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Invasion of fat into the brain case in a cat
  1. D. Szabo, DVM, MRCVS1,
  2. T. C. Saveraid, DVM, DACVR2,
  3. K. Marioni-Henry, DVM, PhD, DipACVIM(Neurology), DipECVN, MRCVS1,
  4. M. A. Bush, MA, VetMB, CertSAS, MRCVS1 and
  5. S. Rodenas, DVM, DipECVN, MRCVS1
  1. 1 Southern Counties Veterinary Specialists, 6 Forest Corner Farm, Hangersley, Ringwood, Hampshire BH24 3JW
  2. 2 VetRadiologist, 1776 Wellesley Avenue, St Paul, MN 55105, USA

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FAT in the brain case has occasionally been reported in the human literature and is usually secondary to intracranial fat-containing tumours or iatrogenically caused by free fat grafts placed into skull defects following craniotomy (Tokiguchi and others 1988, Reece and others 1989, Hwang and Jackler 1996, Horsburgh 2009), it can also represent normal tissue in the cavernous sinus (Tokiguchi and others 1986). This short communication reports on the case of a six-month-old, entire, male domestic shorthair cat with fat in the cranial cavity.

The cat was presented to Southern Counties Veterinary Specialists (SCVS) for emergency evaluation following a road traffic accident. Radiographs obtained by the referring veterinarian revealed a separation of the mandibular symphysis, fractured nasal bones and a sagittal split of the left maxilla. On presentation at SCVS, physical examination revealed a prolonged capillary refill time (>2 seconds), expiratory dyspnoea, weak femoral pulses and hypothermia (35.6°C). Neurological examination revealed a stuporous mental status and non-ambulatory tetraparesis. Nasal septum sensation and menace responses were absent bilaterally, there was bilateral miosis with anisocoria, and pupillary light reflexes were absent bilaterally. On the basis of these findings, a diffuse prosencephalic lesion secondary to head injury was suspected.

Thoracic radiographs obtained on presentation revealed a mild pleural effusion. Initial emergency bloodwork was normal apart from mild anaemia (29 per cent, reference range 30 to 45 per cent).

Initial treatment included 1 g/kg mannitol (Mannitol; Fresenius Kabi) intravenously, intravenous fluid therapy with 4 ml/kg/hour Hartmann's solution (Aqupharm 11; Animalcare) and 0.5 ml/kg/ hour hydroxyethyl starch (Voluven; Fresenius Kabi), 0.1 mg/kg meloxicam (Metacam; Boehringer Ingelheim) subcutaneously, 22 mg/kg clavulanate-potentiated amoxicillin (Augmentin; GlaxoSmithKline) intravenously, a transdermal 25 μg/hour fentanyl patch (Durogesic; Janssen-Cilag), 0.2 mg/kg butorphanol (Torbugesic; Fort Dodge) intramuscularly, and oxygen therapy.

After 24 hours, neurological examination revealed marked improvement in mental status (Garosi 2004). At this time paralysis of the distal right forelimb caudal to the elbow and absent deep pain sensation on the lateral and dorsal aspects of the limb caudal to the elbow was discovered. Trauma to the caudal brachial plexus (C7-T2) was suspected.

Three days after presentation, neurological examination revealed a normal mental status, ambulatory tetraparesis with ataxia, and the right forelimb signs described above. Nasal septum sensation was present bilaterally, menace responses were present bilaterally, though mildly decreased on the left, and pupillary light reflexes were normal bilaterally. A right-sided Horner's syndrome and a mild right-sided head tilt were apparent.

CT of the skull was performed using a single-slice spiral scanner (HiSpeed Lx/i; GE); 1.0 mm thick helical slices were acquired in the transverse plane with a pitch of 1.0. Precontrast and postcontrast CT revealed multiple fractures including bilateral mandibular fractures and fractures of the right zygomatic arch and bones in the caudal nasal cavity. Additionally, there was a fracture of the calvarial portion of the right temporal bone along the lateral to rostrolateral aspect of the calvarium. Immediately beneath this fracture, in the region of the temporal and piriform lobes of the brain, there was an elongated pocket of low-attenuating tissue, which extended directly through the fracture line and blended with similar tissue in the retro-orbital space of the right eye (Fig 1). This tissue had Hounsfield unit measurements ranging from approximately -30 to -100 using a region of interest within the tissue (Osirix v3.7).

FIG. 1

Transverse (a and b) and dorsal (c and d) CT images of a cat's skull in both bone (a and c) and soft tissue (b and d) windowing. The images show a fractured right temporal bone with low-attenuating tissue compressing the cerebrum, which is continuous with the retrobulbar fat. The tissue had Hounsfield unit measurements between -30 and -100, consistent with adipose tissue

Over the following week, a nasogastric tube was placed for feeding, the mandibular symphysis was reduced and stabilised with a cerclage wire, and the jaw was shut using a bi-gnathic encircling and retaining device (Nicholson and others 2010). At this time the results from a neurological examination was normal apart from monoplegia and anaesthesia of the right forelimb, as previously discussed, and right-sided Horner's syndrome.

Based on initial evaluation of the CT, the differential diagnoses for the low-attenuating tissue in the brain case were air and fat. Hounsfield units give indirect evidence about the nature of the tissue being evaluated, and the measurements here were within the published range for fat (Hounsfield 1980, Sjöström and others 1986, Tokiguchi and others 1986). The source was retrobulbar fat entering the cranium through a fracture in the right temporal bone.

In the veterinary literature, pneumocephalus has been reported secondary to trauma and craniotomy (Garosi and others 2002, Fletcher and others 2006, Cavanaugh and others 2008, Thieman and others 2008, Haley and Abramson 2009). In these cases, the animals had clinical signs secondary to pneumocephalus that resolved once the underlying problem was surgically corrected. In the case reported here, the animal's mentation change was most likely due to concussive head trauma rather than compression of the cerebrum by fat. Successful treatment was accomplished with standard conservative management of head trauma without the need for surgical intervention.

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