JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1712510): Dog
HISTOPATHOLOGIC DESCRIPTION: Bone, mandible (per contributor): Diffusely the mandible is markedly thickened by a subperiosteal / endosteal proliferation of trabecular bone and the periosteum is thickened by a 1 to 5 mm thick band of dense, fibrous connective tissue (fibrosis) that obscures the cortex. Secondary to the bone proliferation there is an undulant appearance to the bone surface. Subperiosteal trabeculae are arranged perpendicular to the periosteum, are composed primarily of woven bone interspersed with rare areas of lamellar bone, are often moderately increased in thickness (osteosclerosis), and are often widely separated by variably dense areas of fibrosis. Trabeculae contain many resting and reversal lines and are often lined by many osteoblasts and fewer osteoclasts within Howship’s lacunae (remodeling). Within a focally extensive area, numerous neutrophils and admixed hemorrhage surround fragmented, subperiosteal trabeculae and extend into the adjacent fibrous connective tissue. Multifocally, atrophic skeletal myofibers are entrapped within the overlying band of fibrosis.
MORPHOLOGIC DIAGNOSIS: Bone, mandible (per contributor): Subperiosteal new bone growth, diffuse, moderate, with acute neutrophilic osteitis, multifocal osteosclerosis, marked periosteal fibrosis and skeletal muscle atrophy, breed unspecified, canine.
CONDITION: Craniomandibular osteopathy
SYNONYM: Lion jaw
- Craniomandibular osteopathy is a bilateral, generally symmetrical, nonneoplastic proliferation of periosteal new bone with intermittent and concurrent, formation and resorption that most commonly affects West Highland white, Scottish and Cairn terriers
- Primarily affects mandible, tympanic bullae, occipital and temporal bones; occasionally parietal, frontal, maxillary and lacrimal bones and rarely the appendicular skeleton
- Tympanic bullae are often severely affected
- Mandibular changes include the endosteum, periosteum and trabecular bone
- Initial presentation at 4 to 7 months of age
- Pathogenesis is unknown, but likely multifactorial
- Infectious etiology is suggested by the presence of inflammatory infiltrates; no agent has been identified
- Prevalence in certain breeds implies a genetic basis; autosomal recessive inheritance is suggested in West Highland white and Scottish terriers
- Has been associated with a leukocyte adhesion molecule deficiency in a colony of Irish setter puppies with concurrent metaphyseal osteopathy
- Intermittent and progressive; self-limiting (lasting many weeks to a few months); may completely recede and is nonfatal
- Growth plates are not involved; resolution corresponds with their closure
- Extensive ossification of the soft tissues surrounding the mandibular angular process may result in an inability to eat and necessitate euthanasia
TYPICAL CLINICAL FINDINGS:
- Painful and difficult mastication
- Mandibular pain and swelling
TYPICAL GROSS FINDINGS:
- Bilaterally symmetrical, extensive proliferation of bone; rarely asymmetric or unilateral
- Bone is thickened through the width and length of the mandible; greatest changes occur at angular process
- Ossification of soft tissues
- Atrophy of mastication muscles
- Tympanic bullae are filled with bone and often enlarged up to 2-4 times normal
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Changes in the endosteum and trabecular bone characterized by both bone resorption and formation and consists of many reversal cement and resting lines within bony trabeculae
- Medullary spaces contain irregular, sclerotic trabeculae of woven bone often oriented perpendicular to cortex, separated by fibrous connective tissue which may fill marrow spaces
- The periosteum may also be thickened by fibrous connective tissue
- Random, disoriented osteoclastic resorption involving lamellar and woven bone with production of abundant coarsely woven bone
- Increased osteoblastic activity on trabecular surfaces
- Lymphocytes, plasma cells, and neutrophils often present in areas of remodeling and ossification
- Rarely osteonecrosis
- Resolution of the disease involves replacement of woven trabeculae with lamellar bone and gradual resorption
ADDITIONAL DIAGNOSTIC TESTS:
- Radiology: Generally symmetrical enlargement of mandibles and tympanic bullae
- Calvarial hyperostosis syndrome: Progressive, self limiting, asymmetrical thickening of calvaria; mandibles not involved; affects young (less than 1 year), male Bullmastiffs
- Metabolic: Renal and nutritional secondary hyperparathyroidism (fibrous osteodystrophy)
- Neoplastic bone disease
- Dissecting periostitis
- Infantile cortical hyperostosis (Caffey-Silverman syndrome): Bilateral proliferative bone disease of infants affecting the mandible
- Paget"s disease: Similar mosaic pattern of resting and reversal lines; paramyxoviral infection suggested as the etiology
- Porcine cortical hyperostosis: Primarily affects long bones in young animals
- Hypertrophic osteopathy (hypertrophic pulmonary osteopathy): Diffuse periosteal new bone formation most often in the distal radius, ulna, tibia, metacarpals or metatarsals associated with inflammation or neoplasia in the thorax
- Canine hepatozoonosis ( americanum) may cause a similar lesion to hypertrophic osteopathy but generally occurs more proximal on the limb
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- Pastor KF, Boulay JP, Schelling SH, Carpenter JL. Idiopathic hyperostosis of the calvaria in five young bullmastiffs. J Am Anim Hosp Assoc. 2000; 36(5):439-445.
- Thornburg LP. Infantile cortical hyperostosis (Caffey-Silverman syndrome). Animal model: Craniomandibular osteopathy in the canine. Am J Pathol. 1979; 95(2):575-578.
- Olson EJ, Carlson CS. Bones, joints, tendons, and ligaments. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017: 1006, 1261.
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