Fibrocaseous TB

Click to see other slides:    [1]   [2]   [3]   [4]

A 45 yr old woman complained of weight loss, fatigue, fever and night sweats for several months.  She coughed out blood recently.

1.    What is your diagnosis?

Pulmonary tuberculosis

3.    What are the main histological features?

            Central area of caseous necrosis

            Surrounded by thick fibrous wall (collagen deposition from fibroblasts)

            Giant cells are hardly visible

  3.    What are the 2 key pathological features in this condition that cause much morbidity and mortality?

Destruction of lung parenchymal tissue due to chronic granulomatous inflammation with release of proteases, elastases and other cytotoxic substances by the macrophages and T cytotoxic cells.

Erosion of tubercle into a vessel leading to hematogenous spread to other organs. 

4.    Relate the haemoptysis to the pathology.

      Erosion of a full patent vessel in the wall of a cavity

      Rupture of a dilated vessel in a cavity (Rasmussen�s aneurysm)

5.    What is the pathogenic mechanism for the necrosis?

      CD8+ suppressor T cells lyse macrophages infected with mycobacterium through a Fas-independent & granule dependent reaction

      CD8-4- (double negative) T cells lyse macrophages through a Fas-dependent reaction

      Direct toxicity of mycobacteria to macrophages

6.    What is the preferred site for the lesions?  Why?

Apical parts of the upper lobes (superior segments of lower lobes)

            High oxygen tension favours mycobacterial growth (obligate aerobes)

7.    How would you confirm your diagnosis?

Smear of sputum sample / biopsy specimen

Acid fast bacilli microscopy using Ziehl-Neelson stain

            Positive red coloured bacilli should be seen if sample is positive

8.    Where do you find non-caseating granulomas?

Sarcoidosis.

<< PREVIOUS            INDEX            NEXT SLIDE >>

Copyright � Joseph Ong 2003