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Proximal radial bone cyst in a two year-old Chihuahua.
Elbow Elbow Lateral Neutral Lateral Initial
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Elbow Elbow Lateral Neutral Post Op

Bone cysts are benign lesions of metaphyseal bone.

History and diagnosis.

This patient presented with persistent forelimb lameness with pain localising to the elbow. Radiographs revealed a proximal radial cyst which was evaluated via out-patient CT. The radiographic features suggested an aneurysmal or unicameral bone cyst but neoplastic processes such as osteoclastoma and chondrosacroma could not be excluded.

Aneurysmal bone cysts are expansile osteolytic bone lesions comprised of large vascular sinusoids divided into blood-filled cavities by connective tissue septa that can manifest clinically as non-weight-bearing lameness, pain and swelling

Treatment.

Expansion cysts continue to enlarge if not treated. Reported treatments include surgical curettage and placement of bone graft (Banhart 2003, Worth. et al 2007) to arrest further cyst expansion. The use of polymethylmethacrylate (PMMA or 'bone cement') is also a reported treatment technique in humans (Sarierler 2004).

Surgical management.

A surgical approach was made to the caudo-lateral aspect of the proximal radius where the cortical bone has been identified on the CT as being thinnest. A small fenestration was cut into the cyst using an oscillating saw to allow a curette to be introduced and the internal cyst lining was removed.

A cancellous autograft was harvested from the proximal humerus of the ipsilateral limb and this was mixed with cancellous allograft (DBM; Veterinary Tissue Bank) to achieve a volume of graft suitable to fill the lesion. This graft was packed into the lesion and soft tissues closed routinely afterwards. The small bone section removed during fenestration was submitted for histopathology.

Outcome.

The patient made a routine recovery and made a gradual improvement in limb function. Post operative radiographs at six weeks showed no further cyst expansion and osseous conversion of the cyst lumen.

References:

Barnhart, MD (2002), 'Malignant transformation of an aneurysmal bone cyst in a dog', Veterinary Surgery: 31 - (6), pp. 519-524,

Benamou, J, Lussier, B, Alexander, K, Gains, M, & Savard, C n.d., 'Use of magnetic resonance imaging and histopathologic findings for diagnosis of an aneurysmal bone cyst in the scapula of a cat', Javma-Journal Of The American Veterinary Medical Association, 240, 1, pp. 69-74, Science Citation Index, EBSCOhost, viewed 17 November 2017.

Sarierler M, Cullu E, Yurekli Y, Birincioglu S (2004): Bone cement treatment for aneurysmal bone cyst in a dog. Journal of Veterinary Medical Science 66, 1137–1142.

VIGNOLI, M, STEHLIK, L, TERRAGNI, R, CAVALLO, L, & PROKS, P 2015, 'Computed tomography-guided cementoplasty combined with radiation therapy for an aneurysmal bone cyst in a dog: a case report', Veterinární Medicína, 60, 2, pp. 109-114, Academic Search Complete, EBSCOhost, viewed 17 November 2017.

Worth AJ, Thompson KG, Owen MC, Mucalo MR & Firth EC (2007)
Combined xeno/auto-grafting of a benign osteolytic lesion in a dog, using a novel bovine cancellous bone biomaterial, New Zealand Veterinary Journal, 55 (3), 143-148,