Discussion
Tuberculosis (TB) is a multisystemic infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Although pulmonary TB is the most common presentation of disease; extrapulmonary TB (EPTB) accounts for nearly 20 percent of all cases of TB in immunocompetent hosts, and Tuberculosis (TB) of the abdomen is seen in 12% of patients with miliary TB (5)(6).By definition, EPTB describes the occurrence of TB at sites other than the lung. EPTB can occur in almost any organ system, with the most common sites of infection being the lymph nodes, pleura, genitourinary system, and bone (5)(7). Abdominal TB is the sixth most common site for EPTB, and includes infection anywhere in the gastrointestinal tract, peritoneum, and intra-abdominal organs such as the spleen, liver, and pancreas (7).
The clinical presentation of abdominal TB especially pancreatic and hepatobiliary involvement is often insidious, with nonspecific constitutional symptoms occurring frequently (5). In a study by Saluja et al. , the three most common presenting complaints in patients found to have pancreatic TB were abdominal pain, jaundice, and weight loss (8). Individuals infected with pancreatic TB may also present with fever, gastrointestinal hemorrhage secondary to splenic vein thrombosis, and anorexia (8). If pancreatic TB is suspected, preliminary testing such as tuberculin skin testing and an interferon-γ  release assay for TB may be negative in patients. Sharma et al. suggest that the sensitivity of tuberculin skin testing in patients with abdominal tuberculosis may range from 58 to 100 percent (5). With the wide-ranging sensitivities of TB screening modalities and an often nonspecific and varied clinical presentation of pancreatic and hepatobiliary TB, diagnosis of infection relies heavily on radiologic and histopathologic findings. In our case, the patient presented with abdominal pain mainly epigastric associated with jaundice and weight loss. His interferon-γ  release assay for TB (Quantiferon TB Gold) was positive from the beginning.
Ultrasonography or computed tomography (CT) are often first-line diagnostic modalities in patients presenting with signs of pancreatic pathology (2)(5). Ultrasound is often the first investigation used for diagnosis of pancreatic tuberculosis which may reveal a focal hypoechoic mass or cystic lesion of the pancreas mostly situated in the head and uncinate process of the pancreas (2).
CT scan is still regarded as the investigation of choice for pancreatic pathology (9).CT scan may show hypodense lesion with irregular border in the head of the pancreas, diffuse enlargement of the pancreas, or enlarged peripancreatic lymph nodes (9). The presence of hypodense peripancreatic lymph nodes with rim enhancement, ascites, and/or mural thickening affecting the ileo-caecal region suggests the pancreatic tuberculosis (9). Magnetic resonance imaging (MRI) findings of focal pancreatic tuberculosis include a sharply delineated mass in the pancreatic head showing heterogeneous enhancement which is hypointense on fat-suppressed T1-weighted images and shows a mixture of hypo- and hyperintensity on T2-weighted images (10). In our case, his US showed a hetero echoic cystic lesion in the pancreatic head, and the CT showed Pancreatic parenchyma had diffused stranding and hyperechogenic foci, lastly his MRI showed a relatively well-defined lobulated heterogeneous T2 hyperintense necrotic lesion involving the pancreatic head and the caudate lobe of the liver. Techniques for pancreatic biopsy include CT or ultrasound-guided percutaneous biopsy, surgical biopsy, or endoscopic ultrasound (EUS) guided fine-needle aspiration (FNA)(2). The American Joint Commission on Cancer (AJCC) recommends EUS-FNA as the diagnostic modality of choice in patients with pancreatic masses and has found it to be the most sensitive and specific method for identifying the etiology of pancreatic masses (2). The presence of on-site cytology is imperative in the diagnosis of pancreatic TB, as the immediate interpretation of the specimen will allow clinicians to request appropriate cultures (2). Acid-fast bacilli are commonly not seen with FNA. In a study by Farar et al., nearly 40 percent of patients with abdominal TB had staining that was negative for acid-fast bacilli (11). Clinicians should be cognizant of the relatively low yield of FNA specimens to reveal acid-fast bacilli and thus culture the specimen for evidence of Mycobacterium tuberculosis  (11).In our experience, the patient underwent EUS-FNA to confirm the diagnosis and for sample collection, his AFP smear and PCR came positive for acid-fast bacilli (Mycobacterium tuberculosis) .
Once the diagnosis of abdominal TB has been made, standard anti-TB therapy appears to be successful in the management of this infection. A minimum of 6 months of anti-TB therapy is often indicated to achieve resolution of pancreatic lesions and alleviation of symptoms. Follow-up CT imaging after treatment may reveal the complete resolution of pancreatic lesions secondary to tuberculosis and may guide clinicians regarding the duration of therapy (12).