Ultrasonographical examination of feline adrenal glands: intra- and inter-observer variability

Abstract

Interpretation of ultrasonographical measurements requires an understanding of the source and the magnitude of variation. A substantial part of the variation can be attributed to the observer, the equipment or the animal. The aim of this study was to evaluate which adrenal gland measurement is the least variable within and between observers. Three experienced ultrasonographers examined six cats at three different times on the same day, more than 1 h apart, according to a strict scanning protocol. Seven ultrasonographical measurements were performed on each adrenal gland (maximal length on sagittal images, maximal height at the cranial and caudal poles on sagittal and transverse images, and maximal width of the cranial and caudal poles on transverse images). Height measurements in both planes showed the lowest variability within and between observers compared with length and width measurements. Descriptive ultrasonographical features, such as echogenicity of the gland, presence of hyperechoic spots or layering assessment, demonstrated satisfactory-to-good intra- and inter-observer agreement, whereas the shape assessment showed very poor inter-observer agreement. The results of this study describe a reliable scanning protocol that can be the basis for future adrenal ultrasonographical examinations for cats suspected of adrenal disease (eg, hyperaldosteronism, hyperadrenocorticism, sex hormone-producing tumours).

Peculiarities of feline hyperadrenocorticism: Update on diagnosis and treatment

“…19 Combes et al (2014) found there was least inter- and intra-observer variability in adrenal height measurements. 62 Bilateral measurements of adrenal length and height of cranial and caudal poles should be recorded during ultrasonographic investigation of adrenal gland size (Figure 9). Most cats with PDH have bilaterally symmetrical adrenal gland enlargement; however, in some, adrenal size is within the reference interval, and rarely unilateral adrenomegaly is identified.…”

Feline abdominal ultrasonography: what’s normal? what’s abnormal? The adrenal glands

“…A d r e n a l g l a n d s i z e Several different methods have been proposed for measuring the size of the feline adrenal glands on ultrasound and, although the overall level of observer agreement is high, it is somewhat variable depending upon the method used. 12 Measuring the dorsoventral height of the adrenal gland in either the sagittal or transverse plane has been shown to be more reliable (least intra-and interobserver variability) than measuring either the length in the sagittal plane or the width in the transverse plane. 12 It was suggested that this may be explained by poor definition of the medial and lateral gland margins relative to the dorsal and ventral borders, due to the close association with the aorta (left adrenal gland) and the caudal vena cava (right adrenal gland).…”

“…12 Measuring the dorsoventral height of the adrenal gland in either the sagittal or transverse plane has been shown to be more reliable (least intra-and interobserver variability) than measuring either the length in the sagittal plane or the width in the transverse plane. 12 It was suggested that this may be explained by poor definition of the medial and lateral gland margins relative to the dorsal and ventral borders, due to the close association with the aorta (left adrenal gland) and the caudal vena cava (right adrenal gland). 12 This data is supported in part by two earlier studies.…”

“…12 It was suggested that this may be explained by poor definition of the medial and lateral gland margins relative to the dorsal and ventral borders, due to the close association with the aorta (left adrenal gland) and the caudal vena cava (right adrenal gland). 12 This data is supported in part by two earlier studies. The first reported that measurements of the thickness and length of the adrenal glands were more reliable than measurements of adrenal width, with only measurements of the width on ultrasound differing significantly from post-mortem measurements.…”

“…12 This is similar to the situation in dogs and it has been postulated that this may be due to a similarity in echogenicity and close contact between the cranial pole of the adrenal gland and the caudate liver lobe and caudal vena cava. 12,13 In the light of the above, care should be taken prior to measurement to maximise the diameter of the adrenal gland in the long-axis view and minimise the diameter in the short-axis view to avoid obliquity and, consequently, under-or overestimating its diameter. 5 Normal adrenal gland size in cats varies somewhat depending upon the reference used (Table 1).…”