Teaching Case

A 50-year-old male presented three months ago with right upper quadrant abdominal pain, fever, and malaise lasting two weeks. Physical examination showed tenderness in the right upper quadrant. Laboratory tests indicated elevated liver enzymes and leucocytosis, leading to a referral to the radiology department for further evaluation.

A CT scan was performed with spiral axial sections from the level of the diaphragm to the lower abdomen using oral contrast. Findings include two peripherally enhancing hypodense lesions with shaggy margins and minimal perilesional oedema in the right lobe (segment VII) and left lobe (segment IVb) of the liver. The right lobe lesion measures 23 x 20 x 22 mm (AP×TR×CC), while the left lobe lesion measures 13 x 15 x 17 mm (Figures 2a, 2b, 2c and 2d). Also, a 47 × 60 × 55 mm (AP×TR×CC) well-defined, oval, hypodense lesion with central chunky calcifications in the hypogastric region of the mesentery was detected. This lesion abuts small bowel loops, the mesorectal fascia, the left external iliac vessels, the psoas muscle (with preserved fat planes), and posteriorly focally abuts the ureter with loss of fat plane, with no significant enhancement noted on post-contrast imaging (Figures 1a, 1b, 1c, 1d and 3).

Background

Loose peritoneal bodies, also known as “peritoneal mice”, are rare, benign entities typically discovered incidentally on imaging. They arise from infarcted and calcified epiploic appendages that detach and float freely in the peritoneal cavity [1]. These bodies are usually small, but in rare cases, “giant” loose bodies, defined as measuring over 50 mm, have been reported [2]. In this case, the loose peritoneal body measured approximately 60 mm (TR axis). These bodies are generally asymptomatic and are found during imaging for unrelated conditions.

Clinical Perspective

This case involves a 50-year-old male who initially presented with a liver abscess, successfully treated with aspiration. At follow-up, the patient was asymptomatic, but a giant loose peritoneal body was incidentally discovered. Though typically benign, larger peritoneal bodies, such as the 60 mm mass seen here, may raise concerns for complications like bowel obstruction, though such occurrences are rare [3]. However, the incidental nature of this finding emphasises the importance of recognising benign pathology to avoid unnecessary intervention.

Imaging Perspective and Differential Diagnosis

On CT, loose peritoneal bodies appear as well-circumscribed, mobile, calcified masses. The smooth, round shape and central calcification pattern help differentiate them from other calcified entities, such as calcified lymph nodes, ectopic gallstones, peritoneal metastases, omental infarctions, or foreign bodies.

• Calcified mesenteric lymph node: These nodes can calcify following infections or inflammatory conditions such as tuberculosis or sarcoidosis. They are usually present as round, dense structures without significant surrounding inflammation and often reflect a history of chronic infection or inflammation.
• Gallstone in the peritoneal cavity: Gallstones may become ectopically located in the peritoneal cavity, especially after a cholecystectomy, where spillage of gallstones can occur. Such ectopic gallstones may calcify over time. If a history of cholecystectomy is present, these calcifications might be found in the upper abdomen near the liver.
• Peritoneal metastasis: Calcified peritoneal metastases can be found in mucinous adenocarcinomas, particularly from gastrointestinal or ovarian origins. These lesions may present as irregular, enhancing calcified nodules and are often accompanied by other signs of malignancy, such as ascites or additional metastatic nodules.
• Omental infarction: These are rare and typically associated with focal abdominal pain. If chronic, infarcted omental tissue may calcify, forming irregular, encapsulated masses. Acute presentations often show fat stranding and localised pain, whereas a chronic infarct may be incidental with calcification on imaging.
• Foreign body: Retained surgical materials or other foreign bodies in the peritoneum can calcify over time. Radiopaque foreign bodies, such as surgical sponges, may have characteristic appearances based on their composition. A history of previous abdominal surgery would be relevant in considering this differential.

In our case, the imaging showed a smooth, round, mobile calcified mass with no signs of enhancement or surrounding inflammation, consistent with a benign loose peritoneal body. The absence of other concerning features allowed for a confident diagnosis without further diagnostic steps.

Outcome

Since the patient was asymptomatic, no treatment was required for the loose peritoneal body. Conservative management, including regular follow-up without intervention, is the preferred approach unless complications arise, which is uncommon [4].

Take Home Message / Teaching Points:

• Loose peritoneal bodies are rare, typically benign entities discovered incidentally during imaging.
• Recognising their typical CT features, such as smooth calcifications and free mobility, is essential to prevent unnecessary diagnostic or surgical interventions.
• Conservative management is appropriate in asymptomatic patients, even for larger peritoneal bodies like the one in this case.

All patient data has been completely anonymised throughout the entire manuscript and related files.