Morison’s pouch is also known as the posterior right subhepatic space or hepatorenal fossa. It separates the liver from the right kidney and is not filled with any fluid under normal conditions. It is a potential space, meaning a space that can occur between two adjacent structures that are normally pressed together. The anterior boundary consists of the right hepatic lobe and gallbladder.

Posteriorly, there is the right kidney, right adrenal gland, the second part of the duodenum, hepatic flexure, and pancreatic head. The transverse mesocolon lies inferiorly. The posterior right subhepatic space communicates with the right subphrenic space and right paracolic gutter.

Liver relations to other organs.

Available at: https://docnesia.com/wp-content/uploads/2018/09/02c29f44a8f060d36e027f2830159e1fde59368c.png (Accessed: 7 March 2020).

Probe position in assessment of hepatorenal recess – Morison's pouch PAME Maribor
Ultrasound image of Morison's pouch PAME Maribor

Available at: https://www.stepwards.com/?page_id=1275 (Accessed: 7 March 2020).

Fluid can collect in this space in different circumstances, such as ascites or hemoperitoneum. This fluid may be seen as an anechogenic border between the liver and the kidney on the ultrasound. If there has been recent trauma or bleeding in the abdomen, it can often be discovered in this location. Free fluid in the pouch other than bleeding is known as ascites. It can commonly be caused by heart, liver, or kidney conditions. Early visualization of fluid in the hepatorenal recess on the FAST scan may be an indication for urgent laparotomy.

Free fluid in Morison’s pouch PAME Maribor

Ultrasound examination

FAST: Right upper quadrant – perihepatic window

The liver, right kidney, and Morrison’s pouch are assessed in this view. A transducer is put in the mid-axillary line at the lever of the 10th rib, with the marker on the probe pointing towards the patient’s head. Ideally, the kidney, liver, and diaphragm are seen at the same time. The hepatorenal recess should be placed in the center of the ultrasound screen. At this point, the probe is tilted around to assess Morrison’s pouch, liver, and kidney. It may be necessary to move one intercostal space inferiorly to evaluate the liver tip. Ribs may get in the way of a clear picture. In this case, the probe can be rotated around its axis, with the marker pointing slightly posteriorly (to get in between the ribs). Another way to avoid rib shadows is to ask the patient to inhale.

The examination: https://youtu.be/0VTRm_DNW8s

FAST positive Morison’s pouch PAME Maribor

FAST positive Morison’s pouch with cholecystitis PAME Maribor

In a healthy patient, the liver and kidney are close together, with no hypoechogenic space in between. There is a hyperechogenic line (the diaphragm) on the left of the ultrasound picture. Morrison’s pouch (hepatorenal recess – the space between the liver and kidney) is the deepest space in a supine patient. Fluid accumulates there because of gravitation. However, as it is the deepest space, fluid may not have already reached this space. Therefore, the inferior tip of the liver must always be obtained, as fluid may collect there prior to Morrison’s pouch. Even a small collection of fluid is “FAST positive.”

When abdominal organs and spaces are evaluated, the probe is slid cranially to assess the thorax for any possible fluid. The diaphragm (hyperechogenic line left to the liver) is placed in the center of the screen.

Ascites

Ascites refers to fluid buildup in the peritoneal cavity. This fluid can also leak into Morison’s pouch, causing it to expand. The main symptom of ascites is visible abdominal swelling. Other potential symptoms include reduced appetite, pain, or pressure in the abdomen, abdominal tenderness, and breathing problems.

Ascites is most commonly caused by cirrhosis (85%), cancer (10%), and heart failure. The mechanism by which ascites develops in cirrhosis is multifactorial. Severe sinusoidal portal hypertension and hepatic insufficiency are the initial factors. They lead to a circulatory dysfunction characterized by arterial vasodilation, arterial hypotension, high cardiac output, hypervolemia, and renal sodium and water retention. The arterial vasodilation of splanchnic circulation occurs because of the increased production of local vasodilators. The vascular resistance remains normal in the surrounding organs (kidney, muscle, and skin). A very high flow into the splanchnic microcirculation causes increasing hydrostatic pressure. Consequently, more lymph is produced than reabsorbed. The lymph leakage from the liver and other splanchnic organs leads to fluid accumulation in the abdominal cavity.

Ascites with floating intestine PAME Maribor

Hemoperitoneum

Hemoperitoneum refers to built-up blood in the peritoneal cavity, which can also get into Morrison’s pouch. It can cause a wide range of symptoms, including abdominal pain or tenderness, general weakness, paleness, and loss of consciousness. It is caused by an injury to a nearby blood vessel, which can be a product of abdominal injuries, abdominal aneurysm ruptures, liver damage, complication of fluid drainage from the abdomen, or ectopic pregnancy. Hemoperitoneum is considered an emergency.

When assessing the type of fluid, we have to keep in mind that simple ascites is anechogenic, whereas exudative, hemorrhagic, or neoplastic ascites contain floating debris.

Resources

Arroyo, V. (2002) ‘Pathophysiology, diagnosis and treatment of ascites in cirrhosis.’, Annals of hepatology : official journal of the Mexican Association of Hepatology, pp. 72–79. doi: 10.1016/s1665-2681(19)32178-7.

Ascites | Radiology Reference Article | Radiopaedia.org. Available at: https://radiopaedia.org/articles/ascites (Accessed: 7 March 2020).

Smereczyński, A., Kołaczyk, K. and Bernatowicz, E. (2017) ‘Difficulties in differentiating the nature of ascites based on ultrasound imaging’, Journal of Ultrasonography. Medical Communications Sp. z.o.o., 17(69), pp. 96–100. doi: 10.15557/jou.2017.0013.

Moore, C. M. and Van Thiel, D. H. (2013) ‘Cirrhotic ascites review: Pathophysiology, diagnosis and management’, World Journal of Hepatology. Baishideng Publishing Group Inc, pp. 251–263. doi: 10.4254/wjh.v5.i5.251.