A 24-year-old woman from a high TB-burden country presents with 8 weeks of low-grade evening fever, night sweats, anorexia, and 6 kg weight loss. Chest examination is unremarkable; sputum AFB smear is negative. Contrast-enhanced CT chest shows enlarged right paratracheal, subcarinal, and hilar lymph nodes (largest 28 mm). The structure marked **C** demonstrates central low-attenuation (hypodense) core with peripheral rim enhancement and nodal matting. EBUS-TBNA confirms granulomatous inflammation with caseation and acid-fast bacilli on Ziehl-Neelsen stain. GeneXpert MTB/RIF is positive and rifampicin-sensitive. Which of the following BEST explains the radiological appearance of the structure marked **C**?
A. Peripheral calcification with central lipid-rich debris from treated lymphoma
B. Homogeneous nodal enlargement due to lymphoid proliferation without necrotic change
C. Symmetric bilateral hilar adenopathy with non-caseating granulomas and elevated serum ACE
D. Central caseous necrosis surrounded by peripheral granulation tissue and inflammatory vascularity
Explanation
Why "Central caseous necrosis surrounded by peripheral granulation tissue and inflammatory vascularity" is right
The structure marked C shows the pathognomonic CT signature of tuberculous lymphadenitis: a hypodense (low-attenuation) central core representing caseous necrosis, with peripheral rim enhancement reflecting granulation tissue, inflammatory cells, and neovascularization. This appearance is highly specific for TB lymphadenitis and is the most common form of extrapulmonary TB in HIV-negative young adults. The positive AFB smear and GeneXpert MTB/RIF confirm Mycobacterium tuberculosis with caseating granulomatous inflammation, which is the hallmark pathological correlate of the imaging finding (WHO TB Guidelines 2024).
Why each distractor is wrong
Homogeneous nodal enlargement due to lymphoid proliferation without necrotic change: This describes lymphoma, which presents as bulky, homogeneous nodes WITHOUT central necrosis or rim enhancement. Lymphoma lacks the caseous center and does not show the characteristic hypodense-to-enhancing pattern seen in C.
Peripheral calcification with central lipid-rich debris from treated lymphoma: While treated lymphomas and metastatic adenocarcinomas may show calcifications, they do NOT exhibit the acute caseating necrotic pattern with active rim enhancement seen in C. Calcification is a late finding in chronic TB, not the acute presentation here.
Symmetric bilateral hilar adenopathy with non-caseating granulomas and elevated serum ACE: This describes sarcoidosis (the '1-2-3 sign' of Garland), which presents with NON-caseating granulomas and is NOT associated with central necrosis, rim enhancement, or acid-fast bacilli. Sarcoidosis is a key differential but is excluded by the positive AFB and caseating histology.
High-YieldNEET PG
The CT triad of tuberculous lymphadenitis is central hypodensity (caseation) + peripheral rim enhancement + nodal matting/conglomeration—this distinguishes TB from sarcoidosis (non-caseating, symmetric), lymphoma (homogeneous, no necrosis), and metastatic disease (calcified, no active inflammation).
WHO TB Guidelines 2024; classic TB imaging and pathology
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