A 58-year-old man presents with headache, confusion, and a ring-enhancing lesion in the right frontal lobe on MRI with significant perilesional edema. He has no fever, no immunocompromise, and no history of known malignancy. Spectroscopy shows high choline:creatine ratio with reduced N-acetyl aspartate. The most likely diagnosis and primary next investigation is:

• A Glioblastoma multiforme (GBM); CT chest-abdomen-pelvis to exclude systemic primary followed by stereotactic biopsy ✓
• B Primary CNS lymphoma; do not use steroids before CSF analysis and stereotactic biopsy
• C Brain abscess; blood cultures and LP before neurosurgical drainage
• D Metastatic carcinoma; systemic workup (CT-CAP + PET) before biopsy

Explanation

Ring-enhancing lesion in an older non-immunocompromised patient with high choline:NAA ratio and marked edema is most consistent with glioblastoma multiforme (WHO Grade IV astrocytoma). Without a known primary, systemic staging with CT chest-abdomen-pelvis (to exclude metastatic cancer) is performed, but stereotactic biopsy is required for tissue diagnosis regardless. GBM has median survival of 15 months with Stupp protocol (temozolomide + radiotherapy). Primary CNS lymphoma is also ring-enhancing but steroids before biopsy can cause 'melting tumor' phenomenon, falsely negative biopsy. Brain abscess in a non-immunocompromised patient typically presents with fever and infection source.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.