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Skull – general

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Abstract

Indications for skull imaging mainly involve investigation of clinical signs relating to different parts of the head, but in some cases systemic metabolic disease affecting bone may be best seen in the skull. Typical clinical signs include: congenital anomalies of the head; deformity, swelling or discharging sinus; trauma to the head area; problems with jaw movement, including open-mouth jaw locking; suspected metabolic disease which may involve the skull; postsurgical complications; and neurological dysfunction. This chapter covers radiography, alternative imaging techniques and abnormal imaging findings.

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Figures

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17.1 Positioning for a lateral view of the skull of a dog. A radiolucent foam wedge has been placed under the nose and rostral mandible in order to achieve accurate skull positioning.
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17.2 Normal lateral skull radiograph of a German Shepherd Dog.
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17.3 Positioning for a DV view of the skull of a dog. The cassette has been slightly raised from the table on a small rigid box.
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17.4 Positioning for a VD view of the skull of a dog. The dog is restrained in symmetrical dorsal recumbency using a rigid trough and sandbags.
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17.5 Normal DV skull radiograph of a Labrador Retriever.
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17.6 Positioning for a lateral oblique (Le30V-RtDO) radiograph of the skull in a dog. From the lateral position the head is rotated towards the VD position in order to skyline the side closer to the cassette. Rotating the head towards the DV position is used to profile the dependent frontal sinus.
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17.7 Normal oblique lateral view of a tympanic bulla in an English Springer Spaniel. Note that this view is generally unsatisfactory for the TMJ (see Figures 17.8 and 17.9 ) owing to obliquity of the joint.
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17.8 Positioning for the sagittal oblique view (Le20R-RtCdO) for the right TMJ. Elevation of the nose brings the TMJ that is closer to the table into a vertical position so that the joint space can be seen clearly.
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17.9 Normal appearance of the TMJ on a sagittal oblique view.
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17.10 Positioning for the RCd view of the frontal sinuses and cranium, using a Perspex positioning frame. A greater degree of flexion is required to profile the cranium than the frontal sinuses.
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17.11 Normal appearance of the frontal sinuses on an RCd view.
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17.12 Positioning of the head for the open-mouth RCd view of the tympanic bullae. For the purposes of photography the endotracheal tube remained in place, although it is preferable to remove it before making the radiographic exposure in case of superimposition over the bullae.
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17.13 Normal appearance of the tympanic bullae on an RCd open-mouth view.
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17.14 Positioning of the head for the R10V-CdDO view of the tympanic bullae in a cat.
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17.15 Normal appearance of the feline tympanic bullae using the R10V-CdDO view. The bullae are projected caudal to the cranium and are, therefore, seen with less superimposition of other structures.
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17.16 Normal appearance of the skull and pharynx in a severely brachycephalic dog (Boston Terrier).
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17.17 Normal lateral skull radiograph of a cat.
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17.18 DV skull radiograph of a cat, which is essentially normal except for the absence of numerous premolars and molars.
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17.19 Ocular ultrasonography techniques. (a) The transcorneal scan in which the transducer is placed directly on to the cornea following the application of a topical anaesthetic. (b) The temporal scan in which the transducer is placed caudodorsal to the globe. (c) The zygomatic scan in which the transducer is placed ventral to the zygomatic arch. (Reproduced from , Chapter 2, Diagnostic imaging of the eye and orbit, in: )
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17.20 Ultrasonograms acquired using the techniques shown in Figure 17.19 . (a) Transcorneal approach, (b) temporal approach and (c) zygomatic approach. The anatomical structures visible in these images obtained from normal dogs are annotated. (Reproduced from , Chapter 2, Diagnostic imaging of the eye and orbit, in: )
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17.21 Normal CT scan of the nasal cavity of a dog at the level of the orbits. The image is optimized for bone.
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17.22 Normal MRI scan of the brain of a dog at the level of the TMJs. This is a T2W scan, i.e. fluid is bright.
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17.23 DV radiograph of a non-displaced cranial fracture in a Hungarian Vizsla that had fallen into a quarry. A narrow radiolucent line runs obliquely across the cranium and was not visible on other views. The dog was stuporous and blind, and MRI showed severe cranial contusion; however, the dog went on to make a full recovery.
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17.24 Transverse T2W MR image of the cranium of a 9-week-old Jack Russell Terrier puppy that had been bitten on the head by another dog and was showing neurological signs indicating left forebrain damage (falling to the right, right-sided menace deficit and right-sided conscious proprioceptive deficits). A depressed cranial fracture is seen, with abnormal hyperintense signal from the adjacent brain parenchyma and temporal muscle indicating oedema and haemorrhage, but there is no subdural haemorrhage. This puppy recovered with conservative treatment.
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17.25 Lateral skull radiograph of a 5-month-old Akita with a resolving subperiosteal haematoma over the frontal area. A thin, shell-like rim of new bone has formed over the haematoma; MR imaging showed the fluid contents.
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17.26 Severe congenital hydrocephalus in a 7-week-old Staffordshire Bull Terrier cross-bred puppy. The cranial vault is grossly enlarged, with a large open fontanelle and normal bony calvarial markings are absent. (Courtesy of the Minster Veterinary Practice, York)
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17.27 Transverse T2W MR image of a 4-year-old Lhasa Apso cross with seizures. There is massive dilatation of the ventricular system with corresponding thinning of cerebral parenchyma, due to hydrocephalus.
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17.28 Sagittal T2W MR image of the skull and cervical spine of a 2-year-old CKCS with occipital dysplasia and severe syringohydromyelia (‘Chiari’ syndrome). The caudal fossa of the skull is small, resulting in crowding of the foramen magnum by the cerebellum and brainstem. CSF in the ventricles and spinal cord appears bright on T2W images.
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17.29 Lateral radiograph of a cranial osteosarcoma in a 5-year-old cross-breed dog. A focal area of osteolysis with overlying shallow new bone production is visible in the dorsal midline but no information about possible inward extent is given.
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17.30 Transverse gradient echo MR image of the same dog as in Figure 17.29 . On this image, mineralized tissue is black. It can be seen that the osteosarcoma has completely breached the bone and is causing slight compression of the adjacent brain, although inward extent is much less than is often the case with such tumours. The lesion was surgically resected.
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17.31 CT scan (bone window) of the skull of a 7-year-old Canadian Shepherd Dog, diagnosed with a mass on the neurocranium. The image shows a mixture of aggressive osteolysis and unstructured new bone production, as well as asymmetrical soft tissue swelling. The final diagnosis was squamous cell carcinoma. (Courtesy of S Boroffka, University of Utrecht)
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17.32 RCd view of the cranium of a 12-year-old Domestic Shorthair cat with seizures. The left side of the calvarium (on the right of the image) is thickened and shows increased radiopacity compared with the right. MRI revealed a large meningioma with hyperostosis of the overlying bone.
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17.33 Idiopathic calvarial hyperostosis in an 11-month-old Bullmastiff bitch. The frontal, parietal and occipital bones are massively thickened and radiopaque, and the volume of the cranial vault appears to be reduced.
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17.34 Transverse T2W MR image of a 7-year-old CKCS with severe MMM. There is severe, asymmetrical, ill-defined hyperintensity and swelling of the masticatory muscles (temporal, masseter and pterygoid). The diagnosis was confirmed with muscle biopsy and serology for Type 2 muscle antibodies.
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17.35 DV skull radiograph of a 13-year-old cross-breed dog with neoplasia involving the right orbit and caudal nasal cavity (seen on the left of the image). The frontal sinus is opacified (*), which suggests either fluid trapping or tumour extension. Identifying such changes radiographically shows that the lesion is already extensive and that further imaging techniques are not necessary.
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17.36 Dorsal plane, contrast-enhanced T1W MR image at the level of the orbits, in a 12-year-old Labrador Retriever cross with exophthalmos. A discrete irregular mass is seen in one orbit, displacing the globe rostrally and compressing normal orbital fat (bright areas) and muscle (dark bands). The contralateral orbit is normal.
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17.37 CT scan (bone window) of the head of a 14-year-old female Patterdale Terrier cross with severe exophthalmos. An extensive soft tissue mass involves the orbit, frontal sinus and caudal nasal cavity and has resulted in severe aggressive osteolysis.
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17.38 Dorsal plane gradient echo MR image at the level of the ventral orbit/TMJ of a 9-year-old Labrador Retriever with exophthalmos due to an orbital myxosarcoma. In gradient echo images bone is of very low signal intensity (black) and hence osteolysis is clearly seen as disruption of the mandible and TMJ (compare with the opposite side). The soft tissue component of the myxosarcoma is a multiloculated cystic mass, which is seen as a hyperintense (bright) structure.
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17.39 Ultrasonogram of an orbital mass in a 10-year-old Domestic Shorthair cat with exophthalmos. A well defined, hypointense mass (*) is seen in the ventromedial part of the orbit, outlined dorsally by echogenic orbital fat.
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17.40 Dorsal plane fat-suppressed contrast-enhanced T1W MR image of the head of a 10-year-old Border Terrier with painful exophthalmos. The eye is displaced and severely compressed by a fluid-filled pocket in the medial aspect of the orbit, with marked contrast enhancement (inflammation) of surrounding tissue and ipsilateral temporal muscle. In addition, enhancement of local meninges is present, suggesting intracranial extension via the optic nerve, leading to meningitis.
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17.41 Lateral skull radiograph of a 4-year-old working Labrador Retriever that presented with severe ocular haemorrhage. Several pieces of lead shot are seen in the frontal area, although even with multiple radiographic views it is difficult to know whether any of them are within the eye. Ultrasonography would be required for this because metal objects produce artefacts with both CT and MRI.
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17.42 Sagittal oblique T2W MR image of the head of a 9-year-old English Springer Spaniel with acute head pain after running through a field. A piece of stick about 5 cm long is seen extending through temporal muscle caudal to the orbit. Optimizing image slice placement in an oblique plane permits the full size of the foreign body to be appreciated.
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17.43 Oblique DV view of the head of an English Pointer that had been kicked by a horse. Multiple fractures of the caudal maxilla and zygoma are seen, together with a fracture of the mandibular coronoid process and soft tissue emphysema.
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17.44 Rostral mandibular neoplasm in an 11-year-old Labrador Retriever. There is extensive destruction of both rostral mandibles with loss of five incisors and displacement of the remaining incisor and one of the canine teeth. Chaotic spicular new bone extends into an overlying area of soft tissue swelling. The histological diagnosis was acanthomatous epulis, although the radiographic changes are non-specific for tumour type.
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17.45 CT image (bone window) of the head of a 12-year-old Somali cat with a mandibular swelling. There is an aggressive expansile lesion affecting the mandibular ramus and causing mixed osteolysis and new bone production with some tooth loss. The final diagnosis was round cell tumour.
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17.46 Dorsal plane T1W MR image of a 6-year-old Labrador Retriever with a maxillary sarcoma. The caudal maxilla is expanded and there is some loss of teeth. The normal hyperintense signal intensity of bone marrow is replaced by tissue of lower signal intensity (compare with the opposite side). This loss of T1W signal is a sensitive way of detecting the extent of pathology but is likely to include surrounding oedema and inflammation as well as tumour tissue.
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17.47 Renal secondary hyperparathyroidism (‘rubber jaw’) in an aged Siamese cat with renal failure. There is reduced opacity and poor definition of the skull bones compared with the soft tissues, and the nasal turbinates are abnormally prominent. Dental loss may be related to age, but could also be the result of alveolar bone resorption.
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17.48 Craniomandibular osteopathy in a 4-month-old West Highland White Terrier. Florid periosteal new bone production is visible on the mandibles and tympanic bullae. This new bone is already starting to remodel, as it appears mainly solid, without the characteristic ‘palisading’ appearance.
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17.49 Cystic maxillary lesion in a 1-year-old Labrador Retriever with a facial swelling near the medial canthus of the right eye. A 15 mm diameter radiolucent structure with a fine bony wall is seen rostral to the orbit. Dacryorhinocystography has been performed and shows that the structure does not communicate with the nasolacrimal duct. The histological diagnosis was of epithelial cyst formation. (Reproduced from , with permission of the )
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17.50 3D surface-rendered CT image of the head of an Alaskan Malamute, showing a normal TMJ. 3D images can be manipulated to be viewed from any angle.
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17.51 Mildly displaced fracture of the retroarticular process of the TMJ in the same dog as shown in Figure 17.43 , an English Pointer that had been kicked by a horse and sustained severe zygomatic arch fractures. The TMJ fracture did not seem to be associated with clinical signs, although it may have predisposed the joint to degenerative change.
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17.52 TMJ dysplasia in a 1-year-old Irish Red Setter with open-mouth jaw locking. Although in this dog the retroarticular process appears of normal size, the rostral part of the mandibular fossa and condyle are slightly flattened (compare with the normal TMJ, see Figure 17.9 ).
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17.53 Soft tissue neoplasia (myxosarcoma) involving the TMJ of an 11-year-old Labrador Retriever with ipsilateral exophthalmos. The radiograph demonstrates osteolysis of the TMJ (arrowed).
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17.54 Middle ear disease in a 7-year-old Domestic Shorthair cat, caused by a large aural polyp. The affected tympanic bulla shows loss of normal aeration and the bulla wall is thickened owing to the presence of active periosteal new bone formation.
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17.55 CT scan (bone window) of a 9-year-old Flat Coated Retriever with chronic bilateral otitis externa. Both external auditory canals are occluded by soft tissue and in one bulla the normal air space is also obliterated by soft tissue. The bulla wall is slightly irregular. A contrast study showed that the bullar material was largely fluid in nature, and the diagnosis was otitis media. The inner ear structures within the petrous temporal bone appear normal.
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17.56 Transverse post-contrast T1W MR image of a 5-year-old Burmese cat with vestibular signs and ataxia. The image shows severe middle ear disease with intracranial extension, in the form of meningitis and abscessation ventrolateral to the brainstem. The bulla wall is interrupted.
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17.57 Transverse T2W MR image of an 8-year-old English Springer Spaniel with chronic otitis externa and recent signs of peripheral vestibular disease. The tympanic bulla is markedly expanded by heterogeneous soft tissue of medium signal intensity, which was found to be poorly contrast enhancing. The bulla wall appears to be intact. The inner ear structures are distorted but there is no visible intracranial or extrabullar extension. Following a bulla osteotomy the histological diagnosis was cholesteatoma.
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17.58 Nasopharyngeal mass in a 7-year-old Domestic Shorthair cat with stertor and nasal discharge. A discrete soft tissue mass is visible in the nasopharynx, outlined caudally by air. Although more commonly they are benign lesions arising in the middle ear, this mass was found histologically to be a lymphoma.
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17.59 Extensive, aggressive bone lesion affecting the tympanic bulla of an 8-year-old Golden Retriever, which was due to a ceruminous gland adenocarcinoma. The normal architecture of the bulla is completely lost and replaced by unstructured new bone over a wide area.
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17.60 Transverse post-contrast T1W MR image of a 3-year-old Domestic Shorthair cat with stertor and swelling ventral to the ear. The MR image shows a very large soft tissue mass obliterating the bulla lumen and ear canal and causing marked osteolysis. There are signs of otitis media in the opposite bulla, secondary to occlusion of the auditory tube by the mass. The histological diagnosis was adenocarcinoma.
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17.61 Parotid sialoliths in an 8-year-old CKCS with a large salivary mucocoele. A line of small, discrete, mineralized bodies is seen in the region of the parotid salivary duct. When removed surgically, they were found to be joined together as a serrated linear structure. (Reproduced from , with permission of the )

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