CT imaging features of the normal parathyroid gland in the dog

Zusammenfassung

Gegenstand und Ziel Ziel dieser prospektiven Pilotstudie war zu beurteilen, ob die physiologische Glandula parathyroidea beim Hund computertomografisch dargestellt werden kann, und eine Beschreibung ihres CT-Erscheinungsbildes zu geben.

Material und Methoden In die Studie wurden 25 Hunde aufgenommen, bei denen aufgrund von Erkrankungen im Halsbereich ohne Bezug zu Schild- oder Nebenschilddrüse ein CT-Scan erfolgte. Einschlusskriterium waren unauffällige Befunde bei der allgemeinen klinischen Untersuchung und der Blutuntersuchung (Blutbild und blutchemische Analyse). CT-Bilder vor und nach Kontrastmittelapplikation (30–45 Sekunden nach der Kontrastmittelinjektion, frühe venöse Phase) wurden mit einem 16-Schichten-Spiral-CT unter Verwendung eines Field of View von 18 cm, einer Schichtdicke von 1 mm und einer Matrix von 512 × 512 angefertigt. Zwei Radiologen begutachteten die CT-Aufnahmen unabhängig voneinander. Die Sichtbarkeit der Parathyreoidea wurde erfasst und die Interobserver-Reliabilität ermittelt. Bei den darstellbaren Nebenschilddrüsen wurden folgende Parameter bestimmt: Größe, Dichte (in Hounsfield Units [HU], vor und nach Kontrastmittelgabe), Dichte der Schilddrüse, Abgrenzung (exzellent, mäßig, schlecht).

Ergebnisse Nur 20 bzw. 25 Nebenschilddrüsen waren durch die beiden Untersucher erkennbar. Die Anzahl differierte zwischen Nativaufnahmen und Bildern nach Kontrastmittelgabe nicht. Die Interobserver-Reliabilität hinsichtlich der Erkennbarkeit war moderat (κ = 0,40). Für Länge, Breite und Höhe der Nebenschilddrüsen (Mittelwert ± Standardabweichung) ergaben sich 4,2 × 2,5 × 2,9 mm ± 1,3 × 0,8 × 1,0 mm. Die Dichte betrug 39,7 ± 20,6 HU vor und 103,1 ± 47,1 HU nach Kontrastmittelgabe. Damit stellten sich die Nebenschilddrüsen im Vergleich zur Schilddrüse (vor und nach Kontrastmittelgabe 166,7 ± 34,3 HU bzw. 234,0 ± 60,1 HU) hypoattenuierend dar.

Schlussfolgerung Diese Studie liefert die erste Beschreibung des CT-Erscheinungsbilds der angenommen physiologischen Nebenschilddrüse beim Hund. Die Sichtbarkeit des Organs war jedoch schlecht.

Klinische Relevanz Trotz der schlechten Visualisierung der Nebenschilddrüse im CT ist sie gelegentlich wahrnehmbar. Die ermittelten Dimensionen waren teilweise größer als bisher für sonografische Darstellung beschrieben, ohne dass die untersuchten Hunde erkennbare Symptome eines Hyperparathyreodismus aufwiesen. Eine computertomografisch sichtbare Nebenschilddrüse impliziert daher möglicherweise nicht unbedingt eine Erkrankung. Weitere Studien dazu sind notwendig.

Abstract

Objective Aim of our prospective pilot study was to assess the feasibility of computed tomography (CT) to visualize the normal parathyroid gland in dogs and provide a description of its CT appearance.

Material and methods A total of 25 dogs, which received CT imaging including the neck region for diseases unrelated to the thyroid or parathyroid glands, were enrolled. Inclusion criteria were a normal physical examination, an unremarkable complete blood count and serum chemistry profile. Pre and post contrast CT images were acquired using a 16-slice helical scanner with an 18 cm field of view, 1 mm slice thickness and a 512 × 512 matrix. Post contrast images were obtained 30–45 seconds following contrast medium injection (early venous phase). CT-images were independently reviewed by 2 radiologists. Visibility of the parathyroid gland was recorded and inter-observer agreement was calculated. For all visualized parathyroid glands the following parameters were assessed: size, density in Hounsfield units (HU) on pre and post contrast images, density of the thyroid gland and border definition (excellent, moderate, poor).

Results Only 20 respectively 25 parathyroid glands could be visualized by the 2 observers. The number did not vary between pre and post contrast images. The inter-observer agreement for the identification was fair (κ = 0.40). Length, width and height (mean ± standard deviation) of the parathyroid gland were 4.2 × 2.5 × 2.9 mm ± 1.3 × 0.8 × 1.0 mm. The density was 39.7 ± 20.6 HU on pre contrast images and 103.1 ± 47.1 HU on post contrast images, thus the organ was hypoattenuating compared to the thyroid gland on pre (166.7 ± 34.3 HU) and post contrast (234.0 ± 60.1 HU) images.

Conclusion This study offers the first description of the CT appearance of the presumed normal canine parathyroid gland. However, the overall visibility was poor.

Clinical relevance Despite the overall poor visibility of the parathyroid gland it was occasionally visible and its CT dimensions were larger as described for ultrasound in this group of dogs, which showed no clinical signs of hyperparathyroidism. Thus, visibility of the parathyroid gland on CT may not necessarily imply parathyroid disease. However, further research is necessary.

Schlüsselwörter

Hund - Glandula parathyreoidea - Computertomografie - Hyperparathyreoidismus - Schnittbildverfahren

Key words

Dog - Glandula parathyreoidea - computed tomography - hyperparathyroidism - cross sectional imaging

Publication History

Received: 13 January 2019

Accepted: 14 July 2020

Article published online:
21 October 2020

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