Tuberculosis (summary)

This is a basic article for medical students and other non-radiologists

Tuberculosis (TB) is a mycobacterial multisystemairborne infection that often affectsis typically asymptomatic in children but can reactivate in later life causing a destructive cavitating contagious pneumonia. Occasionally TB spreads through the lungs. It may be a primary tuberculous infection, secondary infection or appear as chronic scarring. TB may also be seen on a chest x-ray as lymphadenopathybloodstream to infect the brain and other organs.

Reference article

This is a summary article; read more in our article on tuberculosis.

Summary

• epidemiology

  • developing nations - adolescents and young adults

  • developed nations - immigrants, homeless and HIV-infected

  • globally TB causes more deaths than any other infectious disease

• presentation

  • ​primary infection

    • usually asymptomatic

    • may feel generally unwell or have a small pleural effusion

  • post-primary infection

    • when patients usually present to clinicians

    • non-specific systemic symptoms

      • malaise

      • weight loss

      • fever

      • night sweats

    • pulmonary symptoms

      • productive cough (mucopurulent or blood-stained)

      • shortness of breath

      • chest pain

    • extrapulmonary symptoms

      • variabledepends on location of lesionsdisease

• pathology

  • M. tuberculosis

    • aerobic mycobacterium

    • Gram staining ineffective due to waxy coating

  • primary infection

    • non-immune host exposedfirst exposure to M. tuberculosis

    • primary lesion usually occursthe lung infection may be occult or may be visible as an area of consolidation in the upper region of the lung

      • mid or lower zone (Ghon focus describes the initial granulomatous lesion )

    • Ghon complex is the calcified focus with associated mediastinalmore commonly hilar and/or paratracheal lymphadenopathy are seen

    • most primary infections result in healingare asymptomatic and are contained remaining dormant (latent TB)

    • leadsoccasionally the host immune system does not contain the bacterium leading to post-primary immunity and latent infectionprogressive primary TB or haematogenous spread (miliary TB)

• post-primary TB is due to reactivation of infection (secondary tuberculosis)when the immune system is impaired due to old age, immunosuppressive drugs, etc.

  • dormant bacteria are no longer contained and multiply in the lungs causing:

    • harboured bacteria is reactivated after primary infection

      • occurs in immunocompromised individuals (e.g. HIV, steroid therapy, cytotoxic drugs)

    • lung infection causes patchy consolidation or cavitation a contagious destructive cavitating pneumonia

    • extrapulmonary infection may involve meninges, bones, lymph nodes, urinary tract or GI tractendobronchial spread within the lungs

• miliary tuberculosis

  • disseminated disease from TB infectionspreads through the blood

  • tuberculomas in immunocompromised patientsbrain, kidney, bone, etc

  • tuberculous meningitis

  • may follow primary or post-primary infection

• poor prognosis

Radiographic features

Chest radiograph

• primary infection

  • parenchymal consolidation

  • lymphadenopathy - most frequent manifestation

  • pleural effusion

  • Ghon complex (consolidation plus lymphadenopathy)

• post-primary infection

  • patchy consolidation (upper zones)

  • cavitation

  • healing results in fibrosis

  • pleural disease and calcification

• miliary tuberculosis

  • innumerable 1-3 mm diameter miliary nodules

  • uniform size and distribution throughout both lungs

• extrapulmonary tuberculosisspine infection

  • tuberculoma within an affected organ

  • widely variable

CT chest

As with most chest pathology, CT shows the same findingsis far more sensitive and demonstrates lesion characteristics which are helpful in diagnosis:

• central necrosis in lymph nodes

• areas of consolidation which may be occult on CXR

• effusions

• empyema

• cavitation

• endobronchial spread (tree in bud opacities)

• miliary nodules

• signs of latent disease such as demonstrated on the chest radiograph, but with more detailcalcified granulomata and clarify. Smaller nodules can be seen. Lymph nodes can be assessed in more detail.upper zone fibrocalcific disease