Diagnostic Neuropathology and Patient Care Consultation
The diagnostic mindset
Neuropathology questions test pattern recognition plus communication. You are not only rendering a diagnosis but advising clinicians on prognosis, molecular testing, and follow-up.
Concepts to know:
- Tumor classification: WHO grading integrates histology and molecular markers (IDH, 1p/19q, MGMT, H3 K27M). Know that grade is not solely mitotic-count based.
- Glioblastoma vs metastatic carcinoma vs lymphoma: necrosis with pseudopalisading, vascular proliferation (GBM); cohesive nests with desmoplasia (metastasis); angiocentric atypical lymphoid cells (CNS lymphoma).
- Demyelinating vs neoplastic: demyelination shows relative axonal preservation and macrophage-rich rims; beware the trap of calling it glioma.
- Infection and inflammation: granulomatous, viral inclusions, prion spongiform change.
- Consultation etiquette: frozen section limits, need for permanent sections and ancillary studies, and clear communication of uncertainty.
Traps:
- Calling a pilocytic astrocytoma malignant because of Rosenthal fibers or microcysts - it is grade 1.
- Overcalling reactive gliosis as infiltration; use GFAP and IDH/other markers thoughtfully.
- Ignoring molecular data that reclassify a tumor (e.g., IDH-wildtype diffuse astrocytoma behaving as GBM).
Worked example: A frontal mass in a 60-year-old shows necrosis and microvascular proliferation. You diagnose glioblastoma. The consult question is whether to send IDH and MGMT. Answer: yes - IDH status confirms classification and MGMT informs temozolomide response. Always state limitations of frozen section and recommend permanent/molecular confirmation.