If the gas leak is small and the perforation in the GI tract is well localized, there will not be any frank perforation. The hyperechoic collection of gas with its characteristic reverberation echoes is truly local and will not shift on patient repositioning. Most of the localized hyperechoic collections of gas will be seen in the immediate vicinity of the GI tract and will be difficult to differentiate from the intraluminal gas collections (Fig. 8.41). Apart from the intracavitary hyperechoic structures of the perforation, there may be fluid as well (mixed with hypoechoic regions), resulting in a mixed image.

Fig. 8.41

a Localized hyperechoic structure with reverberation echoes and posterior shadowing around the hepatic portal (subhepatic left) in a localized perforated duodenal ulcer.

b Hyperechoic structures in localized perforation.

Gas Abscess

In a gas abscess the hypoechoic regions of the liquid components may be predominant. The gas produced by the bacteria is characterized by individual marked echo complexes increasing over the course of the abscess (Fig. 8.42). In most cases it displays an irregular margin. Differential diagnosis is based on the clinical picture supplemented by fine-needle puncture.

Fig. 8.42 Localized hypoechoic, rather smoothly defined structure with a hyperechoic region corresponding with gas; the “curtain-like” appearance and the posterior shadowing are indicative. Large paracolic gas abscess on the right complicating necrotizing pancreatitis.

■ Wall Structures

Smooth Margin

Right-sided Heart Failure

Cirrhosis

Peritoneal Carcinomatosis

Peritoneal Carcinomatosis

In peritoneal carcinomatosis the peritoneum may still be smoothly delineated and appear absolutely normal (Figs. 8.17, Fig. 8.18). However, much more common are irregularities, septation, and tumor nodes on the peritoneum itself. The findings are considered as cardinal signs of malignancy.

Irregular Margin

Pancreatitis

Peritonitis

Peritoneal Carcinomatosis

The intra-abdominal collection of fluid in pancreatitis is characterized not only by its internal echoes but, as has already been stated above, quite often by septation and strands of fibrin. These originate from the peritoneum and will lead to an irregular outline. “Fluttering fibrin strands” originating from the peritoneum may be found in pancreatitis as well as peritonitis or after a bleeding has occurred (Fig. 8.44,

Fig. 8.45).

Fig. 8.44 “Flags” of fibrin coating the peritoneum and dominating the picture in necrotizing pancreatitis (exudate).

Fig. 8.45 The septation may become almost complete and can mask all of the peritoneum. Honeycomb texture due to strands of fibrin in necrotizing pancreatitis.

The importance of ultrasound-guided fineneedle puncture in the precise assessment of the fluid has already been discussed. In malignant ascites this is an exudate that quite often has high cholesterol levels. Malignant cells will be found in 50–70% of cases. Repeat paracentesis and cytological evaluation will increase the sensitivity to 70–80%.7

Table 8.5 Primary malignancies in peritoneal carcinomatosis

Table 8.6 Signs of peritoneal carcinomatosis2