Histiocytic sarcomas are characterized by proliferation and/or infiltration of neoplastic histiocytes localized to specific organs, unlike malignant histiocytosis which involves many organ systems. Only a few cranial histiocytic sarcomas have been reported. Here we describe four dogs that presented with neurological deficits referable to the forebrain, and were diagnosed histologically as having histiocytic sarcoma. Using magnetic resonance (MR) imaging, the tumors were characterized by a T2-hyperintense and T1-isointense mass in one dog, T2- and T1-isointense extraaxial masses in two dogs, and a diffuse T2-hyperintense lesion over the left cerebral cortex in one dog. All tumors had contrast enhancement. MRI features in three of the four dogs were similar to that of meningioma, supported by the observation of a dural tail in two of these three dogs, and a broad base of attachment in the other. In the other dog the imaging findings were similar to those of encephalitis. Intracranial histiocytic sarcoma does not appear to have specific MR imaging features and can be confused with meningioma or encephalitis.

ABSTRACT. Fibrocartilaginous embolism (FCE) is a disorder of acute onset that presents with nonprogressive ataxia. We performed a retrospective examination of FCE of the spinal cord diagnosed by characteristic clinical findings and magnetic resonance imaging (MRI) in 26 dogs. In the present study, treatment consisting of physiotherapy alone, or this in combination with corticosteroid administration, was initiated immediately following diagnosis of FCE. Age at onset and the gender ratio in the present study closely correlated with those previously reported. In the present study, 88% of the dogs that developed FCE were small-to medium-sized, which is different from previously reported studies. There is a possibility that FCE also develops relatively frequently in small-to medium-sized dogs. No significant difference was observed between the physiotherapy alone and the physiotherapy and corticosteroids groups of dogs. FCE development has been reported predominantly at the vertebral levels C6-T2 and L4-S3 and less frequently at C1-5 and T3-L3. However, in the present study, FCE developed predominantly at T3-L3. FCE developed at T3-L3 or C1-5 in 69% of the cases in the present study, suggesting that there is relatively frequent development of FCE at these vertebral levels. The recovery time of T3-L3 was the shortest (10.2 ± 7.4 days), and that of C1-5 was next-shortest (15.8 ± 5.4) in this study. This suggested the possibility that the detection ratio of cases was low, because the symptoms in cases of FCE that has developed in C1-5 and T3-L3 would have improved before inspection in the secondary institution, where the MRI and diagnosis were performed. KEY WORDS: canine, fibrocartilaginous embolism, magnetic resonance imaging, spinal cord.

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Intradural disc herniation is a rarely reported cause of neurologic deficits in dogs and few published studies have described comparative imaging characteristics. The purpose of this retrospective cross sectional study was to describe clinical and imaging findings in a group of dogs with confirmed thoracolumbar intradural disc herniation. Included dogs were referred to one of four clinics, had acute mono/paraparesis or paraplegia, had low field magnetic resonance imaging (MRI) and/or computed tomographic myelography, and were diagnosed with thoracolumbar intradural disc herniation during surgery. Eight dogs met inclusion criteria. The prevalence of thoracolumbar intradural disc herniation amongst the total population of dogs that developed a thoracolumbar intervertebral disc herniation and that were treated with a surgical procedure was 0.5%. Five dogs were examined using low-field MRI. Lesions that were suspected to be intervertebral disc herniations were observed; however, there were no specific findings indicating that the nucleus pulposus had penetrated into the subarachnoid space or into the spinal cord parenchyma. Thus, the dogs were misdiagnosed as having a conventional intervertebral disc herniation. An intradural extramedullary disc herniation (three cases) or intramedullary disc herniation (two cases) was confirmed during surgery. By using computed tomographic myelography (CTM) for the remaining three dogs, an intradural extramedullary mass surrounded by an accumulation of contrast medium was observed and confirmed during surgery. Findings from this small sample of eight dogs indicated that CTM may be more sensitive for diagnosing canine thoracolumbar intradural disc herniation than low-field MRI.