Caudal Fossa Respiratory Epithelial Cyst in a Dog: Clinical, Magnetic Resonance Imaging, and Histopathologic Findings

An 11-month-old female Bloodhound was presented because of progressive ataxia and head swaying with insidious onset 2 weeks before admission. On neurologic examination, the dog was bright, alert, and responsive, but showed involuntary swaying of the head to both sides and a mild head tilt to the left. Gait inspection disclosed mild ataxia. Paw placing responses were delayed in all 4 limbs. Segmental spinal reflexes and skin sensation were normal. Cranial nerve examination identified left-sided ventrolateral strabismus. Nystagmus was not seen. All other cranial nerve functions were normal. Based on the clinical findings, bilateral central vestibular disease was suspected. Hematology and serum biochemistry findings were within normal reference ranges. For magnetic resonance imaging (MRI), the dog was premedicated with diazepam (0.5 mg/kg IV) and alfaxolone (2 mg/kg IV). Anesthesia was maintained with isoflurane. MRI was performed at the MRB using a 1.5 Tesla Siemens Magnetom Avanto and 2 purpose-built CPC coils. Magnetic resonance imaging of the brain disclosed a well-circumscribed cystic lesion with dimensions of approximately 1.5 9 2.2 9 2.9 cm inside of the fourth ventricle, with dorsal displacement of the cerebellum, which was pushed against the osseous tentorium cerebelli, and dorsal compression of the myelencephalon (Fig 1). Both structures were decreased by >50% of their expected dorsoventral diameters (Fig 1A). Sagittal images indicated no signs of foramen magnum herniation or cervical syringomyelia (Fig 1A,B). On close examination, the cyst appeared loculated with a large dorsomedial compartment being strongly hyperintense on T2-weighted images (T2W; Fig 1C) and on fluid-attenuated inversion recovery (FLAIR) sequence (Fig 1D). Another, smaller ventrolateral compartment was hyperintense on T2W (Fig 1C asterisk) and isointense to brain parenchyma on FLAIR images (Fig 1D asterisk). The entire lesion was hypointense on precontrast T1-weighted images (T1W; Fig 1A) with slightly more extensive signal void in the smaller ventrolateral compartment. After injection of a single bolus of gadopentetate dimeglumine (Magnograf, 0.2 mmol/kg IV), a peripheral ring enhancement with clear demarcation from neighboring neuroparenchyma and the ventricular lumen was seen (Fig 1B arrows). The rostral parts of the ventricular system were symmetrically enlarged. Based on the imaging findings, an intraventricular cyst was diagnosed. The authors considered an epidermoid/dermoid cyst (IEDC) most likely. Additional differential diagnoses included choroid plexus cyst, ependymal cyst, and abscess bulging into the ventricle. Upon careful risk evaluation, the dog underwent brain surgery. The dog received cefazolin (20 mg/kg IV) before surgery. Premedication, induction, and maintenance of anesthesia were performed as described above. In addition, fentanyl was given as a continuous rate infusion (CRI) (0.002 mg/kg/h). Just after craniotomy, the dog received methylprednisolone (30 mg/kg IV) and mannitol (1 g/kg IV) as a CRI over 20 minutes. To prevent possible mannitol rebound effect, the dog received an injection of furosemide (2 mg/kg IV) 30 minutes after the CRI. Perioperative monitoring included continuous assessment of cardiorespiratory function by pulse oximetry, electrocardiography, and expired gas analysis. The caudal fossa was approached through a central suboccipital craniotomy. After durotomy, a cyst was identified within the fourth ventricle, confined by an opaque, yellowish-white capsule. The cyst wall was incised, after which approximately 6 mL of yellowish-brown mucoid fluid was removed with a syringe. The cyst then was removed in total by blunt From the Section of Clinical & Comparative Neuropathology, Institute of Veterinary Pathology, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University Munich, Munich, (Molin, Matiasek); and the Neurology Referral Service, Dettelbach, Germany (Rentmeister). Corresponding author: K. Matiasek, Section of Clinical & Comparative Neuropathology, Centre for Clinical Veterinary Medicine, Ludwig Maximilians University of Munich, Veterinarstr. 13, D-80539 Munich, Germany; e-mail: Kaspar.matiasek@neuropat hologie.de. Submitted February 26, 2014; Revised March 13, 2014; Accepted March 25, 2014. Copyright © 2014 by the American College of Veterinary Internal Medicine DOI: 10.1111/jvim.12369 Abbreviations: