“Target Sign” on MRI: A Thoracic Intramedullary Tuberculous Abscess Presenting as Paraparesis in an Immunocompromised Setting

In immunocompromised patients like HIV, tuberculosis (TB) is the most common opportunistic infection worldwide.[1] Around 8% of them present with musculoskeletal involvement and 50% involve the spine.[2] Common forms of spinal TB are tuberculous spondylitis, TB myelitis, and intraspinal TB. Intramedullary spinal tuberculomas (IMTs) are rare, even in geographic areas where TB is endemic.[4] A 32-year-old male, a known case of acquired immunodeficiency syndrome (AIDS), on irregular ART, presented to us with progressive weakness of both lower limbs leading to difficulty in walking, and getting up from lying down position for the last 6 months. For the last 2 months, he was bedbound due to the progression of his condition with incontinent bladder and bowel. He was diagnosed as having pulmonary tuberculosis (PTB) and was Anti-Tubercular Treatment (ATT) regularly. MRI of the spine showed a “Target Sign” in sagittal and axial sections of the thoracic spine in T2-weighted images [Figure 1a and b] at the D8 level. On contrast enhancement, the lesion appeared as a uniformly enhancing ring-like lesion [Figures 2, 3a and b]. Laminectomy with excision of the lesion was performed, which turned out to be a tuberculous abscess, on histopathology examination [Figure 4].Figure 1: (a) T2-weighted sagittal section of thoracic spine showing Target Sign at the level of D8 vertebral body with hyperintense signal surrounding the lesion extending till D4 superiorly and D12 inferiorly. (b) T2-weighted image of axial section of the spine at the level of D8 showing characteristic “Target Sign”Figure 2: Contrast-enhanced T1-weighted sagittal section of the thoracic spine showing uniformly ring enhancing lesion at the level of D8 levelFigure 3: (a) Contrast-enhanced T1-weighted coronal section of the thoracic spine showing uniformly ring enhancing lesion at the level of D8 level. (b) contrast-enhanced T1-weighted axial section of the thoracic spine showing uniformly ring enhancing lesion at the level of D8 levelFigure 4: Granulation tissue taken out during the intraoperative period which was sent for biopsy confirmed tubercular pathologyThe advent of MRI has made diagnosis of IMT more accurate and earlier. In the early phase, the tuberculoma is characterized by a severe inflammatory reaction with a gel capsule not well formed, and T1WI and T2WI show equal signal intensity. As the gel content in the tuberculoma increases, the peripheral edema begins to disappear, T1WI shows isointense lesions while T2WI shows hypointense lesions. On T2WI, the caseous substance appears hyperintense at the center, which gives the characteristic Target Sign.[3] Compliance with the treatment regimen should be emphasized to this patient population, who suffer dual infection and a host of other secondary infections as well as malignancies due to the immunocompromised status. The “Target Sign” is a valuable indicator that helps to differentiate spinal tuberculoma from other intramedullary lesions. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.