Morphologische Grundlagen der Schilddrüsensonographie bei der Katze

Morphological fundamentals for the sonographic examination of the
feline thyroid gland The thyroid glands of 101 deceased cats were
removed for morphological, sonographical, morphometrical,
volumetrical and pathohistological assessment to investigate the
morphological fundamentals for sonographic examination. The
determined reference range extends over 0,08 – 0,27 ml in volume,
13,8 – 25,2 mm in length, 2,3 – 4,1 mm in width and 3,9 – 7,1 mm in
height of the feline thyroid gland. These parameters are
independent of body weight, age, sex and castration status of the
cat. A correction factor of 0,45 has been established from the
volumetrically and morphometrically measured values by sonographic
survey. This makes it possible to apply the ellipsoid formula for
the specific determination of the feline thyroid gland volume.
However, comparative studies have shown a remarkably broad standard
deviation for this method of calculating the thyroid gland volume
in the cat. Its assessment by surveying the thyroid gland lobes`
width and height is more expressive: the ratio should not be below
1:1,5. The number of detected thyroid alterations in the cat was
surprisingly high. Mainly - in 48 out of 101 animals - nodular
hyperplasia and adenomas have been found. Sonographic examination
revealed characteristic features of nodular hyperplasia and adenoma
cases. However, these examinations could not provide reliable
distinctive marks. In addition, two adenocarcinomas were found.
Their sonographic examination resulted in a list of characteristics
of thyroid malignancies (e.g. outstanding size, knobby surface,
inhomogeneous echostructure with poor echogenity) as reported in
literature. Analogous to the proven etiology of human nodular
hyperplasia and adenoma hypothetically the high incidence of those
alterations in cats could be caused by chronic iodine deficiency.
This hypothesis is in line with the recently detected deficitary
iodine content of an average of commercial cat food. Nodular
hyperplasia and adenoma are one of the major causes for feline
hyperthyroidism. In the recent years their incidence has increased.
The studies on hand emphasize the importance of the sonographic
examination for detection of such morphologic thyroid gland
alterations as a supplementary measure to laboratory diagnostics of
hyperthyroidism.