Ectopic Hepatic Parenchyma Attached to the Diaphragm: Simulating a Pulmonary Mass in a Cat

Introduction

Ectopic livers are autonomous islands of normal hepatic parenchyma located outside the liver without any connection to it. Rarely, ectopic liver can cause clinical symptoms. Hepatic diaphragmatic herniation resembling a pulmonary mass is well documented in cats.^1–3 Ectopic hepatocellular carcinoma has been reported in a dog.⁴ The authors’ review of the literature revealed a solitary case of pericardial ectopic liver in a cat.⁵ To the authors’ knowledge, abnormally positioned normal hepatic tissue has not been reported in a cat. Primary pulmonary neoplasia is also uncommon in cats. The present report discusses a case that presented a diagnostic dilemma.

Human literature indicates that liver ectopia can occur as a result of migration of the liver during embryologic development, development of an accessory lobe of the liver with atrophy, or regression of the original connection to the main liver.^6–8 Liver ectopia is usually found during exploration for other causes. Ectopic hepatic parenchyma has been reported at various intraperitoneal or intrathoracic locations; ectopic hepatic tissue attached to the gallbladder and in the subdiaphragmatic region has been described in humans.^6–10 Review of human literature further suggests that ectopic hepatic tissue is predisposed to the development of benign and malignant lesions and is susceptible to the same risk factors as the liver.⁶ The cat presented in this report had ectopic hepatic tissue attached to the diaphragmatic wall.

Case Report

A 9-year-old, 6.5-kg, castrated male, domestic shorthair cat was presented for further evaluation of a right caudal pulmonary mass and partial anorexia. Prior to referral, the cat was presented to the referring veterinarian for difficulty in jumping up. No significant neurological deficits were noted besides some pain on lumbar palpation, and the cat was treated with injectable dexamethasone (1.5 mg intramuscularly) and prednisone (5 mg orally q 24 hours with a tapering schedule). Survey radiographs revealed a right caudal pulmonary mass. Significant past medical history included injuries from an automobile accident approximately 8 years earlier.

On presentation, the cat appeared bright and alert. The abdomen was slightly distended with no evidence of pain or discomfort on deeper palpation. The remainder of the physical examination was unremarkable, except for mild to moderate periodontal disease. A complete blood count, serum biochemical analysis, and thyroid profile revealed no significant abnormalities. Borderline hyperthyroidism was noted on the thyroid profile, with total thyroxine (T4) and tri-iodothyronine (T3) being in normal range; however, the free T4 (2.91 μg/dL; reference range 0.5 to 2.5 μg/dL) was slightly elevated. Routine urinalysis indicated concentrated urine (urine specific gravity of 1.059) with acellular sediment. The cat tested negative for retroviruses. Repeat thoracic radiographs revealed a solitary, well-defined, soft-tissue mass at the right caudoventral region of the thoracic cavity [Figures 1, 2].Abdominal sonography was also unremarkable, except for bilateral hyperechoic renal cortices.

A right sixth intercostal space thoracotomy was performed for an exploration. A mass was found at the right side of the diaphragm that communicated with the vena cava. The mass was excised. The venous bleeder to the vena cava was ligated, and the mass was submitted for histopathology. No other gross pulmonary or pleural pathology was noted. Postoperatively, a thoracostomy tube was placed. The ribs were closed with simple interrupted sutures. Closures of muscle, fascia, subcutaneous tissue, and skin were routine.

Microscopically, the examined tissue sections consisted of portions of normal hepatic parenchyma resembling a normal hepatic lobe [Figures 3, 4]. Scattered throughout the sections were areas of variable extramedullary hematopoiesis and hepatocellular vacuolar degeneration and cholestasis. No evidence of neoplasia was noted. No complications were observed in the postoperative period, and a favorable prognosis for complete recovery was discussed with the owners. Approximately 12 months after the surgical treatment, a telephone interview with the owners revealed that the cat was having no signs of respiratory distress and appeared to be doing well.

Discussion

To the best of the authors’ knowledge, a primary pulmonary or diaphragmatic ectopic liver has not been reported in a cat. In the present case with the history of serious trauma or intraabdominal injury, the authors suspect that ectopic liver at the diaphragm was a sequela to traumatic injury. Because of the comparative rarity of this anatomic anomaly, the authors are presenting this as a new case and providing a brief review of the literature. Cases such as this have already been reported in humans and a dog.

A favorable perioperative survival can generally be anticipated in dogs and cats with diaphragmatic hernia.^11–13 However, one report suggested that older cats or cats that have low to mildly increased respiratory rates and concurrent injuries are more likely to die after surgical repair of traumatic diaphragmatic hernia.¹⁴ Herniation of abdominal viscera into the thoracic cavity is known to develop after blunt or penetrating trauma to the lower thorax, or it may be caused by a congenital defect in the diaphragm.¹⁰ The diaphragmatic hernia may or may not show any signs. Although lung herniation is considered to be a concomitant injury that is not life-threatening in most cases, its combination with severe lung contusion, multiple injuries, and associated hemothorax can be life-threatening in some cases.¹⁰ An acquired diaphragmatic hernia, as noted in the current case, is a rupture of the diaphragmatic muscle. As the abdominal contents such as the stomach and liver are forced against the diaphragm, a tear or rupture of the muscle occurs. Once an opening in the muscle occurs, abdominal contents (such as the liver, stomach, or intestines) may herniate through the rupture, enter the pleural space, and compress the lungs.^10–14

The cat was initially presented for some rear-limb weakness with no apparent respiratory signs. The initial survey radiographs revealed an incidental finding of a suspected pulmonary mass. Diaphragmatic hernia resembling a pulmonary mass has been described in a cat.³ However, in the case of this report, the thoracic radiographic findings were not completely consistent with a diaphragmatic hernia; therefore, an initial tentative diagnosis of primary pulmonary mass was made.

In the current case, the cat was asymptomatic for the signs of diaphragmatic hernia or primary pulmonary neoplasia. No respiratory signs were noted on the examination or reported by the owners. The radiographic findings of diaphragmatic hernias are well known,¹⁵ but when incidentally found in an asymptomatic patient on routine survey radiographs, the appearance of diaphragmatic hernia may mimic many other conditions. Liver, stomach, and small intestine are more commonly herniated. Diaphragmatic hernias commonly occur in cats after an automobile accident.¹⁵ The present case did have a history of prior automobile accident.

Radiography is the most important diagnostic method; however, in some cases (especially with pleural effusion), radiographic findings might not be diagnostic. In such cases, contrast studies such as esophagram, sonography, or computed tomography (CT) might aid in establishing a diagnosis. The authors did not perform a CT scan in this case, because the owner decided for surgical removal of the solitary mass. With advances in CT technology, the new-generation scanners have a faster gantry rotation that allows imaging of the thoracic parenchyma with excellent resolution. Although a CT scan was not performed in the current case, the authors suggest, based on other pulmonary CT studies,^16,17 that CT evaluation should be considered in asymptomatic cases such as the one discussed here.

Conclusion

This solitary case report demonstrates that ectopic liver should be considered as a possible differential diagnosis for primary caudal pulmonary mass. To the authors’ knowledge, this is the first reported case of an ectopic hepatic tissue attached to the thoracic side of the diaphragm in a cat.