Nutritional Secondary Hyperparathyroidism in the Horse

10 The Anatomy of the Parathyroid Glands in the Horse
ESTES’ (1907) description clearly established that three main types of epithelial
cells occur in the equine parathyroid, viz., chief cells, water-clear cells, and
oxyphil cells. This should be emphasized in view of the fact that even modern
textbooks and papers dealing with general parathyroid histology stress the
existence of water-clear cells and oxyphil cells as a characteristic of the human
parathyroid gland only.
LITTY (1907) distinguished two types of epithelial cells in the equine parathyroid.
In addition to the predominating light chief cells (according to modern
nomenclature), he described large cells with well-defined borders, a clear cytoplasm,
and a nucleus having variable staining properties. These cells usually
occurred in restricted areas in small groups, but in rare cases they predominated
in the microscopic field.
BOBEAU (1911) contributed a detailed description of the histology of the
equine parathyroids. He recognized four epithelial cell types, viz., light chief cells
(celldes normales) with a longitudinal diameter of 12 to 16 p and a nucleus of 5 to
7 p; water-clear cells (celhles claires) with no stainable cytoplasm (“one has the
impression of nuclei floating in an empty space”); dark oxyphil cells (cellules
sombres) with a longitudinal diameter of 10 p and deeply eosinophilic cytoplasm;
and pale oxyphil cells (grosses celldes ci prod& gramdegx ozt colloid).
BOBEAU also examined the parathyroids for fat. He stated that fat was present
in the cytoplasm of the light chief cells and, more rarely, in the dark oxyphil cells
but never in the water-clear and pale oxyphil cells. Unfortunately, BOBEAU did
not give the age of any of his horses, and the correlation between age and the
degree of fat present in the cells is therefore lacking.
VERMEULEN (1917) described two main epithelial cell types, viz., chief cells
and oxyphil cells. He also proposed a classification of the parathyroid glands
according to the amount and arrangement of connective tissue within the glands.
Fig. 3. Lower parathyroids of horses, both male and 12 years old. Parathyroid at
straight arrow, cyst at curved arrows, x 4.5.
Fig. 4. Horse, female, 22 years old. Relative size of parathyroid glands. Left part
of figure: upper gland; right part: lower gland, x 5.
Fig. 5. Horse, female, 17 years old. Typical structure of parathyroid gland. Thin
connective tissue septa subdividing gland into fine lobuli. Rich vascularization.
Mainly light chief cells. H & E, x 275.
Fig. 6. Horse, male, 1 year old. Relatively abundant stroma in parathyroid gland.
Numerous KURSTEINER’S canals (straight arrow) and cysts (curved arrows) at
hilus. H & E, x 22.5.
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