To illustrate the wide range of diagnostic possibilities in patients with fever and right hypochondrium pain, a retrospective analysis of 123 cases of patients with these symptoms admitted in our institution from May to October 2019 was performed. They were firstly evaluated by an urgent abdominal US examination and several different diagnoses were made (Fig. 4).
Acute cholangitis
An US examination is mandatory to evaluate the bile ducts if this entity is suspected. The main radiological findings are intrahepatic and/or extrahepatic bile duct dilatation (over 2 mm and 7 mm respectively), presence of calculi and/or bile sludge into the biliary tree and duct wall thickening. Small liver abscesses may be observed in US when the infection is advanced (Fig. 5).
Liver abscess
The most common cause is a local infection at biliary structures-AC or acute cholangitis (Fig. 5)- or a surgical procedure of the biliary tract (Fig. 6). Hematogenous dissemination is possible too from another digestive structures through porta vein –e.g. acute appendicitis, diverticulitis (Fig. 7)- or from other distant infections (Fig. 8).
US is the first imaging examination to be peformed if liver abscess is suspected. It shows a well-defined mass with mixed echogenicity because of blood and purulent content. Air-fluid levels can be present as a result of bacterial metabolism and it is seen as irregular echogenic lines in the upper portion of the lesion with acoustic shadowing artifact. Sometimes its appearance is cystic and demonstrates thick septa. In early stages, a phlegmonous abscess may be identified as a hypoechogenic ill-defined area oftenly difficult to be differentiated from normal hepatic parenchyma (Fig. 9). Doppler US and CEUS show the absence of vessels in the center of the lesion, which allows to differentiate it from other liver lesions.
Acute appendicitis
In US exams, appendicitis is diagnosed if the appendix is distended over 6 mm from outer to the outer wall and non-compressible by pressing the appendix with the transducer (Fig. 11).
Identification of an echogenic round structure with posterior shadow -appendicolith- also is considered a diagnostic sign of acute appendicitis. Peri-appendiceal free fluid may be present as a nonspecific sign as well as hyperechogenicity of adjacent fat tissue. The appendiceal wall can present hyperemia in Doppler color mode and in CEUS. Lack of wall layer differentiation may indicate impending gangrene or perforation.
Right colonic diverticulitis
Most frequently located in left colon, acute diverticulitis may affect the right side including the hepatic flexure and the first portion of the transverse colon. This situation constitutes a diagnostic challenge as it can be confounded with other right upper quadrant diseases. Sonography may approach the diagnosis by demonstrating inflammatory signs in affected segment of the colon such as concentric wall thickening, adjacent fat stranding and free fluid (Fig. 11). These findings are as well as present in intestinal graft versus host disease and neutropenic colitis (Fig. 12 & 13).
Acute pyelonephritis
Some US signs of acute pyelonephritis that are occasionally present include wall thickening of the urothelium, increase in kidney size or presence of perirenal fluid. However, B-mode images most commonly show no significant abnormality so it becomes important to detect possible changes in renal vascularization. Doppler US and specially CEUS are able to identify areas of decreased vascularization as a result of edema and ischemia in the renal parenchyma (Fig. 14). Involved areas can be cuneiform in shape due to the small vessel disposition. The term nephronia refers to a focal acute nephritis involving one delimited area, which should not be confused with a kidney abscess (Fig. 15).
Kidney abscess
The main role of sonography in pyelonephritis evaluation is to identify complications in patients at risk: diabetics, immunosuppression, an ineffective antibiotherapy or renal failure. This technique can reveal US signs of abscess in the renal parenchyma or in the perirenal fat. US findings are similar to liver abscess but in challenging cases, CEUS may help to differentiate them from renal masses or nephronias (Fig. 16).
Right basal consolidation
The involved parenchyma can present lower or similar echogenicity when compared to the liver. Hyperechogenic lines or balloon-like images are oftenly visualized and represent air bronchogram and alveologram respectively as a result of air entrapment (Fig. 17).