Multiple cartilaginous exostosis in a Golden Retriever cross-bred puppy. Clinical, radiographic and backscattered scanning microscopy findings.

Multiple cartilaginous exostosis was diagnosed in a six-month-old Golden Retriever cross-bred male with a history of forelimb lameness and isolated, but very painful, acute episodes. Physical examination revealed a right forelimb lameness with a firm, painful palpable mass on the cranial aspect of the forearm. The radiological examination showed the presence of bony masses at the humerus and radius as well as several masses in the ribs and spinous processes of the thoracic vertebrae. Based on the history and radiographic findings, multiple cartilaginous exostosis was diagnosed. Treatment with non-steroidal anti-inflammatory drugs was commenced for two weeks without any effect. Due to the lack of a response to the treatment as well as to the progressive physical deterioration of the animal, the owners requested euthanasia of the dog. Histology of the different exostoses demonstrated the presence of a hyaline cartilage cup surrounding a central area, formed mainly by bone and cartilage trabecullae. Signs of malignancy were not observed. Back-scattered scanning electron microscopy (BEI-SEM) study revealed well ordered and progressively calcified cartilage trabecullae present underneath the non-calcified cartilage cap. At a greater depth, those cartilage trabecullae became osteochondral trabecullae, and the innermost were formed exclusively by woven and lamellar bone. The histological and back-scattered electron scanning microscopy results conclude that it was a well-arranged normal endochondral ossification process that followed a centripetal pattern inside the bony mass, confirming the diagnoses of multiple cartilaginous exostoses.