Abstract
During a period of eight years (1999–2006), 92 cases of abdominal TB were diagnosed by fine needle aspiration cytology (FNAC). Based on our findings, FNAC is a simple, fast, accurate and inexpensive diagnostic procedure for cases of suspected abdominal TB.
Introduction
Despite the rapid progress in chemoprophylaxis and therapy, abdominal TB continues to be a health problem in developing countries such as India where it constitutes 1% of all hospital admissions.1,2 A confirmed diagnosis of abdominal TB is important, as the early institution of chemotherapy can achieve satisfactory results and prevent the development of complications which may require surgery. The aim of the present study was to evaluate the usefulness of ultrasoundguided fine needle aspiration cytology (FNAC) in the diagnosis of abdominal TB.
Materials and methods
Over a period of eight years (1999–2006), 92 cases of abdominal TB were diagnosed by FNAC. Lymph nodes were most commonly involved (65%) followed by bowel (13%), liver (6.5%), spleen (8.6%), pancreas (2.2%) and tubo-ovarian masses (4.4%).
All the aspirations were performed under ultrasound guidance as a first line investigation for most patients. The diagnosis of abdominal TB/granulomatous inflammation was rendered when one or more of the following cytological features were present.
Eosinophilic granular caseous material; Caseation necrosis and epithelioid cell granulomas with/without giant cells; Epithelioid cell granulomas with/without giant cells and without caseation necrosis; And/or presence of acid-fast bacillus (AFB) on a Ziehl-Neelsen stain.
Results
The age of the patients ranged from 7 to 68 years, with the majority in the third decade. There were 45 males and 47 females. The clinical and radiological diagnosis prior to aspiration was TB in 43 cases. Fifty presented with a palpable abdominal mass. In remaining cases, the size of mass ranged from 2–5 cm in diameter on ultrasonography or computerized tomography examination.
Cytological findings
The aspirate consisted of cheesy or necrotic material in 27% of patients, pus-like in 30% and tissue particles mixed with blood in 43% (Table 1).
The correlation between the gross appearance of aspirate and the microscopic features of smears in 92 cases of abdominal TB
Lymph node
Para-aortic lymph nodes were most commonly involved (70%) followed by porta hepatis (12%), mesenteric (10%) and pelvic lymphnodes (8%). Forty-five (75%) showed the presence of epithelioid cell granulomas (Figure 1) while necrosis was observed in 60%. AFB positivity was seen in 32 of 60 cases (53%). Two were HIV-positive; the smears showed necrosis and the AFB was highly positive. The AFB culture in one of these cases showed atypical mycobacteria.
A photomicrograph showing epithelioid cell granuloma in a case of mesenteric lymphnode TB. The background shows lymphocytes and necrosis. (MGG, ×400)
Bowel
There were 12 cases of bowel wall involvement. The ileocaecal region was most commonly involved (75%), the small intestine (9%) and a thickened ascending colon (16%). A coexistent lymph node involvement was seen in seven cases (60%) and two (16%) showed coexistent splenomegaly. Granulomas were seen in all the cases but necrosis was seen in only one who was AFB positive.
Liver
The liver was involved in six cases, five of whom had granulomatous hepatitis and one had TB. The ultrasonography examination revealed diffuse heterogeneous echotexture without any well-defined mass in four cases, focal lesions in two and suspected abscess in one. All revealed epithelioid cell granulomas admixed with benign hepatocytes and ductal cells. Necrosis and AFB was seen in one patient who was diagnosed as having TB.
Spleen
Splenic TB was diagnosed in eight cases: one was HIV-positive. Splenomegaly was present in six with a splenic enlargement of 4–9 cm below the left costal margin. In four, ultrasonography showed focal splenic lesions. Coexistent lymph node involvement was seen in five case and hepatomegaly in two. Five revealed epithelioid cell granulomas along with giant cells but necrosis was seen in three. AFB positivity was seen in 80%.
Pancreas
There were two cases of pancreatic TB. Both were suspected to be malignant with focal mass lesions measuring 3 cm and 4 cm in the head of the reas. Epithelioid cell granulomas with Langhans and foreign body giant cells were also noted, although the AFB was negative in both the cases. Both the patients responded well to anti TB chemotherapy.
Tubo-ovarian masses
A diagnosis of TB was made in four cases; granulomas in two; necrosis along with acute inflammatory cells were seen in two; and AFB positivity in two.
Discussion
Abdominal TB continues to be a diagnostic challenge for the clinician because of its non-specific and protean manifestations.1,2
Lymphadenopathy is the most frequent finding on imaging in patients with abdominal TB. 3 Although CT scanning has been said to be the most preferred modality for guidance in diagnosing abdominal TB, 4 recent studies have shown that ultrasonography can be safely used to aspirate small pelvic and abdominal lymph nodes. 5
Though granulomatous hepatitis with diffuse involvement of the liver has been reported, localized involvement of liver and spleen producing macronodules was uncommon in our study.6–8 There was a single case of hepatic abscess which was AFB positive. In others the FNAC could not demonstrate caseation or AFB positivity. Thus, the cytological findings of a granuloma in a liver aspirate need to be correlated clinically.
A review of the literature has revealed only the occasional case report describing the use of splenic FNAC in the diagnosis of TB. 8 In the majority of cases, splenic TB is diagnosed either by laparotomy or by aspiration from alternative sites.7,8
The yield of aspirated material and AFB positivity is disappointingly low in cases of bowel FNAC. The low yield can be explained by presence of desmoplastic response secondary to chronic hypertrophic lesions. 6
The isolated pancreatic TB seen in our patients, without involvement of lymphnodes or other organs, is rare. 9 Thus, TB should be borne in mind for the differential diagnosis of pancreatic masses in the patients coming from areas where TB is endemic.
The aspirated material may contain necrotic material with or without granulomas and giant cells. It is necessary to test the AFB in such cases in order to make a definitive diagnosis of TB. However, failure to demonstrate AFB does not exclude TB as, for bacilli to be demonstrated microscopically, there must be 10,000–10,0000/ mL of material. 6
In a suspected case of abdominal TB, a battery of tests is usually carried out in order to reach a diagnosis. The biopsy is invasive, laborious and time consuming.5,10 In contrast to these tests, ultrasonic-guided FNAC is a safe, reliable and accurate method for testing suspected cases of abdominal TB. In a minority of patients, i.e. those with negative cytological findings and where there is a strong clinical suspicion of TB, the aspirated material may be used for other tests such as polymerase chain reaction, immunofluorescent staining or newer culture methods.