Ultrasonography of the umbilical remnant in foals

SONOGRAPHIC examination of the umbilical remnant is a practical procedure that is easily accomplished in the field and is generally well-tolerated by foals. The examination can be performed with the foal standing or in lateral recumbency, and sedation is not normally necessary.

No special preparation of the patient is required and the use of a generous quantity of ethyl alcohol to wet the foal’s coat is enough to obtain a good contact between the probe and the abdominal wall. Some clinicians prefer to use baby oil rather than alcohol. They report that it also provides good contact but avoids drying the skin, something that is especially important if foals are to be scanned repeatedly. If a foal has a very long or dirty coat, the abdomen should be clipped (using a number 40 clipper blade) before examination.

All umbilical remnant structures are small and located very close to the skin surface. A high-frequency linear transducer (operating at 10 to 12 MHz) gives the best results, but good images can also be obtained with a linear transrectal probe (operating at 5 to 7.5 MHz), such as those used in equine reproductive ultrasonography.

It is possible to examine four different structures (Fig 1):

• Umbilical stump

• Umbilical vein

• Umbilical arteries

• Urachus.

Imaging of the umbilical stump

The external umbilical remnant contains the umbilical vein, the two umbilical arteries and the urachus (Fig 2). These structures atrophy within a few days of birth. Abnormalities associated with the external umbilical remnant include infection, hernias, patent urachus and periumbilical disorders.

Infection

Infection is the primary disorder of the external umbilical remnant. This is characterised clinically by local swelling and/or a draining tract (Fig 3a). Ultrasound examination shows enlargement of one or more structures, with variable sonographic appearances (Fig 3b).

All the ultrasound images in this article were obtained using a wide bandwidth linear transducer operating at 12 MHz. The depth of penetration for each image is given in the individual captions.