Peritoneal Cavity and Gastrointestinal Tract | Ultrasound Text Manual

▶ Indications
▶ Preparation
▶ Scanning Technique
▶ Normal Gastrointestinal Tract
▶ The Stomach
▶ Small and Large Bowel
▶ Ascites
▶ Masses in the Bowel
▶ Suspected Appendicitis

Ultrasound is an accurate way of locating free fluid in the peritoneal cavity.

USG Indications for Peritoneal cavity and Gastrointestinal Tract 

Indication for Adults

• Suspected ascites and peritonitis
• Abdominal mass
• Suspected appendicitis (particularly to exclude other conditions)
• Localized abdominal pain

In Children

• Localized pain and abdominal masses
• Suspected hypertrophic pyloric stenosis
• Suspected intussusception
• Suspected but indeterminate appendicitis
• Ascites and pritonitis 

Preparation for PC and GT ultrasound scan

Preparation of the patients

The patient should take nothing by mouth for 8 hours preceding the examination. If the fluid is desirable, only water should be given, If the symptoms are acute, proceed with the examination.

Infants- a clinical condition permitting- should be given nothing by mouth for 3-4 hours preceding the examination. If the child is vomiting and suspected of having hypertrophic pyloric stenosis, a warm, sweet, non-aerated drink is necessary to fill the stomach so that it is possible to check for reflux and observe the passage of fluid through the pyloric channel.

Position of the patients 

The patient should be lying on his or her back (supine) and may be turned obliquely if necessary. It may be useful to scan the patient's erect.

Choice of Transducer

For adults, use 3.5 MHz transducers.

For children or thin adults, use 5 MHz or 7.5 MHz transducers.

Setting the correct gain

Start by placing the transducer centrally at the top of the abdomen (the xiphoid angle). Angle the beam to the right side of the patient to image the best image.

Scanning technique for Peritoneal Cavity and Gastrointestinal Tract

Start with longitudinal scans, covering the whole abdomen; then ass transverse and oblique scans, with pressure if necessary to displace the gas in the bowel.

If ascites is suspected, Correlation with X-rays may be helpful because ultrasound cannot exclude perforation of the bowel. Review anterior-posterior supine and errect (or decubitus) projections.

Normal gastrointestinal tract different anatomical parts

The different anatomical parts of the gastrointestinal tract can be recognized.

• Oesophagus
• Stomach
• Small and Large bowel

The Oesophagus

The abdominal part of the esophagus can be visualized with longitudinal scans, lying inferior to the diaphragm and anterior to the aorta. With transverse scans, the esophagus is seen behind the left lobe of the liver.

The Stomach

When empty, the fundus of the stomach will be star-shaped and easily identified. The body of the stomach will be seen on transverse scanning, just anterior to the pancreas. If there is confusion, give the patient one or two glasses of water to distend the stomach.

Small and large bowel 

The appearance of the bowel varies greatly depending upon the degree of fullness, the liquid content, and the number of feces and gas. Normal peristalsis may be seen on scanning. If the bowel is full of fluid, there will be characteristic mobile echoes. Peristalsis is usually seen in the small bowel but not always in the colon.

With ultrasound, the wall of the intestine is seen as two layers: an external hypoechogenic layer (the mucosa in contact with the gas in the bowel). The muscle wall is seldom more than 3 mm thick, depending on the part of the bowel and the degree of filling.

The gas within the bowel is hyperechogenic and may produce reverberation artefacts and an acoustic shadow posteriorly. While fluid within the bowel is echo-free or may produce some echoes due to feces.

The normal movements due to respiration should be recognized and differentiated from peristalsis.

On which position of scanning do we see Intraperitoneal fluid (ascites)?

The patient should lie on his or her back while the whole abdomen is scanned, and then obliquely on the right or left side as each flank is scanned. If there is excessive gas in the bowel, the hands/knees position can also be used. When searching for fluid, scan the most dependent part of the abdomen in all positions. Fluid will appear as an echo-free area.

Small quantities of fluid will collect in two areas of the abdomen:

1. In women, in the rectouterine cul-de-sac (the pouch of Douglas).
2. In women and men, in the hepatorenal recess (Morrison's pouch).

With greater quantities of fluid, the flank spaces (parietocolic gutters) will contain fluid. As the quantity increases, the fluid will fill the whole abdominal cavity. The bowel loops will float in the fluid, bringing the intraluminal gas close to the anterior abdominal wall, and will move as the position of the patient changes. If mesentery is thickened by malignant infiltration or by infection, the bowel will be less free to move and there will be fluid between the abdominal wall and the intestinal loops.

Ultrasound cannot distinguish between ascites, blood, bile, pus and urine. Aspiration is necessary to identify the fluid.

Adhesions in the peritoneal cavity cause septation and fluid may be obscured by intraluminal or extraluminal gas. Multiple scans in different positions will be required.

Large cysts may simulate ascites. Scan the whole abdomen for fluid. particularly the flanks and pelvis.

Ultrasound helps needle aspiration of small quantities of fluid, but training is required.

Masses in the Bowel 

When a bowel mass is identified, liver metastases must be excluded. As well as enlarged, echo-free mesenteric lymph nodes. Normal lymph nodes are seldom seen by ultrasound. 

1. Solid masses in the bowel may be neoplastic, inflammatory (e.g. amoebic), or due to Ascaris. Bowel masses are usually kidney-shaped. Ultrasound can show wall thickening and an irregular. swollen and ill-defined outline. Infection or spread of a tumor may cause fixation, and associated fluid may be due to perforation or hemorrhage. Localization may be difficult.

2. Solid masses outside the bowel. Multiple, often confluent and hypoechogenic masses suggest lymphoma or enlarged lymph nodes. In children in the tropics, consider Burkitt lymphoma and scan the kidneys and ovaries for similar tumors. However, the ultrasound differentiation of lymphoma from tuberculous adenitis can be very difficult.

Retroperitoneal sarcoma is uncommon but may present as a large. solid mass of varying echogenicity. Necrosis may occur centrally, appearing as a hypoechogenic or non-homogeneous area due to liquefaction.

3. Complex masses

Abscess: may be anywhere in the abdomen or pelvis. It is often tender, with associated fever, poorly outlined, and irregular. Apart from an appendiceal abscess, consider:

- colonic diverticulitis with perforation: the abscess is usually in the left lower abdomen;

- amoebiasis, with perforation: the abscess is usually in the right lower abdomen, less often on the left side or elsewhere:

- perforation of a neoplasm: the abscess can be anywhere;

- tuberculosis or other granulomatous infections: the abscess is commonly on the abdomen, but can be anywhere;

- regional ileitis (Crohn disease), ulcerative colitis, typhoid, and other bowel infections: the abscess can be anywhere:

- perforation by parasites, e.g. Strongyloides Ascaris or Oesophagostomum: the abscess is usually in the right lower abdomen, but can be anywhere. (Ascaris may be identified in cross-section or as long, tubular structures:

It is often easy to identify an abscess, but it is seldom possible to identify the cause.

A hematoma appears as a cystic or complex mass, similar to an abscess but often apyrexial. A clinical history of recent trauma or anticoagulant therapy is important. Haematomas may show central debris and liquefaction and may be loculated. Search also for free abdominal fluid.