Evaluation of percutaneously obtained liver biopsy specimens is widely regarded as the most sensitive and specific antemortem diagnostic test for suspected hepatopathy in horses.1,2 Evaluation of liver biopsy specimens may establish the presence or absence of liver disease, provide a specific diagnosis, guide treatment, and help determine prognosis in cases of suspected liver disease.3 Multiple techniques for obtaining a biopsy specimen of the liver have been described, including standing laparoscopic surgery,4 blind percutaneous biopsy, and direct and indirect ultrasound-guided biopsy. Ultrasonography is also useful to visualize the echogenicity, size, and location of the liver. The abdomen is scanned for the presence of adequate liver tissue, the biopsy region is marked on the horse, and the area of interest is prepared for sterile biopsy. This technique also allows for a brief abdominal ultrasonographic examination following biopsy to ensure that hemorrhage has not occurred as a result of the procedure.
On ultrasonographic examination, the equine liver appears as a wedge of weak, homogenously distributed echoes medial to the diaphragm and ventral to the lung margin from the 9th to the 16th ICS.5–7 The liver is most commonly viewed from the right side of the abdomen in a healthy horse, but because of the possibility of atrophy of the right liver lobe in older horses, likely resulting from pressure of the right dorsal colon and cecal base, examination of the liver from the left side may be necessary.7 The left liver lobe can occasionally be imaged from the left 9th to 11th ICS and ventral to the lung margin.1,8
The greatest limitation of ultrasonographic organ localization and biopsy guidance is the inability of ultrasound to transmit through gas-filled structures and bone. These structures act as barriers to sound beam penetration and prevent observation of soft tissue structures deep to them.1 Even with the liver located in a normal anatomic position in a healthy horse, it may be deep to structures that are not able to be penetrated by ultrasound beams. Therefore, gas-filled structures such as lung and intestines positioned between the liver and body wall could inadvertently be penetrated during an attempted liver biopsy. Pneumothorax, excessive blood loss into the abdominal or thoracic cavities, or enterocentesis can occur and require medical intervention.1
Anatomic locations to perform a blind percutaneous liver biopsy are published1,9 and referenced to by many equine veterinarians. The most frequently recommended location for performing a blind percutaneous liver biopsy has been described as the right 12th to 14th ICS at approximately the level of a line drawn between the tuber coxae and the point of the olecranon, directing the needle toward the contralateral elbow joint.9 Another similar location described is the right side of the abdomen between the 10th and 11th or the 11th and 12th ribs just below a line drawn from the point of the tuber coxae to the point of the shoulder, passing the biopsy instrument caudad and ventrad through the intercostal muscles corresponding with expiration to decrease the likelihood of penetrating the lung.1
In 1 study,9 liver biopsy could not be performed in 17% (4/24) of study mares because the liver was not visualized ultrasonographically at the target zone, which is similar to but encompasses a larger area than the recommended locations for blind percutaneous liver biopsy. To the authors' knowledge, the actual frequency of ultrasonographic identification of the liver in the suggested locations for blind percutaneous liver biopsy in horses has not been reported. Furthermore, we are not aware of any study that has specifically determined the suitability of liver for biopsy at the recommended blind percutaneous liver biopsy sites in a specific population of horses. Therefore, the objectives of the study reported here were to ascertain the frequency of ultrasonographic identification of liver in the recommended location for blind percutaneous liver biopsy in middle-aged horses and to determine on ultrasonographic examination whether the liver is obscured by other organs or too thin for safe sample collection at those locations. We hypothesized that the frequency of identification of liver adequate for biopsy in the recommended locations for blind percutaneous liver biopsy is small and that the lack of sufficient liver tissue in the proposed locations could lead to serious complications resulting from biopsy including hemorrhage, peritonitis, or pneumothorax.
BD Vacutainer Serum, 10-mL plain tube, BD, Franklin Lakes, NJ.
Technos ultrasound unit, Esaote, Genoa, Italy.
1. Modransky PD. Ultrasound-guided renal and hepatic biopsy techniques. Vet Clin North Am Equine Pract 1986; 2: 115–126.
2. Durham AE, Newton JR & Smith KC, et al. Retrospective analysis of historical, clinical, ultrasonographic, serum biochemical and haematological data in prognostic evaluation of equine liver disease. Equine Vet J 2003; 35: 542–547.
3. Divers TJ, Bernard WB, Reef VB. Equine liver disease and liver failure—causes, diagnosis, and treatment, in Proceedings. 10th Bain-Fallon Memorial Lecture 1988;35–46.
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12. Nobili V, Comparcola D & Sartorelli MR, et al. Blind and ultrasound-guided percutaneous liver biopsy in children. Pediatr Radiol 2003; 33: 772–775.