Image of the Month—Diagnosis

Exploratory laparotomy revealed a mass, likely arising from the left adrenal gland, without any signs of infiltration of the pancreas (Figure 2). A left adrenalectomy was performed en bloc with the aforementioned lesion. At pathologic evaluation, the mass was clearly separated from the adrenal gland by a fibrous pseudocapsule. Results of histologic and immunohistochemical examination (intense staining for S100 using the alkaline phosphatase–anti–alkaline phosphatase method) were consistent with the diagnosis of schwannoma. At 65 months of follow-up, the patient was doing very well, with no signs of local or distant recurrence on a computed tomographic scan.

Schwannomas are a rare group of soft tissue tumors originating from the peripheral nerve sheath; they can occur anywhere neural tissue with Schwann cells is present, but most of them arise in the head and neck region or in the upper and lower extremities. Localization in deeper structures, such as the posterior mediastinum or retroperitoneum, is unusual. Retroperitoneal forms, in fact, account for only 0.7%-2.7% of all schwannomas¹and 0.5%-1.2% of all retroperitoneal tumors.²Because of the flexibility of the retroperitoneum, tumors grow to a large size before becoming symptomatic. When apparent, clinical signs or symptoms are generally vague and nonspecific, as a consequence of adjacent organ compression or infiltration; therefore, detection is often accidental. Schwannoma typically appears as a solitary, well-encapsulated, firm, and smooth-surfaced round mass. In large tumors (>8-10 cm), a degenerative pattern (cystic areas, calcifications, interstitial fibrosis, and hyalinization) is commonly found that identifies the “ancient” variant.³

Retroperitoneal schwannomas generally have a benign biological behavior. Malignant forms usually develop ex novo because transformation of benign lesions is rather infrequent.⁴Whereas benign schwannomas tend to displace surrounding structures without invading them, malignant ones show the same biological features of undifferentiated sarcomas, with locally invasive growth and distant metastatic diffusion.

Preoperative diagnosis of retroperitoneal schwannomas is not easy owing to the difficulty in finding imaging features (with ultrasonography, computed tomography, or magnetic resonance imaging) that enable the discrimination of schwannomas from other soft-tissue tumors (fibrosarcoma or liposarcoma) and benign forms from malignant ones.⁵Schwannomas can frequently be misdiagnosed as psoas abscesses, pancreatic cysts or neoplasms, adnexal masses, or adrenal, kidney, or hepatic tumors, as reported in the literature.^6-9However, radiologic imaging is helpful in therapeutic planning, as it gives information about the tumor's size, location, and possible invasion of other structures. Fine-needle aspiration biopsy may theoretically be useful if Schwann cells are found in the sample, but the tissue specimen collected for diagnosis is often inadequate and may be misleading because of cellular pleomorphism in degenerated areas, which might be interpreted as consistent with malignancy.¹⁰

Surgery is considered the best treatment for retroperitoneal schwannomas, as their response to radiation and chemotherapy is poor. Imaging, intraoperative macroscopic evaluation, and frozen section analysis are not valid or accurate indicators of malignancy, so a definitive diagnosis of the tumor's nature can be obtained only with a careful histologic and immunohistochemical examination. Considering the possibility of a misdiagnosed malignant lesion and a local recurrence rate of 10% to 20% also in benign schwannomas (probably due to incomplete excision), the optimal management should be a radical exeresis with clear margins, whenever feasible, eventually including in the resection adjacent structures.^3,10After complete removal, long-term survival can be attained.

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Correspondence:Antonio Pio Tortorelli, MD, Department of Surgical Sciences, Digestive Surgery Unit, Istituto di Clinica Chirurgica, Catholic University School of Medicine, Largo A. Gemelli, 8, 00168 Rome, Italy (dr_aragorn78@yahoo.it).

Accepted for Publication:November 23, 2005.

Author Contributions:Study concept and design: Tortorelli. Acquisition of data: Papa and Rosa. Analysis and interpretation of data: Pacelli and Doglietto. Drafting of the manuscript: Rosa. Critical revision of the manuscript for important intellectual content: Tortorelli, Papa, Pacelli, and Doglietto. Administrative, technical, and material support: Rosa. Study supervision: Tortorelli, Papa, Pacelli, and Doglietto.

Financial Disclosure:None reported.