Contributors: Fraser McConnell

 Species: Canine   |   Classification: Miscellaneous

Introduction

Overview

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Radiographic considerations

  • Fine detail screens are preferred.
  • A low kV high mAs maximizes contrast.
  • Non-screen film or a small flexible cassette and screen is ideal for nasal chambers.
  • At least 2 projections are mandatory.
  • The different skull shapes are treated similarly for the basic projections.
    The small frontal sinus and domed head in many brachycephalic dogs Skull normal - radiograph lateral (Pug) 01 makes the skyline view of frontal sinus impossible.
  • Specialized projections such as tympanic bullae require adaptation of technique based on the shape of the skull.
  • The area of the skull radiographed should be tailored to the clinical signs.

Nasal chambers and paranasal sinuses

  • DV intra-oral (occlusal) Skull normal nasal chamber - radiograph intra-oral DV projection is generally most useful for the nasal chambers.
  • VD open mouth less useful than intra-oral.
  • Lateral projection Skull mesaticephalic 01 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.
  • Rostrocaudal oblique projection Skull frontal sinus normal - radiograph RCd of frontal sinuses is best choice to evaluate sinus involvement.
  • DV Skull normal - radiograph DV or VD skull occasionally helpful if disease extends into orbits.

Aural

  • DV Skull normal - radiograph DV , lateral Skull mesaticephalic 02 , lateral-oblique and open-mouth rostrocaudal Skull tympanic bulla normal - radiograph (open mouth) obliques are most useful.
  • It is helpful to take both lateral obliques to compare sides or rostrocaudal open mouth oblique.

Orbital and retrobulbar

  • DV Skull normal - radiograph 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 cassette and film can be placed caudal to molar teeth.
    Nasolacrimal system requires contrast studies for evaluation.

Temporomandibular joint

  • Lateral oblique Skull normal temporomandibular joint - radiograph oblique of each joint and DV Skull normal - radiograph 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 Skull mesaticephalic 01 , DV Skull normal - radiograph 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.

Indications
Nasal chambers and paranasal sinuses

Orbital and retrobulbar

  • Exophthalmos.
  • Pain on opening mouth.

Aural

Mandible and temporomandibular joint

  • Pain or difficulty opening the mouth.
  • Inability to close mouth (neurapraxia, open-mouth jaw locking).
  • Trauma with suspected fracture and symphyseal split.
  • Dental malocclusion.
  • Palpable swelling.
  • Lack of mandibular rigidity (rubber jaw).

Cranial vault

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

Radiographic anatomy

  • There are 3 basic skull types:
    • Brachycephalic Skull normal - radiograph DV (brachycephalic) - short, wide head.
    • Dolichocephalic Skull dolichocephalic - long, narrow head.
    • Mesaticephalic Skull mesaticephalic 01 - medium proportions.

Nasal chambers and sinuses

  • The nasal chambers are contained within a bony case 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 straight in most dogs Skull normal nasal chamber - radiograph intra-oral DV.
    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 oblique view or rostrocaudal Skull frontal sinus normal - radiograph RCd.

Aural

  • Horizontal ear canal should have gas opacity and parallel sides.
  • On DV extends laterally from tympanic bullae Skull normal - radiograph DV.
  • Auricular cartilage has soft tissue opacity.
  • Tympanic bullae should be symmetrical with thin, uniform thickness walls and gas filled lumen.
  • Breed variation in shape of bullae - brachycephalics (especially CKCS) have smaller, oval shaped bullae Skull normal brachycephalic - radiograph DV.

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 dogs).

Dental formula

  • Maxilla I1I2I3CP1P2P3P4M1M2
  • Mandibula I1I2I3CP1P2P3P4M1M2M3
  • Carnassial teeth p4andM1
    red: single rooted, green: double rooted, blue: triple rooted

Mandible

  • Consists of body with dentition and mental foramina and ramus with temporomandibular joint, coronoid process & mandibular foramen for mandibular nerve, vein and artery Skull normal mandible - radiograph intra-oral VD.
  • Intermandibular symphysis is a synchondrosis.

Temporomandibular joint

  • Condylar joint with transversely elongated mandibular condyle articulating mandibular of temporal bone Skull mesaticephalic 01.
  • Joint surfaces should be smooth and slightly widened ventrally.

Cranial vault

  • The brain case comprises 14 flat bones - 8 paired and 6 unpaired.
  • Suture lines are clearly visible between the flat bones and should not be mistaken for fractures.
  • The bones have a dimpled 'copper-beaten' appearance.
  • There is marked variation in shape of the cranial vault, eg toy breeds often have domed skull.
  • In some dogs the fontanelle remain open permanently.

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 rhinits, FB, viral, bacterial and allergic rhinitis.

Chronic hyperplastic rhinitis

  • Usually bilateral.
  • Diffuse, ill-defined increase in opacity with blurring of turbinates and conchae Skull chronic hyperplastic rhinitis - radiograph intra-oral.
  • 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 nasal aspergillosis - radiograph intra-oral (usually caused by aspergillosis Nasal aspergillosis/penicillosis ).
  • 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.
  • Does not cause septal deviation.

Nasal foreign body

  • Usually lucent, eg grass awn.
  • May see focal rhinitis characterized by focal soft tissue/fluid opacity with minimal turbinate destruction Skull nasal foreign body - radiograph intra-oral.
  • Septum and bony case will be unaffected.

Rhinitis

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

Nasal neoplasia

  • Cannot differentiate types radiographically.
  • Increased soft tissue opacity combined with destruction of ethmoturbinates and nasal conchae Skull nasal neoplasia - radiograph intra-oral.
  • Usually unilateral initially but in later stages affect both sides.
  • Often cause bowing and erosion of vomer/septum.
  • 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 Skull: frontal bone neoplasm - radiograph lateral.
  • Sinus may appear normal on lateral but DV or rostrocaudal oblique projection shows loss of gas opacity Skull: frontal bone neoplasm - radiograph skyline.
    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.

Nasal fractures

  • Often depressed and may need oblique projections to highlight fracture lines Skull frontal bone fracture - radiograph lateral oblique.
    Should all be considered open fractures.

Lysis of frontal bone

  • Neoplasia:
    • Often very aggressive with severe bone lysis Skull tumor - radiograph lateral oblique.
    • May arise within sinus or extend from adjacent tissue Skin flap 03 recurrent intermediate mast cell tumor over frontal region.
    • Osteoma and multilobular tumor of bone may present as cauliflower-like growth of new bone arising from surface of frontal bone with no lysis.
  • Aspergillosis Nasal aspergillosis/penicillosis :
    • Often multiple punctate lucencies.
    • Lumen often gas-filled but may be soft tissue opacity due to fungal granulomas.
  • Osteomyelitis Osteomyelitis :
    • Usually secondary to tumor.

Craniomandibular osteopathy 

  • Marked bilaterally symmetric periosteal new bone formation along mandibular margins Craniomandibular osteopathy Skull mandible craniomandibular osteopathy - radiograph lateral.
  • Thickening of petrous temporal bone (including tympanic bulla).
  • May be associated with additional thickened frontal and calvarial bones, and antebrachial periosteal reaction.
  • May cause temporomandibular ankylosis.
  • Primarily seen in West Highland White, Cairn and Scottish terrier, occasionally in other medium to large breed dogs.
  • Differential diagnosis includes osteomyelitis, malunion fracture, neoplasia: usually unilateral or asymmetric changes, which usually also include a lytic component in neoplasia and osteomyelitis.

Mandibular and maxillary osteopenia

  • Caused by chronic hyperparathyroidism (primary, secondary, tertiary).
  • Radiographicaly visible as diffuse loss of alveolar bone, giving the impression of floating teeth Skull renal secondary hyperparathyroidism - radiograph DV (oblique) Skull renal secondary hyperparathyroidism - radiograph lateral oblique.

Oral and dental neoplasia

  • Most oral neoplasms are predominantly lytic and may also have some additional irregular new bone formation Skull dental tumor - radiograph intra-oral. Radiographic differentiation often not possible.
  • Squamous cell carcinoma, fibrosarcoma, malignant melanoma, are most common malignant oral soft tissue tumors and can not be differentiated radiographically.
  • Mandibular osteosarcoma and multilobular osteochondrosarcoma (= chondroma rodens) are most common malignant bone tumors. The latter is characterized by multilobulated dense new bone formation on the surface of flat bones of the skull and mandible.
  • Dentigerous cysts, ameloblastoma, adamantinoma, odontoma and fibromatous, ossifying epulis are the most common benign oral and dental neoplasms. Characterized by expansile lytic mandibular or maxillary lesion with more or less well defined margins.
  • Acanthomatous epulis is a histologically benign but radiographically aggressive lesion (lytic with irregular margins).

Other oral and dental disorders

  • Dental anomalies in size, shape and number of teeth are common. Dental radiographs made at young age can help determine the presence of crowns prior to eruption Skull normal teeth - radiograph intra-oral DV Skull dental disease (lytic halo) - radiograph lateral oblique Skull dental retentionpolydontia - radiograph intra-oral.
  • Periodontal disease and tooth root infection can be recognized radiographically as widening of the lucent periodontal space and horizontal loss of alveolar bone, periapical lucencies, pathologic tooth root fractures.

Auralpathology
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 Skull calcification of ear canal - radiograph DV.
  • Mild mineralization with normal luminal diameter is an incidental finding in older dogs.
  • 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.
    Soft tissue, eg tongue superimposed over bullae on oblique view can mimic lack of aeration.
  • Lysis - neoplasia Skull tympanic bulla tumor osteomyelitis - radiograph lateral oblique or osteomyelitis.
  • Thickening of wall with infection Skull tympanic bulla tumor osteomyelitis - radiograph lateral oblique.
    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 open-mouth.
  • 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.

Orbital 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.

Orbital 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 or tissue in enamel in some cases.

Temporomandibular joint

  • Jointshould be evaluated as for appendicular skeletal joints Skull normal temporomandibular joint - radiograph oblique.
  • Conditions affecting joint are the same as other synovial joints, eg trauma Skull temporomandibular joint trauma - radiograph sagittal oblique.

Temporomandibular osteoarthritis

  • Osteophyte formation as retroarticular process.
  • May see irregularities of joint surfaces in severe cases.
  • Shallow mandibular fossa and flattening of condyles seen with dysplastic joints Skull temporomandibular joint trauma - radiograph sagittal oblique.

Subluxation of TMJ

  • Helpful to take radiographs with open or closed.
  • In Basset hounds with jaw-locking the coronoid process of mandible impinges on zygoma on DV projection.

Destruction of TMJ

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

TMJ fractures

  • Often concurrent luxation of TMJ.

TMJ ankylosis in 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 Skull frontal bone fracture - radiograph lateral oblique.
    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 Skull hydrocephalus - radiograph DV.
    Breeds predisposed to hydrocephalus may normally have dome-shaped skulls.
  • MRI is the best method for evaluating intracranial disease.

Neoplasia

  • Variable appearance depending on type:
    • Multilobular osteochondrosarcoma-  characteristic granular, mineralized, stippled appearance 'broccoli pattern'. May be associated lysis of underlying bone.
    • Osteoma - benign tumor with no lysis and dense periosteal new bone.
    • Chondrosarcoma Chondrosarcoma or osteosarcoma Osteosarcoma: axial skeleton - variable lysis and perisoteal new bone. Tend be more clearly defined than appendicular bone tumors with organized new bone formation.

Craniomandibular osteopathy

  • May affect parietal bones with cortical thickening and smooth periosteal new bone.

Additional studies

Ultrasonography

  • Limited value in evaluating skull lesions with the exception of orbital disease.
  • May allow differentiation of retrobulbar cellulitis, abscess and neoplasia.
  • May be needed to evaluate certain brain disorders, notably hydrocephalus Hydrocephalus , if the fontanelle remain open.
  • Evaluation of the tongue and other soft tissues has been described but is of little clinical value.

Scintigraphy

  • Scintigraphy has previously been used to investigate brain disorders, especially neoplasia but has been superceded by CT and MRI.

MRI

  • The technique of choice for intracranial disease and most diseases affecting soft tissue of the head.
  • It allows multiplanar scanning and gives unparalelled soft tissue contrast.
  • In addition to CNS disease it is invaluable for presurgical planning of skull tumor surgery and investigation of nasal and orbital disease.

CT

  • The method of choice for evaluating bony disease in the head.
  • Allows high resolution, cross-sectional images and 3-D reconstructiion which allows the true extent of complex lesions to be evaluated.
  • It may also be preferred to demonstrate intracranial hemorrhage.
  • CT allows reasonable evaluation of the soft tissues and brain but is inferior to MRI for most lesions.