In literature, superior mesenteric artery (SMA) angle, also named as aortomesenteric angle (AMA), varies greatly in both adult and children; while the aortomesenteric distance also ranges widely. Both AMA and AMD are influenced by retroperitoneal fat. Decrease of AMA and AMD may lead to the superior mesenteric artery syndrome(SMAS), which is a rare medical condition mainly presenting with duodenum obstruction. To our knowledge, normal range of AMA and AMD in local young Chinese population remain unclear; on the other hand, there have only a few studies exploring the relationship between them. This project proposes to establish the normal range of AMA and AMD in local young Chinese population, and to further investigate how the retroperitoneal adipose tissue correlates with AMA and AMD. The normal range obtained in this proposed study will provide more specific reference value to distinguish abnormal AMA and AMD, and to improve the diagnosis accuracy of SMAS in local population. Moreover, this study will provide deeper insight concerning the impact of retroperitoneal fat on AMA and AMD.

Inclusion Criteria:

• With age range of 10-35 years old.
• Chinese ethnicity.
• With abdomen contrast CT.

Exclusion Criteria:

• Any patients with diagnosis of SMAS will be excluded from the Non-SMAS group.
• Patients who had undergone more than one CT scan during the research period.
• Previous retroperitoneal, abdominal surgery.
• Conditions causing significant weight loss, e.g. anorexia nervosa, malabsorption.
• Presence of abdominal masses or pathology that will affect the anatomy of aorta- superior mesenteric artery and the retroperitoneal structures.
• Presence of severe scoliosis and/or history of spinal fixation that may increase incidence of SMA syndrome.
• Presence of free intraperitoneal or retroperitoneal fluid that may affect fat measurement, e.g. following trauma, or ascites.

The investigators will retrospectively recruit individuals from the local population who had undergone abdomen contrast CT scans within hospitals in the New Territories East Cluster (NTEC) of Hong Kong for both emergency and elective purposes in the year 2013-2019. Total sample will comprise two groups: (1) Non-SMAS Group (N=500); and (2) SMAS group (N=10).