By: Dr. Dorrestein Gerry M. DVM, Dr Dr hc, Dip ECVP – AVD – Veterinary Pathologist for Exotic Animals and Maguire Rina, BVSc hons 1 ABVP Dip ECM, DACEPM – Beecroft Animal Specialist & Emergency Hospital- Exotic Companion Mammal Specialist.
Introduction
Liver lobe torsion is considered an uncommon disease in domestic animal species; however in pet rabbits its prevalence and clinical significance has been reported in several recent publications. (Ozawa et al, 2022, Sheen et al, 2022, Summa and Brandão, 2017). In a retrospective study of records from four institutions between 2010 and 2020; a prevalence of liver lobe torsion of 0.7% was reported (82/11,402)(Ozawa et al, 2022). The diagnosis of a liver lobe torsion was made via abdominal ultrasonography in all 82 rabbits. In another published study, 40 cases were diagnosed over five years (Sheen et al, 2022). A referral specialist hospital also reported a case series of 16 liver lobe torsions in rabbits over a five-year period (Summa and Brandão, 2017).
The objective of this short review is to raise awareness of this potentially under reported disease in pet rabbits. The diagnosis, pathology and treatment of liver lobe torsions will be discussed to aid clinicians to reach a diagnosis. A definitive diagnosis can only be made through histopathology. In 2023 to date, 11 histopathology liver specimens have been submitted to AVD and were confirmed to be liver lobe torsions. This indicates a high prevalence of this disease in this region. Of these cases, nine originated from Singapore and two cases from Hong Kong.
Pathology
Several lobes can be affected but the caudate lobe on the right-hand side appears to be the most common lobe undergoing torsion. The caudate lobe, which sits over the right kidney, could be predisposed due to its narrow attachment at the hilus that acts as a stalk about which it can rotate (Vetlexicon 2023). In some cases, a different lobe can be involved. Although the cause of liver lobe torsion is unknown, predisposing factors are thought to include surgical or external trauma, congenital absence of hepatic ligaments, or dilation of abdominal organs (Graham and Basseches, 2014). Lop breeds seem to be overrepresented, but other breeds can be affected as well (Ozawa et al, 2022).
Liver lobe torsion leads to occlusion of the venous return which causes acute congestion within the affected lobe. Vascular and cellular compromise causes necrosis, increases in circulating liver enzymes which can then lead to effusion, hemoabdomen, shock and even death (Graham and Basseches, 2014). In severely affected animals, disseminated intravascular coagulation (DIC) secondary to ischemic by-product release into the circulation is usually the cause of death. Occasionally the affected and enlarged lobe will rupture causing fatal haemorrhage (Harcourt-Brown, 2023).
History and Physical Exam
The most common clinical signs of rabbits presenting with liver lobe torsion included hyporexia or anorexia, lethargy, abdominal pain and tachypnoea, dehydration, increased intestinal gas, firm stomach, decreased borborygmi, dull mentation, hypothermia and decreased faecal production of at least 24 hours. A mass or palpable liver edge in the cranial abdomen can be noted. (Graham et al, 2014; Ozawa et al, 2022). Other clinical signs included urinating outside the litter box, diarrhoea, not drinking, and behaviour changes. Due to the non-specific findings on the physical exam, many cases can be easily misdiagnosed as primary gastrointestinal stasis. (Graham et al, 2014; Ozawa et al, 2022). In one study, a finding that was statistically associated with a poor prognosis was tachycardia (Ozawa et al, 2022). Tachycardia can occur secondary to pain, hypovolemia, sepsis, cardiac failure, stress, or various types of shock.
Diagnosis
A complete blood count and chemistry panel should be performed for all rabbits presented for abdominal pain and gastrointestinal stasis. The most common hematologic abnormality encountered with rabbits afflicted with liver lobe torsion is anaemia which is caused by haemolysis, haemorrhage or sequestration of erythrocytes in the affected liver lobe and/or erythrocyte fragmentation. Serum biochemical abnormalities frequently seen included elevated levels of alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, blood urea nitrogen, and creatinine (Graham et al, 2014; Ozawa et al, 2022).
Abdominal ultrasonography with doppler assessment aided in the diagnosis of liver lobe torsion in all cases (Graham et al, 2014). Common ultrasonographic findings included parenchymal hyper echogenicity of the torsed lobe which is different to the other liver lobes and/or an abnormally larger liver lobe with rounded margins(Graham and Basseches, 2014, Noonan, 2022). Free peritoneal fluid is not always present. Colour flow doppler shows absence of blood flow in the affected liver lobe(s) (Figure 1-4).
Treatment
Early identification and monitoring are crucial in providing the best management route and positive treatment outcomes (Noonan, 2022). Once diagnosis is confirmed via ultrasound, clients should be advised that surgical management is the gold standard option. A liver lobectomy of the affected lobe is the treatment of choice (Graham et al, 2014; Ozawa et al, 2022; Sheen et al, 2022)(Figure 5-6). Most rabbits with caudate lobe torsions recover without complications aside from post-operative gastrointestinal stasis, which resolves with supportive care.
Figure 1 and 2
Figure 3 and 4
Sagittal ultrasonography with Doppler assessment of a caudate lobe torsion in rabbit. Figure 1 and Figure 2 Hyperechoic liver with rounded edges Figure 2 and 3 The colour doppler study over a portion of the affected lobe demonstrates lack of blood flow in the liver. Figure 4 Free fluid around the liver lobe margin. (Images courtesy of Beecroft Animal Specialist & Emergency Hospital, Singapore.
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