Contributors: Fraser McConnell

 Species: Feline   |   Classification: Miscellaneous

Introduction

Overview

Radiographic considerations

  • Fine detail screens are preferred.
  • A low kV high mAs maximizes contrast.
  • Non-screen film (eg dental film) or a small flexible cassette and single screen is ideal for nasal chambers.
  • At least 2 projections are mandatory. Opposing oblique views are often helpful.
  • The area of the skull radiographed should be tailored to the clinical signs.

Nasal chambers and paranasal sinuses

  • DV intra-oral (occlusal) projection is generally most useful for the nasal chambers and rostral teeth.
  • VD open mouth less useful than intra-oral for rostral region but better for frontal sinuses.
  • Lateral projection allows evaluation of sinuses and nasal and frontal bones.
  • The lateral projection is often normal or shows only subtle changes despite gross changes on DV projection by superimposing normal structures over abnormal regions in the presence of unilateral disease.
  • Rostrocaudal oblique projection of frontal sinuses is best choice to evaluate frontal sinus involvement but is difficult to obtain in many cats.
  • DV or VD skull occasionally helpful if disease extends into orbits.

Aural

  • DV, lateral-oblique and open-mouth rostrocaudal obliques are most useful for evaluation of the bullae.
  • It is helpful to take both lateral obliques to compare sides or rostrocaudal open mouth oblique.
Orbital and retrobulbar
  • DV or VD is the most useful projection.
  • Use of lateral projection is limited.
  • DV intra-oral may be of value in evaluating the medial wall of the orbit if the non-screen film can be placed caudal to molar teeth.
  • Opposing oblique views and/or rostrocaudal view of the orbits may provide additional bony detail.

    Nasolacrimal system requires contrast studies for evaluation.

    Temporomandibular joint

  • Lateral oblique of each joint and DV projections most useful.
  • It may be helpful to take open and closed mouth radiographs to identify subluxation of the TMJ.
  • Taking radiographs of both sides aids interpretation.

    Cranial vault

  • Lateral, DV, lesion-orientated oblique and rostrocaudal oblique projections are most useful.

    Radiographs often significantly underestimate the size of skull masses and give no information about extent of any brain invasion.

    Restraint

  • Radiography of the skull requires general anesthesia. This is the only way to obtain accurate projections.
  • The endotracheal tube may need to be removed for certain projections to avoid superimposition of the areas of interest. Tying the tube to the mandible instead of maxilla may reduce superimposition for nasal and sinus evaluations.

Indications

Nasal chambers and paranasal sinuses

Orbital and retrobulbar

  • Exophthalmos.
  • Pain on opening mouth.

Aural

Cranial vault

  • Palpable swellings.
  • Following trauma - although neurological status is more important than radiographic change.

Radiographic anatomy

  • There is relatively little variation in skull shape.
  • Brachycephalic breeds have smaller sinuses and shorter noses.
  • Male cats have larger sinuses than female cats. 
  • The nasal chambers are contained within a bony case   Skull: normal lateral radiograph  comprising:
    • Maxillary bone laterally.
    • Palatine, vomer and incisive bones ventrally.
    • Nasal bone dorsally.
  • The cartilagenous septum divides the nasal chamber into left and right chambers and is usually straight   Skull: normal nasal chambers - intra-oral radiograph  but in some normal cats the vomer/septum is bowed.

The septum seen on radiographs is the combined shadow of vomer bone and septum.

  • Nasal dorsal and ventral conchae are superimposed and appear as fine linear mineralized lines extending from incisive bone caudally to PM 3 or 4.
  • The ethmoid turbinates are thicker and more widely spaced and lie caudal to the nasal conchae and will slightly criss-cross one another.
  • Frontal sinuses are best seen in lateral oblique view   Skull: frontal sinus normal - radiograph lateral  or rostrocaudal oblique (although not possible to obtain in many cats).

Aural

  • Horizontal ear canal should have gas opacity and parallel sides.
  • On DV extends laterally from tympanic bullae.
  • Auricular cartilage has soft tissue opacity.
  • Tympanic bullae should be symmetrical with thin, uniform thickness walls and gas filled lumen   Skull: normal tympanic bullae - rostro caudal open mouth view  .

Orbit and retrobulbar

  • The walls of the orbit are formed by:
    • The zygomatic arch laterally.
    • The pterygoid muscle ventrally.
    • Lacrimal and frontal bones medially.
    • Orbital ligament - not normally visualized unless partly mineralized (incidental finding in many cases).

Temporomandibular joint

  • Condylar joint with transversely elongated mandibular condyle articulating with mandibular fossa of temporal bone.
  • Joint surfaces should be smooth and slightly widened ventrally.

Cranial vault

  • The brain case comprizes 14 flat bones - 8 paired and 6 unpaired   Skull: normal lateral radiograph  .
  • Suture lines are clearly visible between the flat bones and should not be mistaken for fractures.
  • The intracranial surfaces of the bones have a dimpled 'copper-beaten'appearance.

Interpretation

Appearance

Nasal chambers

  • The nasal chamber should be carefully evaluated for turbinate destruction, alterations of opacity and deviation and lysis of vomer, septa and bony case.
  • Loss of visualization of nasal conchae with increased opacity may be due to effacement with soft tissue/fluid or destruction by mass.
  • Loss of visualization of ethmoturbinates only occurs with turbinate destruction and not effacement.

Normal radiographs may be seen with acute rhinitis, FB, viral, bacterial and allergic rhinitis.

  • Differentiation between rhinitis and neoplasia is often extremely difficult in cats (cf dog).

Chronic hyperplastic rhinitis

  • Usually bilateral.
  • Diffuse, ill-defined increase in opacity with blurring of turbinates and conchae   Turbinate: rhinitis - intra-oral radiograph  .
  • No distortion or lysis of bony case or vomer/septum.
  • In severe cases may be focal destruction of turbinates but mild and without soft tissue opacity superimposed.

Usually preferentially affects rostral aspect of nasal conchae.

Destructive rhinitis

  • Mixed pattern of patchy areas of density and predominantly reduced opacity due to turbinate destruction   Skull: rhinitis - intra-oral radiograph DV  .
  • Focal ill-defined areas of increased soft tissue/fluid density due to fungal granulomas.
  • May see focal punctate lysis of adjacent bone (not specific to aspergillosis) in frontal bone and adjacent sinus (with increase in frontal sinus opacity).
  • Does not cause septal deviation.

Foreign body

  • Usually non-radiopaque, eg grass awn. Occasionally displaced tooth with present as a nasal foreign body.
  • May see focal rhinitis characterized by focal soft tissue/fluid opacity with minimal turbinate destruction .
  • Septum and bony case will be unaffected.

Rhinitis

  • Acute viral rhinitis usually normal radiographs.
  • May see blurring of turbinates due to discharge.

Neoplasia

  • Cannot differentiate types radiographically.
  • Increased soft tissue opacity combined with destruction of ethmoturbinates and nasal conchae   Skull: nasal lymphoma - intra-oral radiograph  .
  • Usually unilateral initially but in later stages affect both sides. Lymphoma may be bilateral.
  • Often cause bowing and erosion of vomer/septum   Nasal cavity: anaplastic carcinoma - intra-oral radiograph  .
  • In later stages of disease may erode through the nasal and maxillary bone or cribriform plate into brain or orbit.
  • Distortion or lysis of vomer/septum is most specific finding for nasal tumor.
  • Often originate caudally in the nasal cavity.

Frontal sinus

  • Often affected by extension of nasal disease.
  • There may be opacification of frontal sinus due to tumor expansion or retention of secretions due to blockage of drainage .
  • Sinus may appear normal on lateral but DV or rostrocaudal oblique projection shows loss of gas opacity.

May be impossible to differentiate opacification due to mass and fluid trapping.

  • Chronic obstruction to drainage can result in frontal mucocele(enlargement of sinus) - the surrounding bone usually appears normal.

Fractures

  • Often depressed and may need oblique projections to highlight fracture lines.

Should all be considered open fractures due to communication with sinus cavity.

Lysis of frontal bone

  • Neoplasia:
    • Often very aggressive with severe bone lysis.
    • May arise within sinus or extend from adjacent tissue.

Aural

Horizontal canal

  • Loss of air opacity in the horizontal canal may be due to accumulation of secretions, luminal masses, eg polyps, tumor, avulsion of cartilage or congenital aplasia.
  • Mineralization of aural cartilages (and narrowing of the canal) is seen with chronic inflammation.
  • Narrowing of lumen occurs with chronic inflammation and hyperplastic mucosa, or less commonly, compression by extraluminal masses.

Tympanic bullae

  • Many diseases cause similar radiographic signs.
  • Increased opacity- due to fluid accumulation, polyps   Skull: tympanic bulla disease - radiograph DV  .

Soft tissue, eg tongue superimposed over bullae on oblique view can mimic lack of aeration.

  • Lysis- neoplasia or osteomyelitis.
  • Thickening of wall with infection, inflammation with nasopharyngeal polyps.

Wispy mineralization of soft tissue and lysis without evidence of sclerosis is highly suggestive of neoplasia.

  • Enlarged bullae- usually slow-growing luminal mass, eg polyp.

Loss of continuity of bulla wall and opacification of bulla may be seen following bulla osteotomy. The bulla wall may reform after surgery but with distortion and thickening.

Otitis media

  • Thickening of bulla wall without lysis, or opacification of bullae   Skull: otitis media - radiograph DV  .
  • May see concurrent stenosis of horizontal ear canal.

Orbit

  • Many causes of retrobulbar disease do not produce radiographic changes.

Ultrasonography is often more useful for evaluation.

Neoplasia

  • Arising from within the orbit, eg lymphoma   Lymphoma  often produce no radiographic changes.
  • Tumors arising from the nasal cavity and extending into the orbit show typical signs of nasal changes and lysis of the frontal bone.

Foreign bodies

  • May be visualized if opaque, eg bullets.
  • It is often difficult to assess radiographically the position of the FB relative to the globe.

Ultrasonography is preferred for this.

Retrobulbar cellulitis

  • Often normal radiographically but may see changes if associated with periapical abscess.
  • If detect disease may see loss of lamina dura, focal lysis surrounding tooth root with adjacent sclerosis.
  • Widening of pulp cavity in some cases.

Temporomandibular joint

  • Joint should be evaluated as for appendicular skeletal joints.
  • Conditions affecting joint are the same as other synovial joints.

Osteoarthritis

  • Osteophyte formation on retroarticular process.
  • May see irregularities of joint surfaces in severe cases.
  • Shallow mandibular fossa and flattening of condyles seen with dysplastic joints .

Destruction

  • Seen with osteomyelitis and neoplasia.
  • Extension of disease from adjacent structures especially middle ear.

Fractures

  • Often concurrent luxation of TMJ .

Craniomandibular osteopathy

  • New bone formation may involve TMJ resulting in inability to open jaw.

Cranial vault

Fractures

  • Need to be differentiated form normal symmetrical suture lines.

Fractures often only visible when radiographed tangentially therefore multiple projections may be required.

  • There is usually soft tissue swelling over the fracture and gas may be visible within soft tissue, eg after dog bite.

Hydrocephalus

  • Acquired disease is normal radiographically.
  • Congenital disease may   →   enlargement of brain case with loss of normal copper -beaten appearance. Fontanelles may be wide.
  • MRI   Magnetic resonance imaging: brain  is the best method for evaluating intracranial disease.

Neoplasia

  • Variable appearance depending on type:
    • Osteoma- benign tumor with no lysis and dense homogeneous periosteal new bone with smooth margins.
    • Chondrosarcoma  Chondrosarcoma   orosteosarcoma  Osteosarcoma  - variable lysis and perisoteal new bone. Tend be more clearly defined than appendicular bone tumors with organized new bone formation.
    • Meningiomas - may cause local hyperostosis (bone thickening) of the overlying skull and occasionally the tumor mineralizes.

Often have granular mineralization.