Intraoperative Consultation for a Spinal Cord Mass
A 45-year-old woman undergoes laminectomy for a 2.5 cm intramedullary mass at T8. The surgeon requests frozen section to guide the extent of resection. The tissue is gray-white and firm. On frozen section, you see a moderately cellular spindle cell proliferation with Rosenthal fibers and eosinophilic granular bodies. There is no necrosis or microvascular proliferation. The surgeon asks whether to proceed with gross total resection or to stop after biopsy. You have 10 minutes to decide.
1. What is your intraoperative diagnosis, and how does it influence the surgical decision?
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The features are consistent with pilocytic astrocytoma, a WHO grade I tumor. In the spinal cord, pilocytic astrocytoma is often well-circumscribed and may be amenable to gross total resection if safe. However, because it is intramedullary, aggressive resection risks neurologic deficit. The intraoperative diagnosis should be communicated as 'low-grade glial neoplasm, favor pilocytic astrocytoma.' The surgeon should weigh the benefit of resection against neurologic risk; if the tumor is not clearly separable from normal cord, a subtotal resection or biopsy is acceptable, with the plan for adjuvant therapy if needed. The frozen section helps avoid unnecessary radical resection.
2. What pitfalls should you consider in interpreting this frozen section?
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Pitfalls include: 1) Rosenthal fibers can be seen in reactive gliosis, but the combination with eosinophilic granular bodies and a biphasic pattern supports pilocytic astrocytoma. 2) Frozen section artifact can mimic atypia. 3) The sample may be small and not representative; if the tumor is a diffuse astrocytoma, gross total resection would be inappropriate. 4) The presence of eosinophilic granular bodies is not entirely specific. Therefore, the diagnosis should be framed as 'favor' rather than definitive, and permanent sections with immunohistochemistry (GFAP, IDH1, BRAF) should be awaited. Communication with the surgeon should include the caveat that a definitive diagnosis requires permanent sections.