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Compendium March 2009 (Vol 31, No 3)

Clinical Snapshot (March 2009)

by Georgina Barone, DVM, DACVIM (Neurology)

    Case Presentation

    A 9-year-old, 11.2-lb (5.1-kg), spayed Pekinese presented with an acute onset of collapse and apparent obtundation. The history included a laminectomy (T13–L1) several years prior, from which the dog had recovered uneventfully. However, in the month before presentation, the owner had reported a recurrence of back pain, for which baby aspirin (unknown dose and quantity) was being administered. The owner had noted no other abnormalities before the acute collapse and stated that there was no possibility of toxin exposure.

    Abnormalities noted on the initia lexamination included hyphema and miosis in the right eye. The remainder of the general physical examination was unremarkable. On neurologic examination, the patient was dull and minimally responsive with a left head tilt. An intermittent opisthotonic posture was noted. The menace response was absent in both eyes, and there was a resting vertical nystagmus along  with a ventrolateral strabismus in the right eye. Postural responses were absent in all four limbs, and the dog was tetraparetic and nonambulatory, although voluntary motor activity was present in all four limbs.

    A complete blood count revealed a mature neutrophilia, hemoconcentration (hematocrit: 67.7%), and mild thrombocytopenia with a platelet count of 156 × 103/μL (reference range: 175 × 103 to 500 × 103/μL). Results of a serum chemistry panel were unremarkable. In-house prothrombin time was prolonged at 52 seconds (reference range: 12 to 17 sec). Images obtained with abdominal ultrasonography and thoracic radiography were unremarkable. Magnetic resonance imaging of the brain was conducted using a 3.0-tesla Philips Achieva magnet. T1- T2-weighted (Figures A and B), T1 postcontrast (gadolinium), and fluid-attenuated inversion-recovery (FLAIR; Figure C) images were obtained.

    1. What is your anatomic diagnosis?
    2. What is your diagnosis based on the MRI abnormality?
    3. Are additional diagnostics indicated?
    4. What is this dog's prognosis?

    Answers and Explanations

    1. The presence of opisthotonos implies a lesion in the caudal fossa and may be seen with abnormalities of the rostral cerebellum. It is often observed when intracranial pressure is increased. The head tilt, vertical nystagmus, and postural deficits are suggestive of a central vestibular problem. Changes in mental status are often seen with prosencephalic disease but may also be observed when lesions in the brainstem impair the ascending reticular activating system. In this case, the miosis in the right eye was attributed to uveitis associated with hyphema.

    2. Hemorrhagic infarct in the left cerebellar hemisphere and nuclei. There is severe associated edema with a mass effect compressing the brainstem on the left. This was presumed to be the reason why this patient displayed medullary signs despite the primary lesion being confined to the cerebellum.

    The appearance of hemorrhage in the central nervous system (CNS) depends on chronicity. In the acute stages, such as with this patient, the presence of deoxyhemoglobin results in hypointensity on T2-weighted images and isointensity to hypointensity on T1-weighted images.1 The sharp line of demarcation between normal and abnormal tissues, the wedge shape, and the hyperintensity of lesions on FLAIR images strongly support the diagnosis of a vascular accident. The hypointense center of the lesion in Figure C is likely due to the presence of deoxyhemoglobin from hemorrhage within this large infarction. It is surrounded by a relatively large area of hyperintensity that demarcates the full extent of the infarction.

    3. With the high index of suspicion for coagulopathy in this patient, further tests such as a full coagulation profile (prothrombin time, partial thromboplastin time, fibrinogen, D-dimer, and PIVKA [proteins induced by vitamin K antagonism]) were recommended, but the owner declined. In this case, the hemorrhage was suspected to be secondary to chronic aspirin administration.

    4. The prognosis for recovery after CNS infarction is highly variable and depends on whether there are underlying medical conditions that predispose the patient to recurrent CNS infarction (as opposed to patients with spontaneous or idiopathic nonhemorrhagic stroke).2 Infarctions can be classified as territorial, lacunar, and watershed.2 Territorial infarcts result from compromise of one of the main arteries of the brain, whereas lacunar infarcts result from compromise of an intraparenchymal superficial or deep artery. Watershed infarctions arise in the interface between large arteries.2 The infarction type does not necessarily influence outcome, but in human patients, infarct size and location are prognostic indicators; similar results have not beenfound in veterinary medicine.3

    In my experience, the severity of the initial clinical signs and the ability to accurately diagnose and treat underlying causes are the most important prognostic indicators. Unfortunately, despite the administration of mannitol (1 g/kg IV) and vitamin K (2.5 mg/kg SC), this patient experienced cardiac and respiratory arrest and expired several hours after magnetic resonance imaging was conducted.

    Downloadable PDF

    1. Bagley RS. Bleeding into the central nervous system. Proc 18th ACVIM Forum 2000:334-335.

    2. Garosi L, McConnell J, Platt SR, et al. Results of diagnostic investigations and long-term outcome in 33 dogs with brain infarction (2000-2004). J Vet InternMed 2005;19(5):725-731.

    3. Thomas WB. Cerebrovascular disease. Vet Clin North Am Small Anim Pract 1996;26:925-943.

    References »

    NEXT: Disclosing Medical Errors: Restoring Client Trust

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