Revisiting the CNS tuberculosis with emphasis on giant tuberculomas and introducing the "outer rim excrescence sign"

Central nervous system tuberculosis is a leading cause of morbidity and mortality in developing countries with Mycobacterium tuberculosis as the main etiological agent. Classical imaging findings pose no problem for diagnosis of CNS tuberculosis. Cases of giant or solitary ring enhancing lesions are increasing which mimic other infectious and noninfectious pathologies. This is a retrospective study of 40 patients (28 male and 12 female) of either surgically or clinically proven CNS tuberculosis. Solitary tuberculomas (ring or solid enhancing) were seen in 19 patients. Four patients showed presence of two to three lesions and the lesion more than one centimeter size was categorized as 'giant tuberculoma'. Multiple lesions with other associated findings were noted in 21 patients. Total 33 patients showed solitary or multiple ring enhancing lesions. Seven patients showed solid enhancing lesions (giant tuberculoma). The "Outer rim excrescence sign" was noted in a total of 16 patients. Both brain and spinal tuberculosis was noted in six patients. Seven patients presented with meningitis and hydrocephalous which is considered as the most common manifestation in the literature. Spinal leptomeningeal involvement was seen in five patients, whereas intramedullary cord tuberculomas were noted in four patients. Profound T2W hypointensity is a reliable predictor for giant tuberculomas with intense contrast enhancement, especially in deep locations. 'Outer rim excrescence' sign may contribute in cases of ring and solid enhancing lesions, however it requires further comprehensive study with MT Imaging and MR Spectroscopy to be recorded as a differentiating feature.