Ultrasonographic assessment of normal jugular veins in standardbred horses

Ultrasonography is the most common imaging technique to evaluate jugular vein anatomy and flow and to detect thrombophlebitis. However, definitive information about the normal jugular ultrasonographic measurements in horses are not reported until now. Therefore, this study aimed: a) to establish a reference range of diameters and wall thickness of the jugular vein in Standardbred horses b) to relate diameters and wall thickness to the animal size, sex and age. Thirty-nine Standardbred horses, 4 males and 35 females, aged 12.3 ±2.8(3-22) years, that had no i.v. injections in the last 6 months, were included. Weight, neck length, height at withers were measured. Diameters and wall thickness of both jugular veins were measured at cranial (CrS), mid (MdS) and caudal (CaS) sites of the neck after 10 seconds of digital compression at its base. Mean ± SE, median, minimum and maximum values for each measurement were calculated. In order to evaluate the influence of age, sex, laterality and size, a multivariate analysis of variance (MANOVA) was applied(P<0.05). In transverse scan, the diameters were: long-axis (LA) 2.28±0.24, 2.24±0.27, 2.08±0.37cm; short axis (SA) 1.58±0.22, 1.55±0.33, 1.48±0.3cm; thickness were: superficial (SWT) 0.065±0.01, 0.065±0.02 and 0.067±0.014cm; deep (DWT) 0.071±0.011, 0.072±0.016, 0.064±0.011 cm respectively in CrS, Mds and CaS. In longitudinal scan: LA were 1.56±0.28, 1.46±0.22, 1.38±0.3cm respectively; SWT were 0,08±0.011, 0.08±0.013, 0.08±0.014cm; DWT were 0.08±0.008, 0.08±0.012, 0.08±0.011cm respectively in CrS, MdS and CaS. SWT was significantly higher in MdS in males, whereas parameters affected by age were: LA in CrS (P=0.0362), in MdS (P=0.0078) and in CaS (P=0.0006), and SA in transverse scan in CdS (P=0.0043); SWT in CrS (P=0.0047) and in CdS (P=0.0143);DWT in CdS (P=0.0002); in longitudinal scan diameters in CrS(P=0.0163), in MdS (P=0.0008) and in CdS (P=0.0128) and DWT in CdS (P=0.0262). Laterality and size were not related to the veins‘ measures. The range of jugular vein diameters and wall thickness varied considerably and were not related to the body size. Differences observed in sex may be related to the intravenous injections received by horses during their race career, that is normally longer in the males. Ageing of the vascular walls is largely studied in human medicine, but no information are available about the influence of the age on the structure of the veins in the horse. Limits of the study were the low number of male horses and the difficulty to include sound horses that did not receive any iv injection during their life. In conclusion, the determination of reliable reference values for jugular vein measurements at rest in horses might be useful both for clinical procedures and diagnosis of pathological conditions, especially in asymptomatic or paucisymptomatic thrombophlebitis. A routine ultrasound screening of the jugular vein can provide an early diagnosis of wall venous change, preventing the onset of a further occlusive thrombophlebitis.