Specific Imaging Findings

Tuberculomas are ring-enhancing lesions that vary in size significantly from less than a centimeter to several centimeters in size. Although they are commonly found in the cerebral hemispheres, they may occur anywhere in the brain including the cerebellum and brainstem. On CT the lesion density varies and is surrounded by variable degrees of vasogenic edema. There is contrast enhancement of the capsule, while calcifications are seen in about 20% of tuberculomas. Occasionally the central aspect of the lesion contains an enhancing nodule or calcification giving rise to the so-called “target” sign, which is highly suggestive of tuberculoma. On MRI, tuberculomas with a necrotic center show low T1 and high T2 signal intensities, while those with a solid center show intermediate T1 and low T2 signal, along with low ADC values. Thick adjacent meningeal enhancement suggests the diagnosis. Thus an abscess-like lesion with low T2 centrally suggests tuberculosis or fungus. On magnetization transfer T1-weighted images the capsule is characteristically hyperintense. MRS findings show increased levels of lipids and lactate, low NAA and creatine with variable levels of choline, but no amino acids that are present in pyogenic abscess. Perfusion studies show low rCBV. Infarcts are common, especially in the “tubercular zone” – caudate nucleus, anterior thalamus, and anterior internal capsule.