The Characteristic “Tunnel Sign” on MRI as a Diagnostic Marker of Tunneling Abscesses in Listeria Rhombencephalitis in a Patient With Multiple Myeloma: A Case Report

Neurolisteriosis is a rare but potentially serious CNS infection. Diagnosis can be established through bacteriological studies or by identifying characteristic tunneling abscesses in the CNS. Delayed initiation of appropriate antibiotic therapy may result in permanent structural brain damage, disability, or death. We report the case of a 65-year-old woman with multiple myeloma undergoing chemotherapy who presented with an acute febrile illness accompanied by drowsiness, slurred speech, difficulty swallowing, neck stiffness, and complex ophthalmoplegia. MRI of the brain demonstrated characteristic findings of the "tunnel sign," suggestive of a tunneling abscess in <i>Listeria</i> rhombencephalitis. The diagnosis was made based on radiological features alone, in the absence of microbiological confirmation. With prompt initiation of IV ampicillin, she demonstrated marked neurological recovery, with some residual deficits.