Clinical Exposures: Incidental finding of a peritoneopericardial hernia in a cat

A castrated male domestic longhaired cat of unknown age was presented for a preanesthetic evaluation before a dental treatment. The cat was bright, alert, and responsive. A physical examination revealed a palpable pectus excavatum and severe gingivitis with dental tartar. The cat's temperature and heart and respiratory rates were normal. No abnormalities were identified on thoracic auscultation. The owner had not reported that the cat was symptomatic.

RADIOGRAPHIC FINDINGS

A thoracic radiographic examination (Figures 1-3) done as part of the preanesthetic evaluation revealed a caudoventral deviation of the xiphoid process and productive remodeling changes at the juncture between the seventh and eighth sternebrae. A mild diffuse bronchointerstitial pattern was noted, which may have resulted from a chronic respiratory disease such as feline asthma.

Figure 1. A left lateral thoracic radiograph reveals an enlarged cardiac silhouette and a linear soft tissue band (arrow) connected to the diaphragm, caudoventral deviation of the xiphoid process, and a diffuse bronchointerstitial pattern.

The cardiac silhouette was markedly enlarged on all views, causing an elevation of the tracheal carina as seen on both lateral views (Figures 1 & 2). The right border of the cardiac silhouette was outlined by a fat opacity (Figure 2), which was thought to be the falciform fat. The size of the pulmonary vessels was normal. On the left lateral view, a dorsal peritoneopericardial mesothelial remnant connected the cardiac silhouette with the cranial diaphragmatic border (Figure 1).

Figure 2. A right lateral thoracic radiograph shows the cardiac silhouette outlined by a fat opacity.

On the ventrodorsal view (Figure 3), a pleural fissure line was visible between the right cranial and middle lung lobes. This fissure line could indicate previous pleuritis. Partial atelectasis of the caudal subsegment of the left cranial lung lobe was also seen, with an associated lobar sign. A coexisting lobar infiltrate could not be ruled out. As a result of the atelectasis, a mediastinal shift to the left was present. Radiographic attenuation of the left caudal lobar bronchus was also seen. In addition, a loss of normal diaphragmatic contour with confluence with the cardiac silhouette was noted. Also on the ventrodorsal view, a small mineralized interstitial nodule could be seen in the right fifth intercostal space. This nodule could represent a benign nodule such as pulmonary osteoma, an old inflammatory lesion such as an abscess, or an early pulmonary mass.

Figure 3. A ventrodorsal thoracic radiograph reveals partial atelectasis of the caudal subsegment of the left cranial lung lobe (arrow) and a pleural fissure line between the right cranial and middle lung lobes.

DIAGNOSIS

Because of the loss of clear diaphragmatic outline, the enlarged cardiac silhouette with normal-sized pulmonary vessels, and pectus excavatum, congenital peritoneopericardial hernia was the most likely diagnosis.

DISCUSSION

Peritoneopericardial hernia is the most common congenital diaphragmatic defect in dogs and cats.1 This condition often goes unnoticed for years, and many cases are discovered incidentally on radiographs. It is often associated with abnormalities of the sternum, such as pectus excavatum, as seen in this cat. Abdominal viscera can herniate into the pericardial sac; in most cases, the liver, bowel, or falciform fat are involved.

The radiographic features of peritoneopericardial hernia are

• A dorsal peritoneopericardial mesothelial remnant—a linear soft tissue band ventral to the caudal vena cava connecting the cardiac silhouette with the diaphragm; this remnant represents the dorsal aspect of the hernia. It is seen better on lateral views but can sometimes be seen also on a ventrodorsal or dorsoventral view.

• Global enlargement of the cardiac silhouette

• Inhomogeneous opacities within the cardiac silhouette due to abdominal viscera

• A silhouette sign between the cardiac apex and the cranioventral diaphragm

• In some cases, a small or absent liver with cranial displacement of the stomach on abdominal radiographs

Differential diagnoses should include other causes of generalized cardiomegaly, such as pericardial effusion and congenital or acquired cardiac disease. Further diagnostic tests should include echocardiography. Positive contrast peritoneography may also aid in diagnosis. If intestinal herniation is suspected, upper gastrointestinal contrast studies are recommended.

Surgical correction is recommended in patients with clinical signs. A patient with an uncorrected hernia may remain free of clinical signs, but there is always a risk of hepatic or splenic incarceration, bowel obstruction, and, in rare cases, cardiac tamponade.

In this case, the owners declined additional procedures and the cat was lost to follow-up.

This report was provided by Michal O. Hess, DVM, 620 Stephen Hands Path, East Hampton, NY 11937. Dr. Hess's current address is 17 Hedges Banks Drive, East Hampton, NY 11937.

REFERENCE

1. O'Sullivan ML. Peritoneopericardial diaphragmatic hernia. In: Coté E, ed. Clinical veterinary advisor: dogs and cats. St. Louis, Mo: Mosby Elsevier, 2007;836-837.

SUGGESTED READING

1. Biery DN, Owens JM. Radiographic interpretation for the small animal clinician. 2nd ed. Baltimore, Md: Williams & Wilkins, 1999;214-215.

2. Fossum TW. Surgery of the lower respiratory system: pleural cavity and diaphragm. In: Small animal surgery. 1st ed. St. Louis, Mo: Mosby, 1997;685-687.