Teaching Case

A 27-year-old fit and well Caucasian man presented with a 3-days history of fever, abdominal pain and diarrhoea following a holiday in Ibiza. He presented as an emergency 2 days after visiting his general practitioner. Abdomen was tense and distended. Biochemistry showed low WCC (lymphocytopenia), CRP 300 mg/L. Malaria parasitology, Hepatitis/HIV serology were negative.

Fig 1: Abdominal radiograph showing dilated bowel loops

Fig 2: CT Findings:
• Large volume intra-abdominal and pelvic ascites
• Distended small and large loops of bowel
• Mild thickening of mid sigmoid colon
• Omental thickening and stranding
• No free gas or abdomino-pelvic lymphadenopathy

Background:

The most common site for extra-pulmonary tuberculosis (TB) is the abdomen with peritoneal disease being the commonest form [1]. Extra-pulmonary TB accounts for 15% of cases worldwide and has proven to be both a clinical and bacteriological diagnostic challenge [2, 7]. A high index of suspicion should be maintained in patients presenting with unexplained ascites [5].

Ascites may be the sole presenting sign for peritoneal TB [4, 6]. The presence of malignant ascites should raise the suspicion of peritoneal carcinomatosis [4] as a first-line differential diagnosis. Other differentials include: metastatic disease, TB peritonitis as well as nephrotic syndrome. Omental appearance may be cake-like or nodular and is similar to peritoneal carcinomatosis [1] which forms the main differential diagnosis.

Abdominal TB can involve solid organs, lymph nodes and the gastro-intestinal tract [3].
There are 3 types of tuberculous peritonitis [1, 6]:

1. Wet type - 2. Dry type - 3. Fibrotic-fixed type

In cases of TB peritonitis, the CT findings would include: ascites, nodular or symmetrical thickening of the peritoneum and mesentery, abnormal peritoneal or mesenteric enhancement and low attenuating lymphadenopathy. In addition, there may be type-specific findings or that of a mixed-picture. The wet type has a high attenuation (HU 20-45) ascites due to high protein and cellular content [2, 4]. The dry type presents with a thickened ‘cake-like’ omentum and mesenteric lymphadenopathy. Omental caking with fixed bowel loops, matted loops and mesentery and loculated ascites is seen in the fibrotic-fixed type [4-7].

Clinical Perspective:
Atypical presentation of abdominal ascites, no weight loss or loss of appetite. Fever of unknown origin and abdominal pain/distension were the main manifestations.

Imaging Perspective:
Justified by the abnormal abdominal radiograph, a CT scan of the abdomen and pelvis was subsequently performed (portovenous phase). That showed several interesting findings including: large volume ascites, omental thickening (Fig. 3: yellow arrow-heads) and bi-basal lung atelectasis. Direct visualisation of the distal large bowel was also recommended due to mild mid-sigmoid colonic thickening (Fig. 3: red arrows). The cause of this, however, was not demonstrable on the study. The subsequent flexible sigmoidoscopy was normal.

An ultrasound-guided ascitic drain was inserted and fluid samples sent for microbiology culture and cytology. Finally, the ascitic fluid was positive for Mycobacterium tuberculosis.

Learning Points:
1. In patients presenting with lymphocytic ascites, TB peritonitis should be considered.
2. Increasing utilisation of ultrasound & computed tomographic scan for the diagnosis and as a guidance to obtain peritoneal biopsies/ aspirations.