Felis ISSN 2398-2950

Computed tomography: nasal chamber

Synonym(s): CT: nose

Contributor(s): Fraser J McConnell, Federica Morandi, Tobias Schwartz

Introduction

  • In recent years computed tomography (CT) Computed tomography (CT) 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 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, due to the requirement to 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 detector 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

  • Nasal discharge Nasal discharge.
  • Evaluation of suspected rhinitis Rhinitis and sinusitis (bacterial, fungal or due to foreign body).
  • Evaluation of suspected nasal neoplasia Nasal cavity: neoplasia and differentiation between nasal neoplasia and rhinitis. 
  • Pre-operative assessment prior to surgical excision of neoplastic processes.
  • Pre-operative assessment of complex fractures (multiplanar and 3D reformation).
  • CT-guided biopsy of a mass lesion.
  • Radiation therapy planning Radiotherapy.

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 density differencs 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 post-processing 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 usually cheaper 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 is often sufficient for restraint.

Disadvantages

  • General anesthesia is typically required General anesthesia: overview.
  • Study interpretation may be lengthy due to the large number of images acquired with most CT examinations.
  • Ionizing radiation is utilized.
    For extension of nasal disease into the brain MRI gives more information 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:
    • The shape and length of the nasal passages vary greatly between dolichocephalic and brachycephalic cats.
    • In brachycephalic cats the nose is very short and the frontal sinus is reduced in size.
    • Deviation of the nasal septum in the absence of a concurrent mass lesion usually represents a variation of normal and is commonly seen.
    • The pattern of the maxillary and ethmoid turbinates should be symmetrical.
    • The sphenoidal and frontal sinuses should be air filled.
  • Pathology:
    • Non-destructive (inflammatory) rhinitis Nasal passages 01: CT  Nasal passages 02: CT  Nasopharynx: CT 
      • Increased soft tissue density conforming to the turbinates (mucopurulent exudate, hemorrhage).
      • No evidence of a well-defined mass.
      • No evidence of bony lysis.
      • Uni or bilateral.
    • Destructive rhinitis:
      • Fungal (Cryptococcus Cryptococcosis) and severe viral rhinitis.
      • Most commonly generalized lesions.
      • Extensive lysis of the osseous turbinates with hyperlucency of the nasal passage(s):
        • Can be so severe to leave a completely "empty" nasal passage.
      • Lysis of the nasal septum/vomer bone.
      • Focal soft tissue masses representing fungal granulomata.
      • Mucosal thickening.
      • Soft tissue density in the frontal sinus may be due to fungal granulomas or exudate accumulation.
      • Thickening of the frontal bone indicates chronic osteomyelitis Osteomyelitis.
    • Chronic foreign body rhinitis Rhinitis:
      • Findings similar to fungal rhinitis.
      • The foreign body may only occasionally be visible as it may have dissolved over time.
    • Chronic lymphoplasmacytic rhinitis:
      • Bilateral > unilateral, often with one side more severely affected.
      • Lesions are most commonly diffuse or confined to the rostral aspect of the nose.
      • Increased soft tissue density (fluid accumulation, mucosal thickening).
      • Turbinate destruction usually mild.
      • Frontal sinus involvement if present usually mild.
    • Nasal neoplasia.
      • 40% are carcinomas (adenocarcinoma, squamous cell carcinoma), 30% lymphoma, 30% sarcomas (primarily osteosarcoma, fibrosarcoma, chondrosarcoma). 
      • Variable size mass associated with the nasal passage(s).
        • Mass can contain mineralizations, and can be primarily mineral in cases of primary bone tumors.
      • Extensive turbinate destruction.
      • Destruction of the nasal septum, maxilla, cribriform plate can be present depending on size, location and extent of the mass.
      • The mass can extend in the nasopharyngeal region, retro-orbital space, frontal sinus, external (facial) soft tissues and rostral aspect of the brain.
        • Can be difficult to differentiate mass from exudate:
          • If such differentiation is necessary, IV contrast can be used; otherwise, IV contrast is typically not necessary and does not aid in differentiating neoplastic from non-neoplastic lesions.
    • Congenital/traumatic lesions:
      • Given the ability to generate cross-sectional images and to create multiplanar and 3D reconstructions, CT can be very useful in evaluating complex fractures as well as congenital abnormalities.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Oliveira C R, O'Brien R T, Matheson J S et al (2012) Computed tomographic features of feline nasopharyngeal polyps. Vet Radiol Ultrasound 53 (4), 406-411 PubMed.
  • Karnik K, Reichle J K, Fischetti A J et al (2009) Computed tomographic findings of fungal rhinitis and sinusitis in cats. Vet Radiol Ultrasound 50 (1), 65-68 PubMed.
  • Reetz J A, Maï  W, Muravnick K B et al (2006) Computed tomographic evaluation of anatomic and pathologic variations in the feline nasal septum and paranasal sinuses. Vet Radiol Ultrasound 47 (4), 321-327 PubMed.
  • Tromblee T C, Jones J C, Etue A et al (2006) Association between clinical characteristics, computed tomography characteristics, and histologic diagnosis for cats with sinonasal disease. Vet Radiol Ultrasound 47 (3), 241-248 PubMed.


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