A ring-enhancing lesion is an abnormal imaging finding on Magnetic Resonance or Computed Tomography scanning using intravenous radiocontrast.
A 34-year old worker was found by his co-workers as having repeated attacks of Generalized tonic- clonic convulsions with loss of consciousness. The paramedics arrived on the scene and gave the loading dose of anticonvulsants by the intravenous route but the seizures continued unabated. A diagnosis of Status epilepticus was made and he was intubated and shifted to the intensive care. The Magnetic Resonance imaging revealed a ‘ring’lesion in the left Parietal lobe.
Prof. Gaillard listed the differential for these ‘peripheral’ or ‘ring’ enhancing brain lesions as:
Subacute infarct / haemorrhage / contusion
Demyelination (incomplete ring)
Tumefactive demyelinating lesion (incomplete ring)
Lymphoma (in immunocompromised patient)
Many features of the lesion as well as clinical presentation and patient demographics need to be taken together to help narrow the differential. Our patient was from the Indian subcontinent and had received a 4-months course of anti-tubercular treatment for pulmonary tuberculosis one year back. The MR appearance of the lesion resembles a ‘crenated’ RBC appearance which is more suggestive of CNS tuberculosis than a pyogenic abscess. He responded to four drug anti-tubercular drug regimen.
No single feature is pathognomonic, although a cystic lesion that markedly restricts centrally (the fluid component) on MR Diffusion Weighted Imaging (DWI) should be considered an abscess until proven otherwise. In patients with HIV, the major differential is between CNS lymphoma and CNS toxoplasmosis which accounts for almost 70% of ring enhancing lesions in these patients.