Nutritional Secondary Hyperparathyroidism in the Horse

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4 ‘The Anatomy of the Parathyroid Glands in the Horse thyroid, whereas parathyroid IV is usually located dorsomedially in the midsection of the thyroid. The literature on the embryology of the pharyngeal area in the horse is limited. The papers by EWART (1915) and ROBINSON and GIBSON (1915) do not specifically concern the parathyroids. Both papers, however, mention that in the horse the third pharyngeal pouch is much larger than the fourth. HARRISON and MOHN (1932) studied two horse embryos, 13 and 18 mm. in length. Parathyroid primordia were not observed in the smaller embryo. In the 18 mm. stage only one pair of parathyroids was identified, but the authors left the question of their derivation open. As will be described below, cysts occur very frequently around and within the equine parathyroid glands. GILMOUR (1937), in his description of the embryology of the pharyngeal pouches in man wrote: “They are rudimentary and of no apparent function but are important in that they persist into adult life and must be recognized if cystic structures in the neighbourhood of the parathyroids after birth are to be interpreted correctly.” The embryologic background of these cysts was first described by ~(URSTEINER (1899). He showed that a communicating segment between thymus I11 and parathyroid I11 exists in all embryos. He referred to this as “gland canals” and “gland vesicles” (Driisenkade and Driiserzbla.rcben). In the human embryo these canals are best developed at the 20 cm. stage andusuallydisappear at the 30 cm. stage. In the newborn they are present at the hilus of the parathyroid gland only occasionally. They appear only in relation to parathyroid 111. ~(URSTEINER hypothesized that these canals, now usually associated with his name, may undergo cystic dilation and that they actually are responsible for congenital cysts in the upper cervical region. GILMOUR (1937) further studied these embryonic rudiments and recognized three types of canalicular, vesicular, or glandlike structures. Type I consists of small, solid, cellular buds originating from the parathyroid before the separation of thymus I11 and parathyroid 111. A lumen may occur in the bud and a vesicle is thus formed. GILMOUR’S type 2 is a glandlike alveolus with a small lumen surrounded by cubical cells believed to be derivatives of the thymus or its cord. Type 3 consists of larger vesicles or canals lined by flat cells. They were shown to be of thymic or thymus cord origin. Any one of the three types may persist into adult life. In agreement with KUR- STEINER, GILMOUK stated that these rudiments appear in relation to parathyroid I11 only. Downloaded from vet.sagepub.com by guest on April 14, 2010
Comparative Aspects of the Embryology of the Equine Parathyroids 5 Embryonic rudiments in the equine parathyroid glands have been given little attention in the literature. ESTES (1907), in his series of 125 parathyroids, observed cysts at the hilus in 18 cases (14%). The cysts were usually lobulated “as if several cysts were attached at a common origin”. ESTES further wrote : “Microscopically it is seen that the capsule of the parathyroid runs over the cyst and forms its capsule also. In this capsule one sometimes finds masses of what is apparently thymus tissue, raising the question as to whether the cysts may possibly have originated from the thymus rather than the parathyroid.” No cysts were found “in the parathyroid substance.” LITTY (1907) described the parathyroid glands of 12 normal horses without cysts and 2 cases with such cysts, which he classified as cystic degeneration. 2. The Macroscopic Anatomy of the Equine Parathyroid Glands a) Review of the Literatwe SANus,rnoM (1880) dcscribcd om pair of parathyroid glaiids locatcd at thc anterior dorsolateral aspect of the thyroid artery. Es~es (1907) confirmed this pair and stated that the horsc has two pairs of parathyroid glands. After serial sectioning of the thyroid glands, ESTES claimcd to havc demonstratcd parathyroids within 13 out of 25 thyroids. “They seem to bc distributed irregularly in the thyroid tissue, occurritig often iicar the superior pole in a rather superficial position but are sometimes dccplp cmbedded.” VT:RMEULEN (1917) stated that parathyroids I11 and IV reverse in thc horse, but he prescnted no embryologic evidence for his views. He callcd the larger, external gland parathyroid IV and further stated that in the horsc “all parathyroids arc always or in the majority of the cascs located externally.” In the work by Es.Ir.s and by VCRIVIHJLHN thc terms “cxtcrnally” aiid “internally” werc used to indicate the relationship to the thyroid gland rather than the cmbryologic origin. The discussion on the number of parathyroid glands in the horse was brought to an end by HAsIIIMwro and I
Page 1 and 2: Pathologia Veterinaria Online http:
Page 3 and 4: Supplementum ad Vol. 1 (1964) Patho
Page 5 and 6: V . Experimental Nritritional Secon
Page 7 and 8: Introduction and Object of Investig
Page 9: I. The Anatomy of the Parathyroid G
Page 13 and 14: The Aracroscopic Anatomy of the Equ
Page 15 and 16: The Microscopic Anatomy of the Equi
Page 17 and 18: 'I'hc hlicroscopic Anatomy of the E
Page 19 and 20: ’The I\licroscopic Anatomy of the
Page 21 and 22: 10 . 9 . a . 7 0 + 6 . 5 . 0 ’I
Page 23 and 24: ‘The hl icroscopic Anatomy of the
Page 25 and 26: ’I’hc hlicroscopic Anatomy of t
Page 27 and 28: ‘I’lic ihlrcroscopic Anatomy of
Page 29 and 30: ‘I’hc Alicroscopic Anatomy of t
Page 31 and 32: Discussion 25 7bbic 1 .. Avcragc si
Page 33 and 34: Discussion 27 Table VZZ. Nuclear si
Page 35 and 36: 11. Nutritional Secondary Hyperpara
Page 37 and 38: The Nature of the Osteopathy 31 Fig
Page 39 and 40: ’The Nature of the Osteopathy 33
Page 41 and 42: Etiology 35 Experiments and clinica
Page 43 and 44: Clinical Pathology 37 Table X. Seru
Page 45 and 46: 111. Experimental Nutritional Secon
Page 47 and 48: Ration 41 Table XI/. Calcium and ph
Page 49 and 50: Necrops y 43 6. Necropsy The animal
Page 51 and 52: Clinical Observations 45 During wee
Page 53 and 54: Clinico-pathologic Determinations 4
Page 55 and 56: 90. *. 90. 90. 70. / . Clinico-path
Page 57 and 58: (:linico-pathologic Determinations
Page 59 and 60: Rocntgencilogic Observations 53 Fie
Page 61 and 62:
lioentgcnologic Ohscrvntions 55 I,'
Page 63 and 64:
Pathologic Anatomy 57 7bb/e XIS. Si
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Pathologic Anatomy 59 fhb/c. A’X.
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Pathologic Anatoiny Downloaded from
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Pathologic Anatomy 67 Downloaded fr
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Pathologic Anatomy 69 Fiq. 37. Cont
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V. Experimental Nutritional Seconda
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Scruin Phosphorus, Calciiiiii, and
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Serum Phosphorus, Calcium, and Alka
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Serum Phosphorus, Calcium, and Alka
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The Parathyroid Glands 79 should be
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The Skeleton 81 5. The Skeleton The
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The Skeleton 83 ary hyperparathyroi
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Summary and Conclusions The thesis
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Siimmary and Conclusions 87 Rocntgc
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References 89 COILIP, J. B.: 'I'hc
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Refereiices 91 ~~CILAN, F. C. and U
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Appendix Tables and Statistical Ana
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Tables and Statistical Analyses 95
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’Tablcs and Statistical Analyscs
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Nutritional Secondary Hyperparathyroidism in the Horse

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