Ultrasound and the Nonacute Abdomen: The Abdominal Organs

The ability of ultrasound to detect abnormalities of the kidneys, liver, and spleen has made tremendous strides over the past 10 years due to technological advancements in ultrasound equipment and increased availability of skilled equine ultrasonologists. As our knowledge base continues to grow, increased awareness is important for owners and veterinarians to understand the diagnostic potential of abdominal ultrasound. Evaluation of abdominal organs is best performed as part of a complete abdominal ultrasound exam. Ultrasound-guided procedures are often required to differentiate between various infectious, inflammatory, and neoplastic disorders.

1. Introduction

Evaluation of the abdominal organs, including the kidneys, liver, and spleen, is generally performed as part of a complete ultrasound examination in nonacute patients.¹  Many horses with hepatic, renal, or splenic abnormalities present with nonspecific clinical signs^{3– 6}  similar to those in horses with gastrointestinal tract disorders. Complete blood count (CBC) and serum chemistry analysis may be unremarkable or show only evidence of inflammation such as hyperfibrinogenemia and hyperglobulinemia. Subsequently, a full exam is required to maximize diagnostic yield in many cases. In other horses, clinical exam findings and serum biochemistry analysis may indicate primary renal or hepatic disease, in which case the examiner may choose to focus on the urinary tract or liver, respectively. Although horses with abdominal organ disorders infrequently present as acute colic patients, cursory examination of abdominal organs can yield important information during routine colic ultrasound exams.

Admittedly, mastery of abdominal ultrasound requires experience and patience, much more so than basic ultrasound of the acute abdomen. Similar to any anatomic region, however, cursory examination is possible by a motivated practitioner equipped with appropriate ultrasound equipment. It is equally important for field practitioners to understand our increased ability to diagnose and treat disorders of abdominal organs in the referral setting. Ultrasound findings often help guide treatment planning, including the need for medical therapy or surgical intervention. Not only do we gain valuable information about the appearance of abdominal organs, ultrasound-guided biopsy and/or aspirate can be used to determine the underlying etiology, to establish an appropriate treatment plan, and for prognostication.^1–2

Ultrasonographic Technique

A low-frequency (2–5 MHz) curvilinear transducer is necessary to evaluate abdominal organs in the adult horse due to their deep location (15 to 30 cm) relative to the skin surface. This transducer is available for most of today’s ultrasound machines, the majority of which are able to obtain exceptionally high-quality abdominal images. In contrast, a rectal transducer can only penetrate to 5 to 10 cm, which is insufficient to image the left kidney and the majority of the spleen, liver, and right kidney from the transcutaneous window. A rectal transducer can be used to image the caudal portion of the left kidney and spleen during transrectal examination.

For the highest quality images, the entire abdomen should be clipped with #40 blades, especially in older, obese, or thick-coated horses that tend to image poorly (Fig. 1). Alcohol saturation can produce diagnostic quality images, but the subtle nature of many ultrasonographic findings in the nonacute abdomen may not be detectable without clipping. After clipping, the skin should be cleaned with a wet sponge to remove dirt and debris, and ultrasound gel is then applied.
 

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