Computed Tomography

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Computed Tomography

• Lisa S. Ziemer, VMD, DACVR

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Goals

• What is CT?
• CT capabilities
• Indications for referral

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Computed Tomography

• Generates cross sectional images
• X-Rays are used for image collection
• Computer generates the images using data
  collected during the study

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Computed TomographyBasics
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CARES CT Inside
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Computed Tomography
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Computed Tomography
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Computed Tomography
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CT vs. Radiography

• Eliminates superimposition, allowing detection of
  lesions not visible on radiographs
• CT discriminates 2000 densities
• Radiography discriminates only five
• 3-D reconstruction is possible

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Viewing Images
Bone Window
Brain Window
CT gives you the ability to adjust the
brightness and contrast of the images, which
allows assessment of soft tissue and bone on the
same images.
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Iodinated contrast material in CT

• Intravenous iodinated contrast medium is commonly
  used in CT
• Increased uptake in highly vascular tissue
  neoplasia, inflammation
• Prolonged uptake in neoplasia or other areas with
  leaky vessels
• Also used for angiography, intravenous urography

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CT of the head

• Brain
• Nose
• Temporomandibular joints
• Middle ear
• Retrobulbar space

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CT Brain

• Indications
• Seizures
• Behavior changes
• Other neurologic deficits
• Differentials
• Congenital defects
• Trauma
• Inflammation
• Neoplasia
• Infarction

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Normal Brain
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Hydrocephalus

• Obstructive
• Congenital
• Acquired
• Non-obstructive
• Ex Vacuo

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Cerebrovascular Accident (CVA)

• Infarction
• Septic thromboembolism
• Neoplasia
• Coagulopathy
• Heartworm
• Idiopathic
• Infarction can be detected as early as 3- 6 hours
  after onset. Enhancement within 24- 48 hours
• Cerebral Hemorrhage
• Hypertension
• Neoplasia
• Vasculitis
• Coagulopathy
• CT extremely sensitive for acute hemorrhage.
  Enhancement 6 days- 6 weeks.

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Inflammatory Brain Disease

• Infectious
• Fungal
• Bacterial
• Protozoal (Neospora, Toxo)
• Viral (Distemper, FIV, FIP)
• Non-Infectious
• Breed Specific Encephalitides (Yorkshire,
  Maltese, Pug)
• Granulomatous Meningoencephalitis

Granulomatous Meningoencephalitis
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Brain Tumors

• Mass effect
• Falx Shift
• Ventricular Asymmetry
• Edema
• Contrast Enhancement
• Less sensitive than MRI for caudal fossa tumors
  and low grade neoplasms with insufficient
  contrast enhancement

Meningioma
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Pituitary Gland
Normal
Macroadenoma
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Choroid Plexus Papilloma
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139916/3y/MC/Labrador
Brain Metastasis

Choroid Plexus Papilloma

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Masticatory Muscle Atrophy
Trigeminal nerve sheath tumor
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Trigeminal Nerve Sheath Tumor
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CT Ears

• Indications
• Vestibular disease
• Chronic ear disease
• Differentials
• Otitis
• Neoplasia
• Polyps

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Normal Canine Middle and Inner Ear
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Normal Bullae
Feline
Canine
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Otitis MediaRadiography- 25 false negatives
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Otitis Media
Feline
Canine
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Aural tumors

• External ear canal neoplasia
• Ceruminal gland adenomas
• Ceruminal gland carcinomas
• Squamous cell carcinomas
• Primary middle ear tumors are less common

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Aural tumors

• External ear canal neoplasia
• Ceruminal gland adenomas
• Ceruminal gland carcinomas
• Squamous cell carcinomas
• Primary middle ear tumors are less common

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Nasal CT

• Indications
• Nasal Discharge/ Epistaxis
• Sneezing
• Pre-rhinoscopy or surgery
• Differentials
• Rhinitis
• Neoplasia
• Fungal infection
• Foreign body

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Normal Canine Nasal Cavity
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Normal Canine Nasal Cavity
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Rhinitis
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Canine Nasal Neoplasia
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Canine Nasal Neoplasia
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Nasal Aspergillosis
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CT Orbit

• Indications
• Exophthalmus
• Epiphora
• Differentials
• Neoplasia
• Abscess
• Granuloma
• Mucocoele
• Tear Duct Obstruction

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Retrobulbar Masses

• Typically present with exophthalmus
• Very difficult to diagnose radiographically
• Ultrasound is often helpful
• CT is ideal for imaging retrobulbar space
• DDx
• Neoplasia (particularly LSA and nasal tumors)
• Abscess
• Granuloma
• Mucocoele

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Retrobulbar Mass secondary to Nasal Neoplasia
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CT Temporomandibular Joint

• Indications
• Difficulty chewing
• Unable to open/ close mouth
• Pain with chewing
• Differential Diagnoses
• Fractures
• Ankylosis
• Neoplasia

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Normal Temporomandibular Joints
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Retroglenoid and Mandibular Condyle Fracture
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Fracture of the Retroglenoid Process
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Ankylosis of the TMJ
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CT Skull

• Indications
• Tumor margins
• Swelling
• Trauma
• Differentials
• Fractures
• Neoplasia
• Osteomyelitis

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Skull Fractures

• Can be very difficult to accurately diagnose with
  radiographs
• CT allows assessment for hematoma formation
• Acute hemorrhage is hyperdense (bright) on CT and
  is surrounded by vasogenic edema

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Left Sided Facial Swelling- Multilobular Tumor of
Bone
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Left Sided Facial SwellingPrimary Bone Tumor-
Feline
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CT Appendicular Skeleton

• Indications
• Elbow dysplasia
• Fissures / Fractures
• Bone tumor margins
• Questionable radiographic findings

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Elbow Dysplasia

• Fragmented Medial Coronoid Process
• Incomplete Ossification of the Humeral Condyle
• Osteochondritis Dissecans (OCD)
• Elbow Incongruities
• Ununited Medial Humeral Epicondyle
• Ununited Anconeal Process

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Fragmented Medial Coronoid Process

• Most common cause of elbow lameness in young dogs
• May or may not be a separate fragment
• Abnormal shape of MCP
• Fissures
• Radial incisure abnormalities
• Difficult to diagnose
• Non-displaced fragments
• Non-opaque fragments
• CT allows definitive diagnosis

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Fragmented Medial Coronoid Process
Left
Right
?
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Medial Coronoid Process88 vs. 23 sensitivity
(CT vs. radiographs)
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Image Reconstruction
Normal
FMCP
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Osteochondritis dissecans of the medial humeral
condyle

• Clinical signs similar to FCP
• Etiology
• Heritable genetic disease.
• Failure of enchondral ossification, cartilage
  fragmentation, subchondral sclerosis.
• Likely influenced by high energy diets and rapid
  growth.
• Difficult to diagnose small lesion,
  superimposition of olecranon

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Humeral Condyle OCD
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Incomplete Ossification of the Humeral Condyle

• Heritable condition in Spaniel breeds, rare in
  others
• Other forms of elbow dysplasia are rare in
  Spaniels!
• Two centers of ossification appear 22 days of
  age, fuse by 84 days
• Defect of bony fusion of medial and lateral
  ossification centers
• Difficult to diagnose radiographically
• Can lead to condylar fractures- 50 Y or T shaped

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Incomplete Ossification of the Humeral Condyle
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Opposite Limb
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Questionable or subtle radiographic findings
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CT Spine

• Indications
• Neurologic deficits
• Pain
• Differentials
• Fractures
• Disc disease / LS disease
• Neoplasia (vertebral, spinal, nerve root)

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Thoracolumbar Disc ProlapsePost Myelography
Normal
IVD Prolapse
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Intervertebral Disc Prolapse (Mineralized Disc)
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Spinal Fractures

• Radiography is inadequate to rule out vertebral
  fractures and subluxation in the acute canine
  spinal trauma patient. Radiography cannot
  reliably be used to detect compressive lesions.
  CT, where available, is therefore recommended in
  patients with a high clinical suspicion of such
  injury.
• Radiographs
• Fractures NPV 48
• Spinal cord instability NPV 35
• Sensitivity for all fractures 72
• Kinns, et al. Vet Rad and US, 2006.

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Spinal Fractures
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Lumbosacral Disease

• Lumbosacral Stenosis
• Congenital Malformation
• Inflammation
• Neoplasia
• Degenerative Changes
• Disc Herniation
• Ligamentous hypertrophy
• Vertebral DJD
• Spondylosis
• Instability

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Lumbosacral Disease
NORMAL
L7- S1 DISC PROLAPSE
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2- D Reconstruction
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Vertebral Tumor (Metastatic OSA)
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Peripheral nerve sheath tumors

• Nerve sheath tumors typically present with pain,
  neurologic deficits, muscle atrophy
• Very difficult to diagnose
• On CT may be very subtle thickening, or may be a
  large mass with extension into the spinal canal

C7 nerve root tumor post myelogram
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Brachial Plexus Tumor
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Brachial Plexus Tumor
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CT chest and abdomen

• Indications
• Mediastinum
• Neoplasia
• Cyst
• Abscess/ granuloma
• Lung interstitium
• Metastatic disease
• Primary tumors
• Lung lobe torsion
• Pleural effusion
• Thoracic Radiographs are indeterminate
• May change diagnosis in more than 50 of cases
• Liver / kidney Vascular anatomy
• Mass location and margins

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CT chest and abdomen

• Indications
• Mediastinum
• Neoplasia
• Cyst
• Abscess/ granuloma
• Lung interstitium
• Metastatic disease
• Primary tumors
• Lung lobe torsion
• Pleural effusion
• Thoracic Radiographs are indeterminate
• May change diagnosis in more than 50 of cases
• Liver / kidney Vascular anatomy
• Mass location and margins

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Normal Lung
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Pulmonary Metastatic Disease

• CT allows detection of nodules as small as 1 mm
• Pulmonary nodules not visible on thoracic
  radiographs until at least 7 mm
• Only 9 of metastases visible on CT were visible
  on radiographs (Nemanic, et al, JVIM, 2006)

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Primary pulmonary tumor with metastasis to
tracheobronchial LNs

• Primary pulmonary tumors commonly metastasize to
  the tracheobronchial lymph nodes
• CT 83 sensitivity and 100 specificity
  (Paolini, et al. JAVMA, 2006)
• Radiography did not detect TBLN enlargement in
  this paper

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Idiopathic Pulmonary Fibrosis of the West
Highland White Terrier
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Malignant Effusion/ Cavitated Pulmonary Mass
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Pulmonary Bulla
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Tumor margins

• CT is extremely useful for surgical planning
• Identify margins
• Determine whether a tumor is resectable/ assess
  for invasion into adjacent structures

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Conclusions

• CT is a very sensitive tool for a wide variety of
  organs and lesions.
• Best established head, elbows, spine.
• Increasing new clinical applications.
• Compared To MRI
• CT is excellent for bone lesions, nasal lesions
• Good for structural or mass lesions in the brain
• MRI is better for non-structural brain lesions
• With CT, only axial plane acquired (3 planes can
  be acquired with MRI)

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How do you get this done?

• For outpatient studies, call CARES and make an
  appointment for CT. Patient dropped off through
  the emergency service return home on the same
  day.
• For ongoing care or further assessment, make an
  appointment with a specialist (oncology, surgery,
  internal medicine, ophthalmology).
• Recent CBC/ CS (within 14 days) may be obtained
  by you or at CARES.
• CT reports will be faxed to your office the same
  day.
• Feel free to call any time with questions!

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Acknowledgements

• PetRad
• Rob McLear
• CARES
• BJ DiTullio
• Donna Steckley
• Jon Rappaport
• Bob Cohen