Anatomical distribution of meconium detected by focused abdominal ultrasound in hospitalized healthy and sick neonatal foals

Background: Meconium impaction is a common cause of neonatal colic in foals, yet its ultrasonographic appearance and distribution remain poorly characterized. Aims/objectives: This study aimed to describe the frequency, distribution, and ultrasonographic appearance of meconium in hospitalized neonatal foals using a standardized focused ultrasound (FUS) abdominal protocol. Methods: The FUS protocol included 9 acoustic windows (3 left-sided, 3 ventral, 3 right-sided) and was performed once during hospitalization by a single operator using a curvilinear transducer. Results: Thirty-six foals (16 healthy and 20 sick), aged ≤7 d, were enrolled. Meconium was identified in 19 foals: 9/16 healthy (seven ≤36 h, two >36 h), none of which were treated for impaction, and 10/20 sick foals (four ≤36 h, six >36 h), three of which received treatment. Meconium was visualized in 6/9 FUS windows, most commonly in the retrosternal window, followed by the ventrolateral windows. The sternal flexure was the most frequently involved segment of the intestinal tract (12/19 foals), followed by the right ventral colon/cecum and left ventral colon (9/19). Multiple acoustic windows were more commonly involved in sick foals. All treated foals had small colon meconium impaction, visualized through the hypo-gastric window. Meconium appeared as a ball-shaped intraluminal mass, with hypoechoic or mixed echogenicity in the large colon and hyperechoic or mixed echogenicity in the small colon. Limitations include the single-operator design, small convenience sample, and use of FUS rather than a comprehensive ultrasonographic examination. Conclusion: In conclusion, meconium detection in foals older than 36 h may represent an incidental finding. The hypogastric window should be carefully evaluated when impaction is suspected. The FUS protocol represents a promising tool for monitoring meconium distribution over time and treatment.