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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.
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