Page 175 - Concise Pathology for Exam Preparation ( PDFDrive )

160 SECTION I General Pathology

drain through lymphatics into lymphatic ducts, which empty into the right side of
heart and then into pulmonary arteries. When the dissemination involves only lungs,
it is called miliary pulmonary tuberculosis. Systemic miliary tuberculosis ensues
when infective foci in lungs seed pulmonary venous return to the heart; the organ-
isms subsequently disseminate through systemic arterial system. Almost every organ
in body can be seeded.
• Isolated-organ tuberculosis is a consequence of haematogenous seeding and organs
that are typically involved include meninges (tuberculous meningitis), genital or-
gans and urinary tract (genitourinary tuberculosis), adrenals (formerly an impor-
tant cause of Addison disease) and bones (osteomyelitis). When vertebrae are
affected, the disease is referred to as Pott disease. Paraspinal ‘cold abscesses’ in these
patients may track along tissue planes to present as an abdominal or pelvic mass. The
most common type of extra pulmonary tuberculosis is lymphadenitis and it most
frequently involves the cervical region. The usual presentation is that of discharging
sinuses with an underlying cervical swelling (‘scrofula’). The lymph nodes are in-
volved as a consequence of lymphatic spread.

Microscopy
Epithelioid cell granulomas with or without caseation are the histological hallmark of tu-
berculous disease. These granulomas are usually enclosed within a fibroblastic rim. Multi-
nucleate giant cells called ‘Langhans giant cells’ are present in the granuloma along with
mononuclear cells including lymphocytes, plasma cells and histiocytes. Immunocompro-
mised individuals do not form well-defined granulomas and may manifest with ill-formed
aggregates of histiocytes and chronic inflammatory cells (see Chapter 2).
The differences between primary and secondary tuberculosis are listed in Table 7.2.
Diagnosis
1. Demonstration of AFB on microscopic examination of a diagnostic specimen (spu-
tum or tissue): Smears or tissue slides stained with Ziehl Neelsen stain are examined
for AFB. This method has a relatively low sensitivity (40–60%) in confirmed cases of
pulmonary tuberculosis. Auramine-rhodamine staining and fluorescence micros-
copy can improve the sensitivity to a certain extent. Three sputum specimens, prefer-
ably collected early in the morning, should be submitted to the laboratory for AFB
smear and mycobacterial culture.
2. Culture: Besides sputum and tissue, other specimens which can be used for culture are
body cavity fluids, urine or gastric lavage fluid. Specimens may be inoculated onto egg-
or agar-based medium (eg, Löwenstein–Jensen or Middlebrook 7H10) and incubated
at 37°C. M. tuberculosis grows slowly (4–8 weeks). A presumptive diagnosis can be

TABLE 7.2. Differences between primary and secondary tuberculosis

Features Primary TB Secondary TB
Evolution Seen in individuals who have not Occurs due to reactivation of a primary focus
of disease been previously sensitized to tu- or reinfection
bercle bacilli
Age group Common in children/individuals of Any age (usually occurs later than primary
affected younger age; may be seen in adults infection)
in developed countries
Distribution Lower part of upper lobe and upper Apex of one or both lobes due to high oxygen
part of lower lobe tension in apices
Lesion Ghon focus Simon focus
Involvement Early involvement of lymphatics and Due to pre-existing hypersensitivity, bacilli
of lymphatics lymph nodes induce an immediate tissue response that
walls off the lesion and prevents early in-
volvement of lymphatics and lymph nodes
Severity Generally asymptomatic, less severe Usually symptomatic, more severe

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