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114 Tuberculosis
from other acid-fast organisms, such as other mycobacterial organisms any intussusception. Enteroliths, mottled calcification in the mesen-
or Nocardia species. It can give a quantitative assessment of the num- teric lymph nodes, and any evidence of ascitis may be suggested on
ber of bacilli being excreted (e.g., 1+, 2+, 3+). For a reliable positive the plain film.
result, smears require approximately 10,000 organisms per milliliter. Contrast Studies
Therefore, the results may be negative in early stages of the disease or Barium meal and enema are together positive in 80–85% of the cases
with sparse bacilli. A single organism on a slide is highly suggestive of GI tuberculosis.
and warrants further investigation.
• Small bowel barium meal: The radiologic findings that may be
Mycobacterium Culture seen on a small bowel study include:
Culture of M. tuberculosis is the definitive method to detect bacilli and
is more sensitive than examination of the smear. Approximately 10 - mucosal irregularity and rapid emptying (ulcerative);
AFB per millimeter of a digested concentrated specimen are sufficient - flocculation and fragmentation of barium (malabsorption);
to detect the organisms by culture. A culture also allows identification - stiffened and thickened folds;
of specific species and testing for drug sensitivity. Due to the emer- - luminal stenosis with smooth but stiff contours (“hour glass-
gence of multidrug-resistant (MDR) organisms, determination of the stenosis”);
drug sensitivity panel of an isolate is important so that appropriate - dilated loops and strictures;
treatment can be ensured.
M. tuberculosis is a slow-growing organism, however, so a period - displaced loops (enlarged lymph nodes); and
of 6–8 weeks is required for colonies to appear on conventional culture - adherent fixed and matted loops (adhesive peritoneal disease).
media. Conventional solid media include the Löwenstein-Jensen • Barium enema: The following characteristics may be seen:
medium, which is egg based, and the Middlebrook 7H10 and 7H11
media, which are agar based. Liquid media (e.g., Dubos oleic-albumin - spasm and oedema of the ileocaecal valve (early involve-
media) also are available, and they require incubation in 5–10% carbon ment); characteristic thickening of the ileocaecal valve lips
dioxide for 3–8 weeks. or wide gaping of the valve with narrowed terminal ileum
(“Fleischner” or “inverted umbrella sign”);
Nucleic Acid Techniques
- “conical caecum”, a deformed and pulled-up caecum due to
Nucleic acid techniques include nucleic acid probes and polymerase
contraction and fibrosis;
chain reaction (PCR). Although their sensitivity and specificity in
smear-positive cases exceed 95%, the sensitivity of smear-negative - increased (obtuse) ileocaecal angle and dilated terminal
cases varies from 40% to 70%. ileum, appearing suspended from a retracted, fibrosed caecum
(“goose neck deformity”) ;
• Nucleic acid probes help advance identification of the M. tubercu-
losis complex. Sensitivity and specificity approach 100% when at - deformed and incompetent ileocaecal valve;
least 100,000 organisms are present. - “purse string stenosis”—localised stenosis opposite the ileo-
caecal valve with a rounded-off smooth caecum and a dilated
• PCR nucleic acid amplification tests allow the direct identification of
M. tuberculosis in clinical specimens, unlike nucleic acid probes, which terminal ileum ;
require substantial time for bacterial accumulation in broth culture. - “Stierlin’s sign”—appears as a narrowing of the terminal
ileum with rapid empyting into a shortened, rigid, or obliter-
Enzyme-Linked Immunoassay Test ated caecum; and
A new test, Quantiferon (QFT-g), was approved in 2005 by the US Food
- “string sign”—a narrow stream of barium, indicating stenosis
and Drug Administration (FDA). The test basically detects the presence
Both Stierlin and String signs can also be seen in Crohn’s disease.
of interferon gamma release protein (IFN-g) from the blood of sensi-
Enteroclysis followed by a barium enema may be the best protocol for
tised patients when incubated with the early secretory antigenic target-6
evaluation of intestinal tuberculosis.
(ESAT6) and culture filtrate protein 10 (CFP10) peptides. The test is as
sensitive as, and more specific than, the tuberculin skin test and has been Ultrasonography
recommended as a screening tool for diagnosing disease as well as infec- Ultrasound is more helpful in peritoneal and nodal tuberculosis, but
tion. No available serodiagnostic test for TB has adequate sensitivity and it may also identify thickened and dilated bowel loops. The following
specificity for routine use in diagnosing TB in children. features may be seen:
Chest Radiograph • Free or loculated ascitis.
Evidence of tuberculosis in a chest radiograph supports the diagnosis, • “Club sandwich” or “sliced bread” sign, due to localised fluid
but a normal chest radiograph does not rule it out. It may show signs between radially oriented bowel loops.
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of active tuberculosis in 15% of patients. The findings can be (1)
miliary tuberculosis in a sick child without eosinophilia; (2) atelectasis, • Lymphadenopathy may be discrete or conglomerated (matted). The
emphysema, bronchiectasis, or parenchymal opacity—any of these echotexture is mixed heterogenous, in contrast to the homogenously
when present with pleural effusion or hilar lymphadenopathy indicates hypoechoic nodes of lymphoma. Both caseation and calcification
active disease; or (3) patchy consolidation or infiltration, which can are highly suggestive of a tubercular aetiology.
be nonspecific but when associated with a positive Mantoux test and • Bowel wall thickening—best appreciated in the ileocaecal region.
cavitation in the apex indicates activity. Signs of “old” tuberculosis
(e.g., obliterated costophrenic angle, calcified hilar lymph nodes, or a • Thickening of the small bowel mesentery of 15 mm or more.
fibro-calcific lesion) are present in 20% of patients. • Pseudo-kidney sign—involvement of the ileocaecal region that is
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Plain Radiograph Abdomen pulled up to a subhepatic position.
An erect radiograph is also invaluable at the time of abdominal pain Ultrasound-guided fine-needle aspiration (FNA) biopsy has been used
in demonstrating dilated jejunal and ileal loops with multiple air fluid successfully in the diagnosis of abdominal tuberculosis. Ultrasonography
levels, with an absence of gas in the colon and fixed bowel loop in may also be useful for guiding procedures such as ascitic tap and FNA
cases of obstruction, pneumoperitoneum in cases of perforation, and cytology or biopsy from the lymph nodes or hypertrophic lesions.