Canis ISSN: 2398-2942

Computed tomography: brain

Synonym(s): CT brain

Contributor(s): Federica Morandi, Tobias Schwartz

Introduction

  • In recent years computed tomography (CT) Computed tomography has become more readily available in the veterinary field.
  • CT uses x-ray to generate cross-sectional images of the body that avoid the superimposition of neighboring structures, which makes it particularly useful when imaging areas of complex anatomy, such as the skull. Furthermore, CT provides excellent contrast resolution, many times superior to that of conventional radiography, and is recognized as superior to all other imaging modalities for imaging bone. In general, however, MRI Magnetic resonance imaging: brain is preferred over CT for brain imaging due to its superior soft tissue contrast.
  • CT has been traditionally carried out with the patient under general anesthesia, since the animal must remain immobile for the duration of the scan, usually 3-10 minutes depending on the area imaged. With the implementation of helical CT in the 80's, and more so with the newly developed multiple row detectors CT scanners in the late 90's, the time necessary for image acquisition has dramatically decreased. A state-of the-art multislice scanner can acquire images of the whole body of an adult man in <12 seconds, of the entire thorax in approximately 3 seconds. Even if the cost of such equipment makes it prohibitive in a veterinary practice, single slice helical scanners allow for shorter acquisition times for which patient immobilization may be achieved using heavy sedation alone, rather than general anesthesia. This has the potential to increase the number of animals that can be scanned as well as allowing scanning of animals that are not good candidates for anesthesia.

Uses

Indications

Advantages

  • The major advantage of CT over conventional radiographs is the higher contrast resolution: CT can discriminate density differences in tissues of 0.25-0.5%, whereas radiography can only differentiate differences of about 10%.
  • Cross-sectional images avoid superimposition of structures in areas of complex anatomy, which is a great advantage for the skull and nose.
  • Pre and postprocessing manipulation of the raw CT data is possible, allowing tissues of varying density to be better evaluated.
  • Multiplanar image reconstruction and 3D renderings can be configured.
  • Initial cost and maintenance of equipment is often less than MRI Magnetic resonance imaging: basic principles Magnetic resonance imaging: brain.
  • Imaging times are significantly reduced as compared to MRI, even when axial (conventional) CT is used, and more so with single slice helical (and multiple-row detectors) scanners.
  • Refurbished CT equipment can be purchased at affordable prices.
  • CT is superior to all other imaging modalities when examining bone.
  • Patients with metallic implants/foreign material in the head can usually still be imaged (this is generally not possible with MRI).
  • With single-slice helical, and more so with the newest multiple-row detectors scanners, sedation alone could be sufficient for restraint.

Disadvantages

  • General anesthesia is typically required for older, single-slice scanners General anesthesia: overview.
  • Area of interest must fit within the CT gantry (usually not a problem when imaging the canine head).
  • Standard CT tables are designed to accommodate the human torso and have weight limitations of 150-200 kg (usually not a problem when imaging dogs).
  • Study interpretation may be lengthy due to the large number of images acquired with most CT examinations.
  • Ionizing radiation is utilized.
  • Low sensitivity for vascular and inflammatory lesions compared to MRI.
    For most intracranial disease MRI is more informative due to better soft tissue contrast.
  • High density streak artifacts from metal implants/foreign material may reduce image quality.
  • Caudal fossa imaging (cerebellum and brainstem) can be problematic due to beam hardening artifact.

Requirements

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Preparation

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Procedure

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Aftercare

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Outcomes

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Prognosis

Image interpretation

  • Normal anatomy:
    • Structures that normally show contrast enhancement include the pituitary gland, choroid plexus and falx cerebri.
    • The shape of the brain vary slightly between breeds of dogs, depending on the head conformation.
    • In brachycephalic dogs the frontal sinus is very small or absent.
    • There is a great degree of variation in the size of the lateral ventricles, especially in dome-headed dogs (Bulldogs Bulldog , Chihuahua Chihuahua - Smooth Coat , Yorkshire terriers Yorkshire Terrier , Pugs Pug ).
    • In animals with congenital hydrocephalus, there is often incomplete closure of the fontanelle and other suture lines.
    • The lateral ventricles can also be asymmetrical; in the absence of a mass effect and/or deviation of the septum, this is most likely a variation of normal.
  • Pathology:
    • Tumors:
      • Meningiomas Meningioma Brain: transverse - pre-IV contrast CT Brain: transverse - post-IV contrast CT :
        • Extra-axial (outside the brain).
        • Usually iso- to slightly hyper-attenuating on pre-contrast images.
        • May show mineralizations.
        • Cystic meningiomas have been reported.
        • May be associated with hyperostosis of the overlying calvarium.
        • Mass effect is variable depending on the size.
        • May be multiple (especially in cats).
        • After IV contrast administration show uniform, intense enhancement, due to the abundant vascularity and location outside the blood-brain barrier.
        • A dural tail sign is difficult to see compared to MRI images.
    • Pituitary tumors Pituitary adenoma Brain: pituitary - transverse pre-IV contrast CT Brain: pituitary - transverse post-IV contrast CT Brain: pituitary mass - transverse post-IV contrast CT Brain: pituitary mass - dorsal post-IV contrast CT :
      • Extra-axial (outside the brain).
      • Usually iso- to mildly hyper-attenuating on pre-contrast images.
      • Well defined mass located dorsal to the sella pituitaria.
      • After IV contrast administration show uniform, intense enhancement, similar to meningiomas.
    • Choroid plexus tumors:
      • Extra-axial, well defined mass associated with the ventricles.
      • Often associated with hydrocephalus due to CSF production by the tumor.
      • After IV contrast administration show uniform, intense enhancement, similar to meningiomas.
    • Gliomas:
      • Intra-axial (inside the brain).
      • Often cause marked mass effect depending on location, size and presence of associated peritumoral edema.
      • The tumor itself is virtually never seen on pre-contrast images.
      • Contrast enhancement is very variable but usually not very intense: it can range from no discernible enhancement, to ring (peripheral) enhancement to mild and patchy enhancement.
      • There can be significant peritumoral edema, seen as surrounding patchy areas of hypoattenuation.
      • In general MRI is more sensitive than CT in detecting gliomas.
    • Metastasis Brain: metastases 01 - transverse post-contrast CT Brain: metastases 02 - transverse post-contrast CT :
      • Rare in the dog.
      • Should be considered when more than one lesion is seen.
      • Enhancement is variable; in humans, there can be significant associated peritumoral edema.
    • Other Brain: trigeminal nerve 01 - transverse post-contrast CT Brain: trigeminal nerve 02 - transverse post-contrast CT :
      • Trigeminal nerve neoplasia:
        • Contrast enhancing mass just dorsal to the oval foramen.
    • Inflammatory lesions Brain: GME - transverse pre-IV contrast CT Brain: GME - transverse post-IV contrast CT Brain: GME - transverse dorsal post-IV contrast CT :
      • Multifocal lesions of variable size, often ill-defined.
      • Patchy enhancement of the brain parenchyma.
      • Meningitis Meningitis alone is difficult to diagnose due compared to MRI.
      • Brain abscesses are rare in the dog; they appear as hypoattenuating masses with thick, enhancing wall.
      • In some cases the brain can appear completely normal.
      • Cause: GME Granulomatous meningoencephalomyelitis , fungal (variable geographical distribution), bacterial, viral, parasitic.
    • Trauma CT: Skull: fracture (01) transverse - soft tissue window CT: Skull: fracture (02) transverse - soft tissue window :
      • Ideally performed with sedation alone if single slice helical (or multislice helical scanner) is available.
      • May be performed without any sedation in the comatose patient as long as the animal is immobile (for instance, strapped to a board).
      • Skull fractures, brain edema, intracranial hematomas and parenchymal hemorrhages can be identified:
        • CT is very sensitive for the detection of intracranial and parenchymal hemorrhage and hematomas in the acute phase.
        • CT is very sensitive in detecting intracranial gas.
    • Congenital lesions:
      • Hydrocephalus Hydrocephalus CT: Brain: hydrocephalus transverse - soft tissue window :
        • Identifying the lateral ventricles is easy; more challenging is to determine how much dilation is too much (especially in the absence of any other abnormalities), given the great variation in size observed among various breeds
    • Chiari malformation Neurology: Chiari-like malformation/syringomyelia (CM/SM) in Cavalier King Charles spaniels (crowding of the foramen magnum with cerebellar herniation, hydrocephalus and syringomyelia):
      • Sagittal reconstructions needed.
      • MRI is superior for the diagnosis of this pathology.
    • Vascular lesions:
      • MRI is superior for the diagnosis of brain infarcts.
    • Metabolic diseases:
      • CT of limited value, MRI is superior for the diagnosis of metabolic disease.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • De Rycke L M, Gielen I M, Van Meervenne S A et al (2005) Computed tomography and cross-sectional anatomy of the brain in clinically normal dogs. Am J Vet Res 66 (10), 1743-1756 PubMed.
  • Polizopulou Z S, Koutinas A F, Souftas V D et al (2004) Diagnostic correlation of CT-MRI and histopathology in 10 dogs with brain neoplasm. J Vet Med A Physiol Pathol Clin Med 51 (5), 226-231 PubMed.
  • Porat-Mosenco Y, Schwarz T, Kass P H (2004) Thick section reformatting of thinly collimated computed tomography for reduction of skull-base-related artifacts in dogs and horse. Veterinary Radiology and Ultrasound 45 (2), 131-135 PubMed.
  • van der Vlugt-Meijer R H, Meji B P, Voorhout G (2004) Dynamic computed tomographic evaluation of the pituitary gland in healthy dogs. Am J Vet Res 65 (11), 1518-1524 PubMed.
  • Gandini G, Gentilini F, Cimatti L et al (2003) Evaluation of the clinical signs and computed tomographic findings in 27 dogs with intracranial space-occupying lesions (1999-2000). Veterinary Research Communications 27 (Suppl 1), 399-401 PubMed.
  • Kube S A, Bruyette D S, Hanson S M (2003) Astrocytomas in young dogs. JAAHA 39 (3), 288-293 PubMed.
  • Nykamp S G, Steffey M A, Scrivani P V et al (2003) Computed tomographic appearance of epidural empyema in a dog. Canadian Veterinary Journal 44 (9), 729-731 PubMed.
  • Giroux A, Jones J C, Bøhn J H et al (2002) A new device for stereotactic CT-guided biopsy of the canine brain: design, construction, and needle placement accuracyVeterinary Radiology and Ultrasound 43 (3), 229-236 PubMed.
  • Moissonnier P, Blot S, Devauchelle P et al (2002) Stereotactic CT-guided brain biopsy in the dog. JSAP 43 (3), 115-123 PubMed.
  • Nykamp S G, Scrivani P V, de Lahunta A et al (2002) Chronic subdural hematoma and hydrocephalus in a dog. Veterinary Radiology and Ultrasound 42 (6), 511-514 VetMedResource.
  • van der Vlught-Meijer R H, Voorhout G, Meij B P (2002) Imaging of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism. Molecular and Cellular Endocrinology 197 (1-2), 81-87 PubMed.
  • Bergman R, Jones J, Lanz O et al (2000) Post-operative computed tomography in two dogs with cerebral meningioma. Veterinary Radiology and Ultrasound 41 (5), 425-432 PubMed.
  • Love N E, Fisher P, Hudson L (2000) The computed tomographic enhancement pattern of the normal canine pituitary gland. Veterinary Radiology and Ultrasound 41 (6), 507-510 PubMed.
  • Ducoté J M, Johnson K E, Dewey C W et al (1999) Computed tomography of necrotizing meningoencephalitis in 3 Yorkshire Terriers. Veterinary Radiology and Ultrasound 40 (6), 617-621 PubMed.
  • Cauzinille L (1997) Cerebrovascular accident in a two-year-old dog. A clinical case and review of non-traumatic vascular disorders of the brain in veterinary medicine. Pratique Medicale and Chirurgicale de l'Animal de Compagnie 32 (2), 143-150 VetMedResource.
  • Tidwell A S, Ross L A, Kleine L J (1997) Computed tomography and magnetic resonance imaging of cavernous sinus enlargement in a dog with unilateral exophthalmos. Veterinary Radiology and Ultrasound 38 (5), 363-370 PubMed.
  • Drost W T, Berry C R, Fisher P E (1996) Computed tomographic appearance of a normal variant of the canine tentorium cerebelli osseum. Veterinary Radiology and Ultrasound 37 (5), 351-353 VetMedResource.
  • Dzyban L A, Tidwell A S (1996) Imaging diagnosis: granulomatous meningoencephalitis in a dog. Veterinary Radiology and Ultrasound 37 (6), 428-430 VetMedResource.
  • Wolf M, Pedroia V, Higgins R J et al (1995) Intracranial ring-enhancing lesions in dogs: a correlative CT scanning and neuropathologic study. Veterinary Radiology and Ultrasound 36 (1), 16-20 VetMedResource.
  • Tidwell A S, Mahony O M, Moore R P et al (1994) Computed tomography on an acute hemorrhagic cerebral infarct in a dog. Veterinary Radiology and Ultrasound 35 (4), 290-296 VetMedResource.
  • Norton F (1992) Cerebral infarction in a dog. Progress in Veterinary Neurology (4), 120-125 VetMedResource.


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