A 31-year-old man was admitted to our department in April 2009 with the history of right upper abdominal pain, fever, and bilious vomiting. In his medical history, there was a posttraumatic splenic hematoma in August 2007 which required splenectomy. No tuberculosis exposure was mentioned. Physical examination revealed a body temperature to 38  and a painful mass over the right flank region. Laboratory results revealed an increased erythrocyte sedimentation rate (120 mm/1 ) and C-reactive protein (80 mg/L) associated with leucocytosis (19000/mm3, 83% neutrophils, and 7% lymphocytes), mild anaemia (haemoglobin 11,2 g/dL), and thrombocytosis (platelets = 773000/UL). Liver function tests, blood urea nitrogen, and serum creatinin were within normal limits. A chest film was normal. 
An abdominal computed tomography revealed a large cystic retroperitoneal mass (184 x 126 mm) extending from the flank to right iliac fossa, pushing the right colon anteriorly, surrounding the anterior sides of the abdominal aorta and the inferior vena cava. It is located behind duodenum, ahead the kidney and under the liver, without signs of invasion and without lymph node involvement. The lesion had spontaneous density between 12 and 30 Hounsfield units. There was a complete enhancement of the lesion (Figure 1).
An MR scan revealed a cystic mass, hypointense in T1, and hyperintense in T2 with an enhancement of the entire lesion (Figure 2).
Percutaneous aspiration of the mass, under sonographic guidance, yielded mucinous fluid but insufficient for mycobacteriological examination. Blood cultures for aerobic and anaerobic bacteria did not produce any growth. 
Thus, a laparotomy was performed. It revealed a large retroperitoneal yellowish mass containing pus. It is extending from the root of the mesentery to the vena cava. The access to this mass is difficult, and it required dividing the coloepiploic attachments. There were no carcinosis or ascits. The small bowel and the appendix were normal. 
The histopathological examination showed epitheloid granulomas with necrosis, giant cells, and lymphoepitheloid infiltrate (Figure 3). Culture and polymerase chain reaction of tuberculosis using the surgical specimen were not performed. The diagnosis of retroperitoneal tuberculosis was established. There were not other tuberculosis involvements: computed tomography chest was normal, and MR scan of the spine excluded a spondylodiscitis. HIV test was negative.
Antitubercular therapy was started with isoniazid (300 mg once daily), rifampicin (600 mg once daily), pyrazinamide (2000 mg once daily) and ethambutol (1200 mg once daily), and was given for 9 months. No others antibiotics were administrated. The cyst gradually subsided and disappeared with a normal abdominal computed tomography 6 and 12 months later.