Target sign in hepatic tuberculosis

Discussion:

This case demonstrates hepatic involvement in a patient with disseminated tuberculosis (TB) with Pott disease. Biopsy of one of the hepatic lesions showed necrotizing granulomatous inflammation in keeping with TB.

TB of the liver is uncommon and accounts for less than 1% of all tuberculous infections. Hepatic TB can occur primarily or it can be secondary to a tubercular focus elsewhere in the body. In imaging, it presents with different appearances and can mimic a variety of other conditions. Hepatic TB can be comprehensively classified into micronodular and macronodular forms. Micronodular hepatic TB refers to miliary tuberculosis wherein the lesions measure 0.5 - 2 mm in diameter. The macronodular form may present either as multiple 1 - 3 cm lesions or as a large tumorlike mass. Some macronodular lesions may exhibit a bull’s-eye appearance (“Target” sign), which refers to the central nidus of calcification or central enhancement with surrounding area of low attenuation or ring of enhancement on CT, or central enhancement accompanied by peripheral rim enhancement on post-contrast MRI. This sign is suggestive of, but not pathognomonic for, TB. Image-guided biopsy is often required to obtain a definitive histological diagnosis.

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