Diagnostic Challenges of Retroperitoneal Intranodal Schwannoma Presenting as an Adrenal Mass

Primary intranodal spindle cell lesions encompass a variety of uncommon tumors. Schwannoma is an easily recognizable peripheral nerve sheath tumor having characteristic pathologic features. Primary intranodal schwannoma is diagnostically challenging because its occurrence in lymph nodes is rare, unexpected and may present with atypical modified and misleading pathologic features. Nodal schwannomas can be confused with other primary nodal and metastatic spindle cell tumors Distinction is clinically important because intranodal schwannoma is completely cured by excision, whereas other spindle cell tumors may require further management options depending on their types. We report schwannoma occurring in a retroperitoneal lymph node in 72-year-old man who was found to have an adrenal mass. The effaced lymph node was replaced by a 5.0 cm nodular spindle cell tumor with varying cytoarchitectural growth patterns simulating a variety of spindle cell lesions. The periphery showed a rim of compressed residual nodal lymphoid tissue. The initial differential diagnosis was wide. It included the more common spindle cell lesions anticipated to occur within lymph nodes. Because schwannoma was unexpected, it was not initially considered in the differential diagnosis. However, the diagnosis of schwannoma was confirmed by an intense staining for S-100, and a negative staining for immunomarkers specific to other spindle cell tumors. The final diagnosis was a sporadic intranodal schwannoma. Intranodal schwannomas should be considered in the differential diagnosis of spindle cell lesions occurring in lymph nodes. Certain histopathologic features are helpful clues to avoid pitfalls. The final diagnosis depends on interpretation of relevant positive and negative immunomarkers.