History
A 6-month-old female Mastiff was referred for evaluation of a firm mass on the head. The mass was first noticed when the dog was 4 months old. No history of trauma was associated with the appearance of the mass. The mass was initially thought to be a hematoma because the referring veterinarian drained red fluid from it. However, the size of the mass continued to increase and it was firmly attached to the dog's skull.
On physical examination, a firm mass (approx 5 to 6 cm in diameter) was detected. The mass was centered on the frontal bone dorsal to the orbits. Palpation of the mass did not elicit signs of pain, and no other abnormalities were detected. Radiographs of the skull were obtained during anesthesia (Figure 1).
Right lateral (A) and rostrocaudal (B) radiographic views of the skull of a 6-month-old Mastiff referred for evaluation of a firm mass on its head.
Citation: Journal of the American Veterinary Medical Association 229, 2; 10.2460/javma.229.2.211
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page
Radiographic Findings and Interpretation
Smooth, homogeneous periosteal new bone formation extends dorsally from the center of the frontal and parietal bones (Figure 2). The periosteal reaction is broadly based and irregularly shaped without evidence of adjacent cortical lysis or ventral extension into the cranial cavity. These findings are compatible with a nonaggressive bone lesion; idiopathic calvarial hyperostosis (ICH), osteoma, and subperiosteal hemorrhage with reactive periostitis secondary to trauma were considered as differential diagnoses. The history, clinical signs, and radiographic findings were most consistent with ICH.
Same radiographic views as in Figure 1 (enlarged). Smooth periosteal new bone formation extends dorsally from the frontal bone and rostral aspect of the parietal bone (arrows). The soft tissue is mildly thick, which is associated with the new bone formation. The periosteal reaction does not extend into the cranial cavity, and there is no evidence of bone lysis. Tubing (arrowheads) used to secure the endotracheal tube is evident.
Citation: Journal of the American Veterinary Medical Association 229, 2; 10.2460/javma.229.2.211
Comments
Histologic examination of a Jamshidi-needle biopsy specimen of the mass revealed marked periosteal woven bone formation with remodeling of underlying cortical bone and numerous irregular cement lines, features that would be unusual in chronic trauma. Thus, the benign microscopic appearance of the biopsy specimen was consistent with ICH, also known as calvarial hyperostosis syndrome. Idiopathic calvarial hyperostosis is a non-neoplastic proliferative disease of the flat bones that has been reported most commonly in young male Bullmastiffs,1,2 although it has also been reported in female Bullmastiffs.3
Depending on the stage of the disease, inflammatory microscopic features can be identified. Idiopathic calvarial hyperostosis is clinically and histologically similar to craniomandibular osteopathy in dogs and infantile cortical hyperostosis in humans, which are self-limiting diseases in young patients. Idiopathic calvarial hyperostosis is unique in its location on the skull and its breed predilection. Dogs in which ICH has been diagnosed generally have clinical signs by approximately 6 months of age.1,2
Radiographically, new bone formation is localized to the periosteum. A rostrocaudal radiographic view of the skull can be used to detect dorsal extension of the periosteal reaction on the frontal bone without ventral extension or lysis of the cranial cavity. Rostrocaudal radiographic views of the skull are indicated in the evaluation of frontal bone and sinus diseases (eg, frontal sinusitis and lysis of bone). For this radiographic view, the patient is positioned in dorsal recumbency with its nose pointed toward the ceiling. The vertically oriented x-ray beam is collimated dorsal to the nasal cavity and centered on the frontal bone.4 The collimator light should cast a shadow of the protruding area of interest. Because of the care needed to achieve accurate positioning, general anesthesia is often required for all radiographic views of the skull.5 Computed tomography can be used to evaluate abnormalities of the skull and is preferred over magnetic resonance imaging for detection of bone abnormalities such as hyperostosis. Computed tomography was used to further characterize the periosteal reaction in the dog of this report, but results of computed tomography did not change the diagnosis.
Most cases of ICH are self limiting and the lesion decreases in size once the dog reaches skeletal maturity. Some dogs have concurrent fever, lameness, and lymphadenopathy.1,2 Except for the visible mass, the dog of this report had no other clinical signs. Eight months after the initial evaluation, the owner reported that the size of the mass had decreased approximately 80%. The underlying etiopathogenesis of ICH is not known but may involve genetic, metabolic, nutritional, and infectious disorders. Histologic examination of a bone biopsy specimen is recommended to definitively diagnose and document the disorder. Presently, specific treatment is not recommended.2
- 1.
Muir P, Dubielzig RR & Johnson KA, et al. Hypertrophic osteodystrophy and calvarial hyperostosis. Compend Contin Educ Pract Vet 1996;18:143–150.
- 2.↑
Pastor KF, Boulay JP & Schelling SH, et al. Idiopathic hyperostosis of the calvaria in five young bullmastiffs. J Am Anim Hosp Assoc 2000;36:439–445.
- 3.↑
McConnell JF, Hayes A & Platt SR, et al. Calvarial hyperostosis syndrome in two bullmastiffs. Vet Radiol Ultrasound 2006;47:72–77.
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Owens JM, Biery DN. Skull. In: Radiographic interpretation for the small animal clinician. 2nd ed. Baltimore: The Williams & Wilkins Co, 1999;105–126.
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Dennis R, Kirberger RM & Wrigley RH, et al. Handbook of small animal radiological differential diagnosis. London: WB Saunders Co, , 2001;65–67.
