Contributed by Mee Joo, MD, PhD1, Song-Hee Han, MD1, Sun Hee Chang, MD, PhD1, Hanseong Kim, MD, PhD1, Byung Hoon Lee, MD2, Moon Jun Sohn, MD, PhD3
Department of 1Pathology, 2Radiology and 3Neurosurgery, Inje University Ilsan Paik Hospital, Goyang, South Korea
A 69-year-old woman presented with a 2-month history of progressive bilateral leg weakness and gait difficulty. On examination, the patient had diffuse lower extremity weakness and hypesthesia of the left leg. Magnetic resonance imaging revealed a 2.9-cm, extradural, soft tissue mass at the T5-6 level, with spinal cord compression; the mass was hypointense on a T1-weighted image (Figure 1) and hyperintense on a T2-weighted image (Figure 2). The tumor was a relatively well-demarcated epidural mass with focal invasions into both facet joints. Intraoperative examination showed a neoplasm with clear and granular cell morphologies displaying solid, papillocystic, and follicular patterns. Postoperative 18F-fluoro-2-deoxy-D-glucose positron emission tomography-computed tomography (CT) and neck CT failed to identify a primary tumor or any other lesions.
Histologically, the tumor showed various histologic patterns consisting of round to polygonal cells with abundant cytoplasm and small, round, uniform nuclei. The predominant growth pattern was solid with sheets or nests separated by fibrovascular stroma (Figure 3). Some tumor cells formed papillary folds interspersed with cystic spaces, forming a so-called "papillocystic" pattern (Figure 4). Further, there were epithelial-lined cystic spaces filled with eosinophilic, proteinaceous materials, resembling thyroid follicles (Figure 5). Most of the tumor cells had abundant, clear, vacuolated cytoplasm with distinct cell borders. In addition, nests of granular cells with abundant basophilic to amphophilic, fine to coarse granules were mixed with more eosinophilic ductal cells, forming microcysts (Figure 6). The cytoplasmic granules were periodic acid-Schiff (PAS)-positive and diastase resistant. Neither whorl formation nor psammoma bodies were seen. Tumor necrosis was absent, and mitotic figures were rare. Immunohistochemically, the tumor cells were positive for cytokeratin AE1/AE3 (Figure 7) and alpha-1-antitripsin (Figure 8) and negative for S-100 protein, CD10, thyroid transcription factor-1 (TTF-1), gross cystic disease fluid protein-15 (GCDFP-15), vimentin, and synaptophysin. What is the diagnosis?