Clinical case: Subhepatic cecum with subhepatic appendicitis

Objectives

• Describe the meaning and boundaries of the abdominal quadrants and regions.
• Describe the location and significance of the hepatorenal pouch of Morison. 
• Explain why the results of the ultrasound exam were nonspecific, what was the significance of the absence of free air under the diaphragm, and why the preliminary diagnosis was a peptic ulcer.
• Describe the etiology of appendicitis and what “guarding” means.
• Describe the etiology of GI anomalies relative to incomplete (malrotation) and fixation.

Abdominal regions and quadrants

For descriptive purposes the abdominal wall and the contents of the abdomen have classically been divided into quadrants (Figure 5), but for more accurate description into nine regions (Figure 5). The midsagittal plane and a horizontal plane through the umbilicus divide the abdomen into quadrants; in contrast the midaxillary, and subcostal (10th costal cartilage) and intertubercular planes are used to define the nine abdominal regions.

Hepatorenal recess (pouch of Morison)

The hepatorenal recess (subhepatic recess, pouch of Morison or Morison's pouch; Figure 6) is a potential space that lies between the liver and right kidney. Normally the space is empty but fluid can collect in this space in circumstances where there is excess fluid (e.g., blood from trauma or infected fluids from an inflamed viscus) in the peritoneal cavity. This fluid may be visualized in ultrasound or CT). The presence of infected fluids in the hepatorenal pouch is potentially life-threatening because these fluids can result in peritonitis and sepsis.

Diferential diagnostics to perforated peptic ulcer

The patient, in this case, had pain in his epigastric and right hypochondriac regions (Figure 5), and dyspepsia. These two signs and symptoms plus fluid in Morison’s pouch suggest he had a perforated stomach or duodenal ulcer in which infected fluid from the ulcer was accumulating in the pouch. A positive finding of fluid in Morison’s pouch is sensitive for an abnormality but not specific for what the abnormality is. Furthermore, a perforated peptic ulcer also typically releases air that shows up as free air under the diaphragm in a chest radiograph and it is significant that this was not the case in this patient. In this case, the fluid in Morison’s pouch originated from the inflammation of appendix, which is a very rare location for that organ. Therefore, appendicitis was presented with signs and symptoms more frequently related with a perforated peptic ulcer. However, the opposite is possible too. In other cases the fluid from a perforated peptic ulcer may go down with gravity and cause inflammation of other parts of the parietal peritoneum. If this happens in the lower right quadrant, a perforated peptic ulcer may be misdiagnosed as acute appendicitis due to the location of the pain.

Etiology of appendicitis & guarding

The appendix is a tubular blind pouch that is attached to the cecum at the junction of the three taenia coli. Typically it is located in the lower right quadrant, or the right lumbar region (Figures 7&8).

The literal translation of 'appendix vermiformis' would mean that it is a worm-like structure. Let's take a closer look into it again.

When inflamed, the patient has appendicitis. Inflammation is often caused by a fecalith (small piece of fecal matter) obstructing fluid drainage from the appendix. The location of the base of the appendix typically corresponds tot McBurney’s point on the abdominal wall, which is two-thirds of the distance between the umbilicus and the anterior superior iliac spine. Usually, pain from an inflamed appendix migrates from the umbilical region to the right iliac (inguinal) regions. This occurs as the inflamed appendix swells and makes contact with the peritoneum on the anterior abdominal wall. The initial pain in the epigastric region, which is from a visceral source, is a good example of referred pain. The pathology is in the appendix, which is located in the lower right quadrant, but the pain is felt at the anterior abdominal wall in the epigastric region. As the disease progress and involve the parietal peritoneum, the somatic pain innervation gets activated and patients feels the pain in the exact location of the pathology. Further, this lower right pain worsens with pressure and thus the patient tends to keep his abdominal muscles tense to prevent movement of the abdominal wall. This is known as guarding.

Incomplete malrotation and fixation

During normal fetal development, the three divisions of the GI tract, i.e., the foregut, midgut and hindgut, herniate anteriorly out of the abdominal cavity and then undergo a 270º counterclockwise rotation. This rotation revolves around the superior mesenteric vessels. Subsequently, the three gut divisions re-enter the abdominal cavity.

Then, parts of the rotated gut become fixed to the posterior abdominal wall. Incomplete malrotation refers to any variation of the normal rotation and fixation. Such malrotation results in various anatomical anomalies such as the one described in this case. Had this patient’s appendix not become inflamed it is likely this anatomic variant would not have caused the patient any GI problems.