Ultrasound of the Thorax and Abdomen in the Foal

Ultrasonography in the neonate may be used in the initial evaluation to determine an anatomic location of sepsis or to evaluate for traumatic injury secondary to dystocia. It is often the first diagnostic tool applied after the physical evaluation of the foal.

1. Introduction

Ultrasonography has become a routine part of medical examination of the foal and is a valuable tool for acquiring information on structural pathology of organs within the thorax and abdomen. In the neonate, it may be used in the initial evaluation to determine an anatomic location of sepsis or to evaluate for traumatic injury secondary to dystocia. Although we often separate disorders of the thorax and abdomen into distinct categories, both body cavities are usually evaluated during the same ultrasound examination. The ultrasound examination is performed in a cranial-to-caudal manner—passing the ultrasound probe along each intercostal space, scanning from dorsal to ventral, and then sweeping the caudal and ventral abdomen behind and beneath the ribs.

2. Thoracic Ultrasound in the Foal

Disorders of the thorax in the neonatal foal include rib fractures, pneumonia, and effusions (septic, hemorrhagic, or other). Rib fractures are common in hospitalized neonatal foals, and ultrasound is considered a more accurate method of detection compared with radiography and physical examination.^1,2  Fractures are most often located within 3 cm of the costochondral junction and more commonly involve the first few ribs behind the elbow. Early on, a rib fracture may appear as a “greenstick” fracture (Fig. 1), detected on ultrasound as a slight discontinuity of the external cortical surface. Later, increasing displacement of the fracture site is detected sonographically as more separation of the fracture fragments with the distal segment usually moving medially (Fig. 2). There may be fluid or hemorrhage in the soft tissues surrounding the fracture ends with multifocal echolucent areas (Fig. 3). Some indentation (or step deformation) of the parietal and visceral pleural surfaces may also be detected. Injury to the underlying pulmonary parenchyma can vary from mild bruising with a few echogenic “comet tails” to progressively more involvement with parenchymal consolidation and occasional hemothorax or pneumothorax. Serial evaluation of the degree of displacement is recommended to determine if there is risk of cardiac injury or progressive change in the lung— either might be an indication to consider surgical stabilization versus conservative management of restricted mobility in the stall. Ultrasound can also be useful in monitoring the fracture healing process— determining when there is sufficient callus formation and fracture stability to allow more exercise. With fracture of more caudal ribs, there may be injury to the diaphragm and possible diaphragmatic hernia with intestinal structures within the pleural space (Fig. 4).
 

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