Tuberculosis, Miliary

Martha Huller Maier, MD

Key Fact

Terminology

Fulminant infection with Mycobacterium tuberculosis disseminated via bloodstream

Imaging Findings

Nodules small and uniform in size, usually too numerous to count
- May have background of ground-glass opacities or septal thickening
Random distribution of nodules with respect to secondary pulmonary lobule
- Mild basilar predominance acutely
- Mild upper lung zone predominance chronically
Resolution complete with proper therapy or restoration of immune competence
Typical miliary lesions may not be visible radiographically until 3-6 weeks after hematogenous dissemination

Top Differential Diagnoses

Pathology

Clinical Issues

Lack of respiratory symptoms common
100% mortality if untreated
Miliary TB also seen after intravesical BCG immunotherapy for transitional cell carcinoma of bladder

Axial HRCT in this patient with miliary tuberculosis shows innumerable miliary nodules

, which have a random pattern of distribution.

Axial HRCT in the same patient more inferiorly shows miliary nodules

uniformly distributed throughout the lung.

TERMINOLOGY

Abbreviations and Synonyms

Definitions

Fulminant infection with Mycobacterium tuberculosis disseminated via bloodstream
- Typically a complication of primary infection with tubercle bacillus
- Less common in post-primary tuberculosis

IMAGING FINDINGS

General Features

Best diagnostic clue
- Innumerable small noncalcified nodules with random distribution
  - Distinct from endobronchial spread of infection, with tubercle bacillus resulting in tree-in-bud pattern of nodularity
Patient position/location
- Bilateral diffuse random distribution of nodules
- Mild basilar predominance acutely
- Mild upper lung zone predominance chronically
Size: Nodules < 5 mm diameter
Morphology: Fine rounded nodules: May be discrete or less well defined

CT Findings

Morphology
- Nodules small and uniform in size, usually too numerous to count
- Usually sharply marginated
- May have background of ground-glass opacities or septal thickening
- Nodules are diffuse and bilateral
- May have feeding vessel sign
Distribution
- Random distribution of nodules with respect to secondary pulmonary lobule
  - Not clustered into rosettes like centrilobular disease
- Profusion of nodules may be higher in lower lung zones acutely
  - Due to increased perfusion of lower lung zones
- Nodules may grow faster and become larger in upper lung zones with time
  - Due to increased oxygen concentrations in upper lung zones
Evolution
- Resolution complete with proper therapy or restoration of immune competence
Associated findings
- 30% of individuals with miliary disease may have other findings that suggest TB
  - Tuberculoma, lymphadenopathy, consolidation, effusion suggest miliary dissemination as result of primary TB
  - Calcified lymph nodes, cavitation, upper lobe fibrocavitary disease suggest miliary dissemination as result of post-primary TB

Radiographic Findings

Tiny nodules in miliary TB are too small (< 3 mm diameter) to be individually visualized radiographically
- Summation effect: Superimposition of lesions normally too small to be seen on radiographs; nodules summate to miliary pattern

Imaging Recommendations

Best imaging tool
- CT can demonstrate miliary disease before it becomes radiographically apparent
- Typical miliary lesions may not be visible radiographically until 3-6 weeks after hematogenous dissemination
- 25-40% of affected individuals have normal chest radiographs at initial presentation

DIFFERENTIAL DIAGNOSIS

Metastases

Common metastases presenting with miliary pattern
- Thyroid cancer
- Melanoma
- Choriocarcinoma
- Renal cell carcinoma
- Breast cancer
Metastatic nodules tend to be slightly larger, more well defined than those of miliary tuberculosis
- Tend to vary more in size than those of miliary tuberculosis