood vessels and ureter before rotating the entire mass out of the bed of dissection.
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The majority of schwannomas occur in the head, neck, or extremities, with few cases reported originating in the retroperitoneum.1 Because patients may be asymptomatic or only have vague abdominal pain, these schwannomas may be identified incidentally when evaluating other patient complaints or they may grow to large sizes prior to overt symptoms. Schwannomas are associated with von Recklinghausen disease in 5% to 18% of cases, and patients generally present between the ages of 20 and 50 years, with only 5% having onset in childhood or adolescence.2 In the absence of von Recklinghausen disease, schwannomas rarely develop in the retroperitoneum, with only 3% of all sporadic schwannomas, both malignant and benign, occurring here.3 When sporadic, they are typically benign lesions, particularly when identified in the retroperitoneum.
On gross appearance and diagnostic imaging, they are solitary, well-circumscribed masses that do not invade local tissues.4 One can attempt to distinguish primary retroperitoneal benign tumors from their malignant counterparts using reported tumor scoring systems.5 Tumor size larger than 5.5 cm, presence of symptoms, absence of calcifications, presence of irregular margins, and the presence of cystic degeneration or necrosis may be valuable predictors of a primary retroperitoneal malignant tumor. Although computed tomography may be used to develop a differential diagnosis of neurogenic tumors and determine the local extension, malignancy cannot accurately be determined preoperatively.6 Computed tomography–guided biopsy may be unreliable because of cellular pleomorphism in areas of degeneration; hence, degenerative cells may be misinterpreted as malignancy.7
Because malignancy cannot be excluded preoperatively or even intraoperatively with frozen section analysis, complete surgical resection with partial or complete resection of adjacent viscera so as to attain negative margins is recommended.8 Additionally, although rare, malignant schwannomas act like high-grade sarcomas with a high incidence of local recurrence and distant metastasis4; therefore, definitive resection for diagnosis is mandatory on suspicion of such tumors. On pathologic examination, the presence of a well-developed capsule differentiates schwannomas from the more common neurofibromas. The histologic hallmark of benign schwannomas is a pattern of alternating Antoni A and B areas, with intense staining for S100 protein.4
Fewer than 10 cases of laparoscopic resection of a retroperitoneal schwannoma have been reported in the world's literature to date. Because of the retroperitoneal schwannoma's encapsulation, a laparoscopic surgical technique is feasible. Recognition and early surgical management of retroperitoneal benign tumors, such as a schwannoma, are encouraged for appropriate diagnosis and exclusion of malignant subtypes.
AUTHOR INFORMATION
Correspondence: C. Clay Cothren, MD, Department of Surgery, Denver Health Medical Center, 777 Bannock St, MC 0206, Denver, CO 80204 (clay.cothren{at}dhha.org).
Accepted for Publication: August 11, 2005.
REFERENCES
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1. Funamizu N, Sasaki A, Matsumoto T, et al. Laparoscopic resection of a retroperitoneal schwannoma behind the lesser omental sac. Surg Laparosc Endosc Percutan Tech. 2004;14:175-177.
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2. Antinheimo J, Sankila R, Carpen O, et al. Population-based analysis of sporadic and type 2 neurofibromatosis-associated meningiomas and schwannomas. Neurology. 2000;54:71-76.
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3. Gubbay AD, Moschilla G, Gray BN, Thompson I. Retroperitoneal schwannoma: a case series and review. Aust N Z J Surg. 1995;65:197-200.
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4. Enzinger FM, Weiss SW. Malignant tumors of peripheral nerves. In: Soft Tissue Tumors. 3rd ed. St Louis, Mo: Mosby; 1995:821-832.5. Nakashima J, Ueno M, Nakamura K, et al. Differential diagnosis of primary benign and malignant retroperitoneal tumors. Int J Urol. 1997;4:441-446.
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6. Rha SE, Byun JY, Jung SE, Chun HJ, Lee HG, Lee JM. Neurogenic tumors in the abdomen: tumor types and imaging characteristics. Radiographics. 2003;23:29-43.
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7. Daneshmand S, Youssefzadeh D, Chamie K, et al. Benign retroperitoneal schwannoma: a case series and review of the literature. Urology. 2003;62:993-997.
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8. Giglio M, Giasotto V, Medica M, et al. Retroperitoneal ancient schwannoma: case report and analysis of clinico-radiological findings. Ann Urol (Paris). 2002;36:104-106.
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SECTION EDITOR: GRACE S. ROZYCKI, MD
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