What Is Your Diagnosis?

Danielle M. Zwueste Department of Small Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK S7N 5B4, Canada.

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Lesley A. Zwicker Spinnaker Veterinary Imaging Inc, Bridgewater, Nova Scotia, B4V 3X9, Canada

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History

A 4-month-old sexually intact female domestic shorthair kitten had a history of apparent visual deficits, abnormal behavior, and seizures and appeared slow to learn since being rescued and fostered at approximately 1 month of age. Information regarding littermates was not available. Vaccinations were up to date, and there had been no travel history since adoption. Findings on ophthalmologic examination were unremarkable.

The kitten was referred to the Western College of Veterinary Medicine for further evaluation. Findings on physical examination were unremarkable. Neurologic examination revealed mild obtundation, failure to visually track cotton balls, an absent menace response bilaterally, and postural reaction deficits in all 4 limbs. These signs were consistent with diffuse cerebral disease. No abnormalities were detected on CBC, serum biochemistry analysis, and preprandial and postprandial measurements of serum bile acids concentration. The kitten had negative serologic ELISA results for FeLV and FIV infections. No abnormalities were detected on thoracic radiography. The kitten was placed under general anesthesia, and MRI of the brain was performed (Figure 1).

Figure 1—
Figure 1—

T2-weighted parasagittal (A) and transverse (B and C) MRI images of the brain of a 4-month-old sexually intact female domestic shorthair kitten that was referred because of a history of apparent visual deficits, abnormal behavior, seizures, and apparent learning deficits since being rescued and fostered at approximately 1 month of age. B—Image was obtained at the level of the midbrain. C—Image was obtained at the level of the caudal aspect of the occipital lobe.

Citation: Journal of the American Veterinary Medical Association 252, 10; 10.2460/javma.252.10.1207

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page

Diagnostic Imaging Findings and Interpretation

On T2-weighted images, the lateral ventricles are enlarged, with the right more severely affected (Figure 2). The right lateral ventricle has an irregular shape and is continuous with a cavity extending caudally to the subarachnoid space and occipital bone, where the right occipital lobe has a markedly reduced volume. The right hippocampal body cannot be identified on transverse imaging. The left lateral ventricle also communicates with a cavity within the occipital lobe ventrally, although this is associated with a smaller cerebral defect. The cavities are isointense to the ventricular CSF.

Figure 2—
Figure 2—

Same images as in Figure 1. A—Notice the cavity extending from the right lateral ventricle to the caudodorsal aspect of the occipital lobe (asterisk). The cavitation appears to extend to the subarachnoid space and is isointense to the ventricular CSF on T2-weighted images. B—Notice the bilateral ventriculomegaly and reduced occipital lobe volume, with the right being more severely affected. The left hippocampus is readily visualized (arrow) but the corresponding contralateral structure is absent. C—Further caudally, the cavitation is also seen to extend to the ventrolateral aspect of the right occipital lobe (asterisk). The left ventrolateral occipital lobe is similarly affected but less severely (arrow).

Citation: Journal of the American Veterinary Medical Association 252, 10; 10.2460/javma.252.10.1207

On fluid attenuation inversion recovery (FLAIR) MRI imaging, the signal from within the ventricles and cavities was completely suppressed (Figure 3). T1-weighted images obtained following IV administration of gadobutrola (0.2 mmol/kg [0.09 mmol/lb]) did not reveal contrast enhancement. A diagnosis of hydrocephalus ex vacuo and bilateral porencephaly was made and was considered to be congenital in origin.

Figure 3—
Figure 3—

Transverse T2-weighted fluid attenuation inversion recovery images of the kitten in Figure 1. Images were obtained at the same level of the midbrain (A) and the caudal aspect of the occipital lobe (B) as depicted in Figure 1. A—The signal from within the lateral ventricles is completely suppressed bilaterally. B—The signal from within the right (asterisk) and left (arrow) occipital lobe cavities is similarly suppressed, suggesting the cavities are filled with CSF and contiguous with the ventricles.

Citation: Journal of the American Veterinary Medical Association 252, 10; 10.2460/javma.252.10.1207

Treatment and Outcome

Cerebrospinal fluid was collected via cerebellomedullary cisternal puncture, and findings on both gross examination and cytologic evaluation of the CSF sample were unremarkable. Treatment with phenobarbitalb (1 mg/kg [0.45 mg/lb], PO, q 12 h) was initiated, and the patient was discharged from the hospital. The kitten was euthanized 4 weeks later because of persistent seizures. A necropsy was performed. On histologic evaluation of brain specimens, dilated lateral and third ventricles lined by flattened, cuboidal ependymal cells were observed. The subcortical white matter was thinned with degeneration, edema, vacuolated myelin, and axonal swellings.

Comments

Several cavitary lesions have been identified in veterinary medicine, the definitions of the variations can be confusing, and consensus within the literature is often lacking. Porencephaly is most consistently described as a focal congenital cystic or cavitary lesion within a cerebral hemisphere, which often communicates with the subarachnoid space or the lateral ventricles.1,2 Porencephaly is infrequently reported for cats, and bilateral lesions even less so. The cavities result from fetal and perinatal brain destruction secondary to several possible insults such as ischemia and toxins, with feline panleukopenia virus being of particular importance.2,3 As in the case described in the present report, contrast enhancement of the cavitations is rarely reported.2 Hydranencephaly is another form of congenital cerebral cavitation, but is the result of a more global tissue loss and results in almost complete absence of the hemisphere.1 In cases of hydranencephaly, the meninges as well as the lateral ventricles remain intact but the cortical tissue is replaced by fluid-filled sacs.4 Although suspicion of porencephaly can be raised when cerebral signs such as seizures, aberrant behavior, and vision deficits are noted in pediatric animals, MRI is essential to confirm the diagnosis and rule out other congenital malformations or acquired processes such as infectious diseases.

Hydrocephalus is defined as the enlargement of all or part of the ventricular system and can be described as communicating, obstructive, or ex vacuo.4 Communicating hydrocephalus is characterized by bilateral, symmetric ventricular dilation without any detectable lesion. Obstructive hydrocephalus is secondary to either partial or complete restriction of CSF flow and may be associated with signs of increased intracranial pressure such as flattening of the sulci or brain herniation (transtentorial or transforaminal).5 Hydrocephalus ex vacuo is compensatory and CSF passively occupies a void left by primary tissue loss.4 Magnetic resonance imaging was pivotal in differentiating the hydrocephalus of the case described in the present study as ex vacuo, as there was no evidence of obstruction identified and there was apparent loss of parenchymal tissue leading to ventricular expansion.

Hippocampal asymmetry was a feature of the case described in the present report, which has been previously associated with porencephaly.2,3 The exact relationship between porencephaly and hippocampal atrophy is unknown, but 1 proposed mechanism is ischemic insult to the middle cerebral artery and its branch, the rostral choroidal artery.3 The hippocampal asymmetry may have been a contributing factor to the intractable epilepsy that ultimately led to euthanasia of the kitten, although the porencephaly itself may have generated a seizure focus; ratios of hippocampal asymmetry and porencephaly cysts have both been associated with seizure severity.3 Hippocampal volumetry has been used to identify hippocampal atrophy and hippocampal sclerosis.6 In 1 study,7 epileptic dogs had larger hippocampal asymmetry ratios than control dogs but there was no correlation noted between the ratio and seizure type, seizure severity, or the affected period. Hippocampal necrosis with secondary prolonged and repeated seizure events cannot be excluded for the kitten of the present report.

Ventriculomegaly and interhemispheric cysts have recently been reported for cats as an inherited neurologic syndrome.8 There were shared imaging properties with the case described in the present report, such as communication with the ventricular system and a supratentorial location. The interhemispheric cysts, however, are typically located at midline and associated with several other midline structure defects such as malformation of the corpus callosum, interthalamic adhesion, and septum pellucidum. These concurrent anomalies were not identified on the MRI images of the present report, and the presence of these structures was subsequently confirmed by histologic examination.

Feline infectious peritonitis is an important differential diagnosis for ventriculomegaly and hydrocephalus in young cats. Immune-mediated reaction to virally infected macrophages leads to granulomatous meningitis, ependymitis, and vasculitis.9 Although antemortem diagnosis can be difficult, MRI is a useful tool and can identify ventricular dilation and hydrocephalus, intraventricular hyperintensity on FLAIR imaging caused by proteinaceous and cellular CSF, and periventricular contrast enhancement. The contrast enhancement can affect 1 or more ventricles and correlates with pathological lesions.9 The case described in the present report did not have any of the expected contrast enhancement, and the signal within the ventricles and cavities was fully suppressed on FLAIR sequences. Hydrocephalus caused by feline infectious peritonitis is considered obstructive as CSF flow is partially or completely impaired because of increased viscosity of the CSF and occlusion of the ventricular system.9 The hydrocephalus in the kitten in the present report was considered to be ex vacuo, which further rules out feline infectious peritonitis as a cause for the imaging findings.

Footnotes

a.

Gadavist (1.0 mmol/mL), Bayer, Mississauga, ON, Canada.

b.

Phenobarbital (120 mg/mL), Sandoz, Boucherville, QC, Canada.

References

  • 1. Davies ESS, Vollk HA, Behr S, et al. Porencephaly and hydranencephaly in six dogs. Vet Rec 2012;170:179184.

  • 2. Schmidt MJ, Klumpp S, Amort K, et al. Porencephaly in dogs and cats: magnetic resonance imaging findings and clinical signs. Vet Radiol Ultrasound 2012;53:142149.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3. Hori A, Hanazono K, Miyoshi K, et al. Porencephaly in dogs and cats: relationships between magnetic resonance imaging (MRI) features and hippocampal atrophy. J Vet Med Sci 2015;77:889892.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Vandevelde M, Higgins RJ, Oevermann A. Veterinary neuropathology. Chichester, England: John Wiley & Sons Ltd, 2012.

  • 5. Bittermann S, Lang J, Henke D, et al. Magnetic resonance imaging signs of presumed elevated intracranial pressure in dogs. Vet J 2014;201:101108.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6. Geuze E, Vermetten E, Bremner JD. MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders. Mol Psychiatry 2005;10:160184.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Kuwabara T, Hasegawa D, Kobayashi M, et al. Clinical magnetic resonance volumetry of the hippocampus in 58 epileptic dogs. Vet Radiol Ultrasound 2010;51:485490.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8. Keating MK, Sturges BK, Sisó S, et al. Characterization of an inherited neurological syndrome in Toyger cats with forebrain commissural malformations, ventriculomegaly and interhemispheric cysts. J Vet Intern Med 2016;30:617626.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9. Foley JE, Lapointe JM, Poland A, et al. Diagnostic features of clinical neurological feline infectious peritonitis. J Vet Intern Med 1998;12:415423.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Figure 1—

    T2-weighted parasagittal (A) and transverse (B and C) MRI images of the brain of a 4-month-old sexually intact female domestic shorthair kitten that was referred because of a history of apparent visual deficits, abnormal behavior, seizures, and apparent learning deficits since being rescued and fostered at approximately 1 month of age. B—Image was obtained at the level of the midbrain. C—Image was obtained at the level of the caudal aspect of the occipital lobe.

  • Figure 2—

    Same images as in Figure 1. A—Notice the cavity extending from the right lateral ventricle to the caudodorsal aspect of the occipital lobe (asterisk). The cavitation appears to extend to the subarachnoid space and is isointense to the ventricular CSF on T2-weighted images. B—Notice the bilateral ventriculomegaly and reduced occipital lobe volume, with the right being more severely affected. The left hippocampus is readily visualized (arrow) but the corresponding contralateral structure is absent. C—Further caudally, the cavitation is also seen to extend to the ventrolateral aspect of the right occipital lobe (asterisk). The left ventrolateral occipital lobe is similarly affected but less severely (arrow).

  • Figure 3—

    Transverse T2-weighted fluid attenuation inversion recovery images of the kitten in Figure 1. Images were obtained at the same level of the midbrain (A) and the caudal aspect of the occipital lobe (B) as depicted in Figure 1. A—The signal from within the lateral ventricles is completely suppressed bilaterally. B—The signal from within the right (asterisk) and left (arrow) occipital lobe cavities is similarly suppressed, suggesting the cavities are filled with CSF and contiguous with the ventricles.

  • 1. Davies ESS, Vollk HA, Behr S, et al. Porencephaly and hydranencephaly in six dogs. Vet Rec 2012;170:179184.

  • 2. Schmidt MJ, Klumpp S, Amort K, et al. Porencephaly in dogs and cats: magnetic resonance imaging findings and clinical signs. Vet Radiol Ultrasound 2012;53:142149.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 3. Hori A, Hanazono K, Miyoshi K, et al. Porencephaly in dogs and cats: relationships between magnetic resonance imaging (MRI) features and hippocampal atrophy. J Vet Med Sci 2015;77:889892.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 4. Vandevelde M, Higgins RJ, Oevermann A. Veterinary neuropathology. Chichester, England: John Wiley & Sons Ltd, 2012.

  • 5. Bittermann S, Lang J, Henke D, et al. Magnetic resonance imaging signs of presumed elevated intracranial pressure in dogs. Vet J 2014;201:101108.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 6. Geuze E, Vermetten E, Bremner JD. MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders. Mol Psychiatry 2005;10:160184.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Kuwabara T, Hasegawa D, Kobayashi M, et al. Clinical magnetic resonance volumetry of the hippocampus in 58 epileptic dogs. Vet Radiol Ultrasound 2010;51:485490.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 8. Keating MK, Sturges BK, Sisó S, et al. Characterization of an inherited neurological syndrome in Toyger cats with forebrain commissural malformations, ventriculomegaly and interhemispheric cysts. J Vet Intern Med 2016;30:617626.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 9. Foley JE, Lapointe JM, Poland A, et al. Diagnostic features of clinical neurological feline infectious peritonitis. J Vet Intern Med 1998;12:415423.

    • Crossref
    • Search Google Scholar
    • Export Citation

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