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Background
The perihepatic space is an important anatomic location for pathology. Knowledge of its normal anatomy can be helpful in identifying and understanding various pathological conditions that may occur in this space. The perihepatic space is composed of mainly the right subphrenic and subhepatic spaces. The liver is surrounded by the visceral peritoneum, which contains a small amount of serous fluid. The distribution and dynamics of the peritoneal fluid is influenced by the hydrostatic pressure and gravity in the context of peritoneal recesses and mesenteric reflections. These dynamics allow the spread of tumor or inflammatory processes to the perihepatic space. Liver pathologies can extend beyond the liver capsule into the perihepatic space. Other peritoneal and extraperitoneal pathologies may utilize the hepatic ligaments to communicate through the perihepatic space. Radiologists will be able to broaden their differential diagnosis for abdominal lesions with this understanding.

Educational Goals / Teaching Points
Review normal anatomy of the perihepatic space, outlining the peritoneal recesses and mesenteric reflections. Discuss the dynamics of the peritoneal fluid and how it influences the spread of pathology through the perihepatic space. Review CT and MRI for examples of benign and pathological findings involving the perihepatic space. Some discussed diagnoses will include lipoma of the Glisson’s capsule, benign mesenchymal lesion, dropped gallstones, pseudomyxoma peritonei, and endometriosis.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Anatomy of the perihepatic space will be delineated by a case of a patient with suspected peritoneal dialysis fluid leak. The case revealed a normal distribution without loculations of dialysis fluid mixed with Isouvue 240-water soluble contrast. Cases of dropped gallstones in the peritoneal cavity during a laparoscopic cholecystectomy will demonstrate the importance of identifying them. Complications involve abscess and fistula formation requiring gallstone removal. In addition, cases of Glisson’s capsule lipoma will be presented, which describes ectopic location of colonic epiploic fat within the liver capsule. Furthermore, cases of pseudomyxoma peritonei will detail a syndrome of progressive intraperitoneal mucinous ascites related to a mucin-producing neoplasm. Examples of endometriosis and benign mesenchymal lesions likely spread through the perihepatic space will be presented. Differential diagnoses for these various perihepatic space pathologies will be discussed.

Conclusion
Knowing normal anatomy of the perihepatic space as well as understanding the distribution and dynamics of the peritoneal fluid is important. This case-based review will help radiologists comprehend the pathophysiological process leading to the perihepatic space pathologies. It will help radiologists broaden the differential diagnosis for various abdominal lesions. This is important because with the increased utilization of cross-sectional imagining, more pathology is being identified in the perihepatic space with implications to patient management.