Case 2 180720-2 (99N0815)
Conference Coordinator: Dr Sarah Stevens.
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3-day-old alpine neonate goat kid.
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The long bones have increased metaphyseal trabecular bone. The vertebrae are composed mainly of cartilage with small central cores of bone.
This (demineralized) section of long bone extends from articular surface through the physis and into approximately one third of the diaphysis. There is a conical core of unremodeled primary spongiosa, which fills the medullary cavity into the diaphysis. The primary spongiosa has retention of cartilage cores. The cortex lacks compaction and instead is composed of moderately thick anastomosing trabeculae of bone forming. There is a paucity of osteoclasts.
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Lone bone: osteopetrosis
Osteopetrosis is a rare bone disease characterized by defective osteoclastic resorption resulting in accumulation of primary spongiosa within the marrow cavities. Conference discussion touched on a number of topics related to osteopetrosis. Many individuals commented on the challenge of picking out the abnormalities, especially without an age-matched control and without knowing the age of this individual animal.
There was also discussion regarding the role and presence of osteoclasts in this disease. In this case, it was sometimes challenging to differentiate between osteoclasts and megakaryocytes, however, it was noted there was a paucity of osteoclasts in this tissue. However, it is important to note that that is not always the case. Even though the pathogenesis is due to osteoclast dysfunction, they may still be present and potentially in increased numbers, but as they are defective that is the cause of the retained primary spongiosa. Gross examination is often very helpful in making this diagnosis or as a clue that further evaluation of the bone is necessary. Sectioned long bones have a conical core of unremodeled primary spongiosa filling the medullary cavity which is grossly evident and is characteristic (pathognomonic) for this lesion. Lastly, the point was made that despite the dense appearance, these bones actually have increased fragilityLinden E. Craig, K. E. Dittmer, Keith G. Thompson. Bones and Joints. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol. 1, 6th ed. Philadelphia, PA: Elsevier; 2016:50–53.
