Question

Which of the following imaging modalities is most sensitive to detect early renal tuberculosis?

• A. IV urography
• B. Ultrasound
• C. Computed tomography
• D. MRI

Hint:

CT images the kidney parenchyma directly and picks up small papillary and calcification changes of renal TB earlier than a urogram.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
Early renal tuberculosis causes subtle changes such as small papillary necrosis, tiny calyceal irregularities, and fine parenchymal calcification, well before the kidney is grossly scarred. We need the imaging test best able to pick these subtle early findings up.

Step 2: Key Concept:
Intravenous (IV) urography shows the collecting system through excreted contrast and was, for decades, the traditional way to look for the moth-eaten calyces of renal TB. Computed tomography, however, images the renal cortex, medulla, and calcifications directly in cross-section, which lets it pick up small parenchymal cavities, scarring, and calcifications earlier and more clearly than a urogram, which only shows the collecting system outline.

Step 3: Detailed Explanation:
Ultrasound is useful and radiation-free for follow-up, but it is operator-dependent and not sensitive enough to catch the earliest, small parenchymal lesions of renal TB, so option (B) is not the best answer.
MRI gives good soft tissue contrast, but it is less sensitive than CT for detecting the small calcifications that are an important early clue to renal TB, so option (D) is not the best answer.
IV urography can miss early parenchymal disease because it depends on functioning renal tissue and a patent collecting system to show contrast, and subtle cortical lesions or small calcifications may not distort the calyces enough to be seen this way, so option (A) is not the most sensitive test for early disease.
CT, and specifically CT urography, directly visualises the renal parenchyma, so it detects small papillary necrosis, calyceal wall irregularity, thinned cortex, and calcification earlier than IV urography can, making option (C) the most sensitive choice for early renal tuberculosis.

Step 4: Final Answer:
Computed tomography is the most sensitive modality for detecting early renal tuberculosis.
\[ \boxed{\text{Computed tomography}} \]
Note: the original 2002 answer key marks IV urography, which was the standard reference test at that time. Current radiology teaching, with CT urography now widely available, holds CT to be more sensitive than IV urography for picking up early renal TB changes, so this solution follows the updated answer.