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What’s Your Diagnosis? Identifying Peritoneal Air

Visualization of structures in the abdominal cavity is due to the differential radiopacity of the soft tissue structures, which are primarily surrounded by fat.

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Signalment: 15–year-old female, spayed domestic shorthair with history of gastrointestinal lymphoma.

History: Patient presented for labored breathing and lethargy. Thoracic radiographs were obtained.

Questions

  1. What are the primary findings?
  2. What do you think is the primary reason for the clinical signs?

Radiographic Findings: The heart is mildly enlarged and the atria are prominent, suggestive of cardiomyopathy. The pulmonary parenchyma and pulmonary vessels are normal. In the viewable cranial abdomen, there are multiple, free, round gas bubbles noted. Of particular note is the bubble of air noted in the vicinity of the liver on the left lateral view adjacent to the diaphragm.

There are other accumulations of air noted as small gas bubbles that are not conforming to the GI tract in the cranial ventral abdomen. The right side of the abdominal side of the diaphragm is visible on the VD view. There is also loss of surface detail noted in the midventral abdomen around the small bowel.

Radiographic Interpretation: Free peritoneal air. Possible effusion in the mid-abdomen. Possible mild cardiomyopathy without evidence of heart failure.

Visceral Surface Detail: Visualization of structures in the abdominal cavity is due to the differential radiopacity of the soft tissue structures, which are primarily surrounded by fat. This is the key factor, as there is very little free peritoneal fluid present in the normal dog or cat.

Enhanced visualization of visceral surfaces in the abdomen can be due to pneumoperitoneum. Free air in the peritoneal space allows visualization of structures that are not normally seen; examples include the cranial pole of the right kidney and the visceral surface of the stomach and the diaphragm. Possible causes for pneumoperitoneum include iatrogenic causes (surgery, peritoneocentesis), penetrating wounds, ruptured gastrointestinal tract or gas-forming bacteria.

Diagnosis of pneumoperitoneum is dependent upon the amount of free air present. Sometimes routine radiography may be sufficient. However, the use of positional radiographs may be necessary to detect smaller amounts of air. This utilizes a horizontally directed X-ray beam. Often, left lateral recumbency will allow air to accumulate in the right cranial quadrant, away from the fundus of the stomach.

Loss of visceral detail can be due to a number of causes such as lack of abdominal fat in young or emaciated animals. This is usually not clinically significant. Other causes include accumulation of soft tissue opacity, which silhouettes with abdominal structures such as fluid or cellular infiltrates. Fluid such as transudates, modified transudates or exudates can cause loss of detail. Cellular infiltrates such as carcinomatosis can also cause loss of detail.

Compression of abdominal contents can also cause a loss of visceral detail. This often is seen with large mass effects in the abdomen such as occurs with neoplasia or a large and distended urinary bladder. Often, ultrasound can be used to help determine the loss of visceral detail—to differentiate fluid accumulation versus a mass effect. It can also be used to obtain a sample of fluid, particularly if there is a small amount present.

In this particular patient in this case, there was no history of recent surgery or a penetrating wound. Therefore, ruptured viscus, especially given the history of gastrointestinal lymphoma, would be most likely. The loss of detail in the mid-abdomen may be due to a small volume of free fluid (commonly seen in rupture of the GI tract as peritonitis sets in) or from small mass effects (enlarged lymph nodes from the lymphoma).

The cause of the labored breathing is not related to a primary respiratory problem but likely is a response to either pain or possibly changes related to peritonitis and sepsis.

Identification of free air is critical, as immediate attention will maximize the prognosis in many patients.

Summary: Changes in visceral detail are often subtle but of paramount importance in identifying problems, especially when the clinical signs are vague. Careful evaluation of all portions of the images is also important as important information can be obtained, as has been shown in this particular case. <HOME>

Anne Bahr, DVM, MS, Dipl. ACVR, is a consulting radiologist with PetRays Veterinary Radiology Consultants in Spring, Texas.

This program was reviewed and approved by the AAVSB RACE program for continuing education.  Please contact the AAVSB RACE program at race@aavsb.org should you have any comments/concerns regarding this program’s validity to the veterinary profession.

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