Because of its many physiological roles, and the variety of its biological components, the liver is subject to a large variety of disease conditions, many of which manifest as a space occupying lesion or mass. Larger masses are often diagnosed first by abdominal palpation, although smaller masses are more frequently being found during sonographic examinations for other conditions.

Table. Diseases producing space-occupying hepatic lesions in dogs and cats.

 Hepatoma

 Regenerative nodule

 Hepatic adenocarcinoma

 Hepatic lobe torsion

 Choledochal cyst

 Hepatic cystadenoma or cystadenocarcinoma (cats)

 Polycystic liver disease (often associated with polycystic kidney disease)

 Biloma

 Hepatic abscess

Surgeons may be required to address these hepatic lesions with curative intent, or simply to collect diagnostic samples.

Preoperative Investigation of Hepatic Masses

A full physical examination should be undertaken, including rectal examination, to identify any other conditions that might be related to the mass. Serum chemistry and full blood count are helpful, especially where there is a suspicion that the masses might be regenerative nodules. The patient's coagulation profile should be established if surgery is being considered. Abdominal radiography may confirm presence of a soft tissue mass in the cranial abdomen, but does not usually differentiate between the different disease processes and details may be obscured by peritoneal fluid. The mainstay of initial diagnosis is abdominal sonography, which should be able to clarify whether the mass is solid or cavitary. Sonography may or may not be able to identify the origin of the mass, and with careful positioning, the sonographer should be able to determine the relationship of the mass to the large vessels, bile duct and gall bladder. Advanced imaging such as contrast-enhanced CT may be of further assistance in determining the vascularity of the mass and its proximity to the caudal vena cava and portal vein. However, with large masses that compress the adjacent viscera, it can be very difficult for any imaging modality to confidently assess degree of invasion or attachment and the potential for resection. It may not be until the abdomen is explored and the mass visualized that its resectability can be determined. Sonography is used to evaluate the non-affected liver lobes for additional masses or other abnormalities, although there is a reasonable incidence of false positive and negative results.

Fine needle aspiration biopsy is variably useful for pre-operative diagnosis. It commonly yields blood, epithelial cells and haematopoietic cells, and their significance can be hard to determine. Degenerative neutrophils and bacteria will be seen in hepatic abscesses, but may simply indicate necrosis and infection of an underlying hepatic neoplasm. In either case, presence of a septic abscess within the liver is an indication for surgical exploration. The main risks associated with fine needle aspiration are hemorrhage and release of pus or bile into the peritoneal cavity. Tru-cut biopsy may be more likely to yield a diagnosis, but for surgeons who are comfortable performing liver lobectomy and hepatectomy, surgical exploration and resection or drainage of the lesion is often performed as the next step.

Cysts

Cystic changes encountered in small animals include benign choledochal cysts, cystadenoma and cystadenocarcinoma and biloma. Biloma is most often reported following trauma or surgery. The cysts may contain bile, or may not communicate with the biliary tree at all and just contain serosanguineous fluid. In the case of bile-containing cyst, the communication with the biliary tree must be identified and closed, and patency of the bile duct confirmed, before the cyst can be treated surgically. Cysts that do not communicate with the biliary tract can be either excised, drained percutaneously using a closed-suction drain, or marsupialized. Samples should be taken for histopathology, as neoplastic cysts will obviously recur.

Abscesses

Hepatic abscesses occur quite commonly and are often a per-acute emergency. While pre-operative stabilization and support is critical, it is imperative that the abscess be drained or excised as soon as possible to reverse the septic changes occurring in the patient. Undue delays for diagnosis, imaging and even stabilization can actually be detrimental. Unfortunately, hepatic abscesses often occur in the setting of undiagnosed hepatic neoplasia, in which case the underlying diagnosis may not be made until the results of histopathology are obtained some time after the surgery. Owners of patients being explored for hepatic abscess should be warned that their pet's acute condition may resolve with surgery, but the long term prognosis cannot be determined until the histopathology is available.

Masses

Liver diseases may be infiltrative, multiple small nodules (as with metastatic neoplasia) or take the form of single masses (so-called "massive" liver tumors). They may be benign or malignant and it can be difficult to differentiate these without biopsying them. In general, benign processes tend to result in larger, slow-growing lesions that are palpated during routine physical examination, whereas malignant processes are more likely to be diagnosed as a result of hemorrhage or ascites before they become large enough to be palpated. Malignant tumors may also outstrip their blood supply, become necrotic and secondarily infected and present acutely as a hepatic abscess.

Massive liver tumors are often resectable, unless they grow into the hilus of the liver or encircle the large blood vessels. A retrospective study of 48 dogs showed the mortality rate to be low following surgery, and the long-term prognosis to be excellent with a low metastatic rate.¹ The surgical margin will be dictated by the proximity of the mass to the hilus. These masses are usually treated by complete liver lobectomy. The liver may be removed by the finger-fracture technique and ligation of blood vessels, however, use of a TA surgical stapler is quicker and usually effective. Vessel sealing devices such as the harmonic scalpel and LigaSure have also been used successfully.² The LigaSure is not recommended for sealing the bile duct as late breakdown has been documented. Anatomical techniques for isolating the liver lobes, whereby the vasculature is dissected as close to the hilus as possible, may enable removal with a greater margin than when the lobe is amputated using a stapler.³

Biliary Diversion

Biliary diversion may be achieved percutaneously, using a cholecystostomy tube, or by means of a stent placed using interventional radiology. These techniques have been reported, but are not used commonly in small animals. They do offer an attractive option for stabilization of the patient with acute, reversible bile duct obstruction such as pancreatitis. However, most biliary diversion is performed in patients with more chronic bile duct obstruction and is achieved surgically by means of cholecystoduodenostomy or bile duct reimplantation.

Requirements for Successful Surgical Management

1.  Anesthetic support

2.  Blood products

3.  Hemostasis (vessel sealing devices, surgical staplers, Gelfoam, Surgicel gauze)

4.  Long-handled surgical instruments for dissection and gentle tissue handling (Debakkey forceps, right-angled dissecting forceps, Satinsky or Cooley vascular forceps)

5.  Good knowledge of liver anatomy

6.  Understanding disease processes and underlying diagnosis

7.  Postoperative intensive care and 24 hour monitoring

References

1.  Liptak JM, Dernell WS, Monnet E, et al. Massive hepatocellular carcinoma in dogs: 48 cases (1992–2002). J Am Vet Medical Assoc 2004;225:1225–1230.

2.  Risselada M, Ellison GW, Bacon NJ, et al. Comparison of 5 surgical techniques for partial liver lobectomy in the dog for intraoperative blood loss and surgical time. Vet Surg 2010;39:856–862.

3.  Covey JL, Degner DA, Jackson AH, Hofeling AD, Walshaw R. Hilar liver resection in dogs. Vet Surg 2009;38:104–111.