Evaluation of perinephric, retroperitoneal schwannomas: case report and review of the Literature.

Abstract: Schwannomas are tumors arising from the nerve sheath. Because of their infrequent occurrence, nonspecific symptoms, and lack of distinguishing radiologic features, schwannomas are most often diagnosed histologically after surgical excision. We report herein a case of a perinephric, retroperitoneal schwannoma which, after evaluation by computed tomography, magnetic resonance, and angiography, appeared to be a renal cell carcinoma arising from the left kidney. The diagnosis of benign retroperitoneal schwannoma was made by histologic examination and immunohistochemical staining of the excised mass. A practical algorithm for perinephric, retroperitoneal schwannomas is proposed.

Key Words: schwannoma, renal tumor, retroperitoneal neoplasm, neurilemmoma, preoperative diagnosis

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Schwannomas are uncommon tumors originating from the Schwann cells of peripheral nerve sheaths. Less than 100 cases of retroperitoneal schwannomas have been reported in the world literature. (1) Approximately 3% of schwannomas are retroperitoneal, constituting some 4% of retroperitoneal tumors. (2) The most common site for these tumors is in proximity to the adrenal gland, (3) and only a single case of a retroperitoneal schwannoma presenting as a perinephric mass has been previously reported. (2) Although outcomes have generally been favorable, utilizing current imaging technology can lead to less invasive and more conservative surgical measures.

Case Report

A 63-year-old female presented for evaluation of left flank pain. Computed tomography (CT) revealed left renal and proximal ureteral stones with chronic obstructive uropathy. A well-defined, partially calcified solid mass, 8.5 cm in the greatest dimension, was also noted in the left retroperitoneum (Fig. 1). Magnetic resonance imaging (MRI) of the abdomen showed a hypointense and hyperintense mass on T1- and T2-weighted images, respectively. Enhancement with gadolinium revealed close attachment of the mass to the left kidney (Fig. 2). An angiogram demonstrated hypervascularity with contributions from the left renal artery (Fig. 3). Because of a high suspicion of carcinoma, the decision was made to perform a left nephrectomy and tumor resection after transcatheter arterial embolization of the left renal artery with two metallic coils.

The excised lobulated tumor had the consistency of soft tissue, weighed 200 g, and measured 9.5 X 7 X 5 cm, with multiple calcifications and a well-circumscribed margin. Sections of the tumor stained with hematoxylin and eosin revealed spindle cells with fibrosis and calcification (Fig. 4). No abnormal mitosis or pleomorphism was present. Masson's trichrome stain excluded a muscular source for the tumor. Immunohistochemical staining was positive for S-100 protein and alpha antichymotrypsin (AACT) and was negative for HHF35, CD34, and CD117, all of which was consistent with a schwannoma. There was no evidence of malignancy. The histologic and immunologic studies indicated no homology to the kidney, adrenal gland, or pancreas.

Discussion

Retroperitoneal schwannomas occasionally cause bony changes in the spine, but otherwise do not usually invade or obstruct adjacent structures. (4) However, schwannomas may cause compression of adjacent structures and have been associated with ureteral obstruction. (5) Furthermore, heterogeneity and cystic changes of schwannomas as demonstrated by MRI or CT have been reported as signs of malignancy, especially in patients with coexisting von Recklinghausen disease. (6)

Although diagnosis is often challenging, patients are usually diagnosed in the third through fifth decades, and there is an equal likelihood of occurrence in men and women. (7) Clinical presentation is variable and nonspecific. (1) Vague, poorly localized pain and discomfort in the abdomen or lower back are the most common symptoms. (6) Indeed, retroperitoneal schwannomas can mimic a variety of different conditions. (8-10)

Retroperitoneal schwannomas typically form large, well-circumscribed masses and frequently undergo cystic degeneration. (4) Preoperative radiographic imaging to assess cystic changes in the retroperitoneal schwannoma can be a useful adjunct to diagnosis. (11) Although not considered definitively diagnostic, features highly suggestive of retroperitoneal schwannoma on CT or MRI include the following: 1) a well-demarcated, round or oval mass with heterogeneous contrast enhancement due to the cystic and hemorrhagic changes; 2) calcification and cystic changes in a large tumor; and 3) iso- or slightly hyperintense signal intensity on T1-weighted images compared with muscle and high signal intensity on T2-weighted images. (1,12) MRI appears to be more specific and superior in delineating the tumor from adjacent anatomic structures. (1) Schindler et al (6) recommend the use of a fat suppression sequence to differentiate schwannomas from pure lipomatous tumors, given that schwannomas retain a high signal while lipomas do not. Hayasaka et al (13) reported that primary retroperitoneal schwannomas show different signal intensity characteristics, including cystic degeneration, but there are no absolute pathognomonic features of these tumors.

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Although Schindler et al (6) regard needle biopsy as the diagnostic gold standard, dissenting opinions exist. (1,7,9) On the other hand, Hughes et al (4) reached an accurate diagnosis using core biopsy in all of a series of 13 cases. In contrast, Gubbay et al (7) found core biopsy unhelpful in two such patients. Histologically, the presence of elongated bipolar spindle cells with zonally variable cellularity and a focally prominent nuclear pattern is suggestive of a schwannoma. (1) The absence of muscle can be verified with Masson's trichrome stain. Immunohistochemistry is useful in distinguishing schwannomas from other tumors. (1,15) Positivity for S-100 protein is fairly specific for schwannoma. Reaction to AACT does not appear to have been previously reported in this context but is nonspecific. Lack of reaction to HHF35, CD34, and CD117 is typical of schwannomas and helps to rule out most tumors with which schwannoma are confused.

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Conclusion

Schwannomas should be considered in the diagnosis of any retroperitoneal tumor. Appearance on MRI can be suggestive but is not diagnostic. While needle biopsy does not appear to have efficacy, core biopsy where feasible may provide a diagnosis. Treatment is by excision. Ideally, schwannomas should be extirpated with preservation of the associated nerve, and in the case of perinephric tumors, sparing the kidney. (1,2,7,14) The traditional approach has been via a laparotomy, but more recently, closed laparoscopic procedures have been met with success. (1,3,6,8) When possible, complete excision is the goal, but Schindler et al (6) recommend that if malignancy can be safely excluded, laparoscopic piecemeal excision can be considered. This should be as complete as possible but given the generally benign nature of the tumor and the possibility of serious operative morbidity, one should err on the conservative side. The final diagnosis is made on the basis of histologic and immunohistologic evaluation. Recurrence is unlikely and adjuvant therapy is rarely warranted.

References

1. Chew BH, Knudsen BE, Moussa M, et al. A retroperitoneal gastrointestinal schwannoma presenting as a perinephric mass. Can J Urol 2005;12:2555-2556.

2. Dede M, Yaqci G, Yenen MC, et al. Retroperitoneal benign schwannoma: report of three cases and analysis of clinico-radiologic findings. Tohoku J Exp Med 2003;200:93-97.

3. Funamizu N, Sasaki A, Matsumoto T, et al. Laparoscopic resection of a retroperitoneal schwannoma behind the lesser omental sac. Surg Lapa-rosc Endosc Percutan Tech 2004;14:175-177.

4. Hughes MJ, Thomas JM, Fisher C, et al. Imaging features of retroperitoneal and pelvic schwannomas. Clin Radiol 2005;60:886-893.

5. Sharma SK, Koleski FC, Husain AN, et al. Retroperitoneal schwannoma mimicking an adrenal lesion. World J Urol 2002;20:232-233.

6. Schindler OS, Dixon JH, Case P. Retroperitoneal giant schwannomas: report on two cases and review of the literature. J Orthop Surg 2002;10:77-84.

7. Gubbay AD, Moschilla G, Gray BN, et al. Retroperitoneal schwannoma: a case series and review. Aust N Z J Surg 1995;65:197-200.

8. Behrend M, Kaaden S, Von Wasielewski R, et al. Benign retroperitoneal schwannoma mimicking an adrenal mass. Surg Laparosc Endosc Percutan Tech 2003;13:133-138.

9. Hsiao WC, Lin PW, Chang KC. Benign retroperitoneal schwannoma mimicking a pancreatic cystic tumor: case report and literature review. Hepatogastroenterology 1998;45:2418-2420.

10. Kishi Y, Kajuwara S, Seta S, et al. Retroperitoneal schwannoma misdiagnosed as a psoas abscess: report of a case. Surg Today 2002;32:849-852.

11. Hettiarachchi JA, Finkelstein MP, Schwartz AM, et al. Benign retroperitoneal schwannoma presenting as a giant adrenal tumor. Urol Int 2003;71:231-232.

12. Nasu K, Arima K, Yoshimatsu J, et al. CT and MRI findings in a case of pelvic schwannoma. Gynecol Obstet Invest 1998;46:142-144.

13. Hayasaka K, Yamada T, Saitoh Y, et al. CT evaluation of primary benign retroperitoneal tumor. Radiat Med 1994;12:115-120.

14. Daneshmand S, Youssefzadeh D, Chamie K, et al. Benign retroperitoneal schwannoma: a case series and review of the literature. Urology 2003;62:993-997.

15. Lin CS, Hsu HS, Tsai CH, et al. Gastric schwannoma. J Chin Med Assoc 2004;67:583-586.

Ikuho Ohta, MD, Po-Hsun Lin, MD, Chuo-Li Rau, MD, and Kwei-Chin Wang, MD

From the Departments of Radiology, Uro-surgery, Surgery, and Pathology, Pao-Chien Hospital, Ping-Dong, Taiwan.

Reprint requests to Ikuho Ohta, MD, Department of Radiology, Pao-Chien Hospital, No. 123, Zhongshan Road, Ping-Dong City, 900, Taiwan. Email: [e-mail]

Accepted June 13, 2006.

RELATED ARTICLE: Key Points

* Schwannomas are rare tumors that are difficult to diagnose preoperatively.

* Evaluation of perinephric, retroperitoneal masses should preferably include magnetic resonance imaging rather than computed tomography.

* Core biopsies, but not needle biopsies, may assist in the preoperative diagnosis.

* Complete surgical excision is indicated and recurrence is rare.

* Histologic and immunohistologic staining should be used to confirm the diagnosis.