Prevalence and Clinicopathologic Features of Canine Metastatic Melanoma Involving the Central Nervous System: A Retrospective Analysis and Comparative Review

Relative Tumour Volume in Canine Oral Melanoma Staging and Prognosis

Melanoma is one of the most common canine oral malignant tumours and is highly aggressive and metastatic, even at the early stages of development. Surgery relies on wide excision of the primary tumour and regional lymphadenectomy, with or without adjuvant therapy. Tumour location and size are important when considering staging, which ultimately affects the curative intent of surgery. Nevertheless, absolute tumour volume (TV) is not related to the vast phenotypic variability within canine breeds. This study aimed to determine the cutoff values of two ratios-tumour-to-head volume (THR) and tumour-to-body volume (TBR)-and assess whether they could be associated with the odds of finding metastasis at presentation and/or the likelihood of achieving tumour-free excision margins. A retrospective case series involving 51 dogs was used to evaluate the preoperative head/neck and chest computed tomography and histopathology of the primary mass and excised lymph nodes. Higher TV, THR% and TBR% values were associated with bone lysis and mitotic count (MC). The Ki67 index was significantly associated with local and distant metastases at presentation, whereas MC was associated with local metastasis alone. Tumour-infiltrated surgical margins were associated with caudally located tumours, regardless of the tumour size. Dogs with lymph node metastasis at presentation were seven times more prone to have local relapse. TV, THR% and TBR% values were positively associated with local lymph node metastasis at presentation. Cutoff values for both TV and TBR% were proposed to predict lymph node metastasis at presentation (TV = 6.423 cm3 and TBR% = 0.043), being supported by post-surgical survival analysis.

Case report: MRI and CT imaging features of a melanocytic tumour affecting a cervical vertebra in an adult dog, and review of differential diagnosis for T1W-hyperintense lesions

A 7-year-old Lhasa Apso presented with a history of left thoracic limb lameness and neck pain. Magnetic resonance imaging revealed a well-defined, extradural lesion that was hyperintense on T1-weighted (T1W) images and isointense on T2-weighted (T2W) images and T2* images located at the left lamina of the C4 vertebra. Computed tomography showed an isoattenuating and contrast-enhancing mass centered on the left C4 vertebral lamina with associated osteolysis. The mass was surgically debulked, and histopathology revealed a malignant melanocytic tumour. The patient recovered completely and received radiotherapy and three doses of the melanoma vaccine as adjunctive treatment. Eighteen months following treatment, the patient presented with neck pain again, but further investigations were declined at this stage, and the patient was euthanised. To the author's knowledge, this is the first case report describing the imaging characteristics of a cervical extradural melanocytic tumour in a dog. This case illustrates the MRI and CT imaging features and treatment of a canine melanocytic tumour of the cervical vertebrae.

Diagnostic immunohistochemistry of primary and secondary central nervous system neoplasms of dogs and cats

The diagnosis of primary and secondary CNS neoplasms of dogs and cats relies on histologic examination of autopsy or biopsy samples. In addition, many neoplasms must be further characterized by immunohistochemistry (IHC) for a more refined diagnosis in specific cases. Given the many investigations assessing the diagnostic and prognostic IHC profile of CNS neoplasms in the veterinary literature, it may be difficult for the diagnostic pathologist or pathology trainee to narrow the list of reliable diagnostic IHCs when facing a challenging case. Here we compile a comprehensive list of the most diagnostically relevant immunomarkers that should be utilized for the diagnostic support or confirmation of the most common primary and secondary CNS neoplasms of dogs and cats.

Metastatic extradural melanoma of the lumbar spine in a cat

A 7-year-old neutered male Domestic shorthair cat, with a 1.5-year history of left eye enucleation secondary to a diffuse iris malignant melanoma, was evaluated for progressive onset of pelvic limb paresis and ataxia with severe thoracolumbar hyperaesthesia and dysorexia. Neurological examination localised a lesion to the T3-L3 spinal cord segments. Magnetic resonance imaging of the thoracolumbar spine showed a well-defined extradural T1-weighted hyperintense non-contrast-enhancing mass, initially suggesting a potential haemorrhagic component. Exploratory surgery revealed a brownish extradural lumbar mass. Histologic examination concluded to a melanoma, most probably metastatic given the animal's previous medical history. This report highlights the importance of collecting a complete medical history, which can help in obtaining a preliminary differential diagnosis in cats with clinical signs of myelopathy. Although the location of this metastasis is particularly unusual both in human and veterinary medicine, making optimal treatment challenging for neurosurgeon, our increased understanding of immune and tumour cell biology during the past decade is likely to improve the future treatments of feline melanoma and its metastases.