Imaging of the Eyes & Orbit, Brain

sihirlifil's version from 2017-10-26 00:15

Eyes & Orbit

Question Answer
What is Radiography good for?Overview
Presence of ST swelling, bone destruction, radio-opaque foreign bodies
What is Ultrasound good for?Mass identification, perfusion (doppler) of eye & retrobulbar space
Fluid accumulation, FB
Option of US guided FNA & biopsy
What is CT good for?Overview, extent of lesion
Involvement of bone/TMJ, lymph nodes, brain
Presence of FB
Option of contrast studies & biopsy & thoracic scans for met check (can look at slice by slice, different planes)
What is MRI good for?Involvement of the BRAIN, inner/middle ear
Extent & characteristics of tissue, presence of fluid, FB
Option of contrast studies
Retrobulbar/orbital disease: CSExopthalmus, blepharospasm, chemosis, swelling of affected orbit & associated soft tissue
Retrobulbar/orbital disease: causesRetrobulbar cellulitis & abscesses (sinusitis, tooth root abscesses)
Neoplasia (retrobulbar, optic nerve)
Radiography of orbit: what can be seen?Only the contours of the bony orbit (zygomatic bone, zygomatic process of temporal bone), St swellings in region of orbit, and radiopaque FB
Need at least 1 lateral and 1 DV/VD, additional lesion-oriented projections
Ultrasound of the orbit: when?Visual inspection of the eye impaired by swelling, opacification, miosis, intraocular hge/debris
Ultrasound of the orbit: how is it done?In conscious or sedated animal
With high frequency transudcer directly on the cornea (use topical anesthesia) or through closed eyelids (poorer image quality)
Scan in horizontal and sagittal planes, examine globe & retrobulbar tissues
Ocular ultrasound: globe diameter?Approx 2 cm, spherical
Ocular ultrasound: Cornea?Parallel set of lines
Ocular ultrasound: can you see the anterior chamber?Yep (anechoic)
Ocular ultrasound: Lens2 parallel, curved, hyperechoic lines representing anterior & posterior surfaces of lens
Body of lens is anechoic~
Ocular ultrasound: Iris/ciliary bodyPeripheral, echogenic, vascularized
Ocular ultrasound: vitreousAnechoic
Ocular ultrasound: retina?Can see it, and dx retinal detachmetn
Ocular ultrasound: optic discSmall depression/elevation on posterior wall of globe
Ocular ultrasound: Retrobulbar space contains what?Ocular muscles
Optic nerve
Retrobulbar fat
Zygomatic salivary gland
What are the arrows pointing at, from top to bottom? (canine eye)
Anterior chamber (anechoic)
Iris (echogenic, peripheral, vascularized)
Posterior wall of lens (curved, hyperechoic)
Vitreous (anechoic)
What's happening in this US? (yes ik there are words...)
FB in retrobulbar space
HYPERECHOIC and casts acoustic shadow
How does retinal detachment look on US?Hyperechoic band of tissue separated from the choroid, mayby undulating (layer of tissue elevated from back of posterior wall)
Converges at optic disc (fixed attachment of retina)
What is the *?
Attachment of the retina to the Optic disc (fixed!)
Retinal detachment
Can happen to various degrees, different appearance
Arrow = ?
Intraocular mass
Can use US to guide FNA
Ocular mass in a horse
Retrobulbar mass in a dog
Deeper view, probe placed on eyelid, globe not a nice round shape
What's going on in these transverse CT? (left bone window, right ST)
Normal :) at level of orbits
What's going on in these transverse CT? (ST window)
Extensive ST swelling in orbital region = abscess (yellow arrow)
How can we tell if tissue is diseased or healthy based on CT?Attenuates differently! (also different shape, size etc)
* = ? What's going on?
Retrobulbar abscess 2ry to FB
* = abscess cavity (pus can be aspirated here)
* = ? Arrow = ? What's going on?
Dog with Optic meningioma (*)
Partially mineralized, causing exopthalmus and bone atrophy (arrow) of bony wall between orbit & frontal sinus


Question Answer
Hydrocephalus = Distension of the lateral ventricles
What's special about dx hydrocephalus?One of the few intracranial diseases that may be imaged with RADIOGRAPHY!
Hydrocephalus congenital in who?Yorkshire Terriers
Hydrocephalus: radiological signsDoming of cranial vault
Thinning of calvaria
Homogenous appearance of calvaria due to loss of internal convolutional markings
Persistent fontanelles (discontinuous skull bones)
Arrow pointing to?
Persistent fontanelles (discontinuous skull bones) seen in hydrocephalus
Hydrocephalus in 7 week-old Staffordshire puppy
Homogenous opacity, loss of structured appearance, ventricles extend & cause pressure
For who can you use US to diagnose hydrocephalus?Very young animals
Toy breeds with incomplete closure of sutures of skull bones
(Use bony defect(s) as sonographic window)
Anechoic arrows? Middle arrow? (what modality)
Anechoic = Fluid-distended lateral ventricles
Middle echoic = Residual brain tissue
Arrows? (what modality?)
MRI transverse T2
Top arrow = Fluid in distended lateral ventricles (CSF is hyperintense)
Bottom = Residual brain tissue (minimal)
CT techniques for imaging the brain: what happens after IV contrast medium injection?(Angiography or dual phase contrast studies)
After IV CM admin, intracranial organs outside the BBB will ENHANCE
Which specific organs enhance after IV contrast?Pituitary gland
Choroid plexus
Blood vessels
If a lesion accumulates CM, what does that mean?Vascularization and disrupted BBB! (eppendymal layer perfused)
Intra-axial lesion = Originated from within brain parenchyma
Extra-axial lesion = Originated from outside the brain parenchyma
Which is better for ST contrast, CT or MRI?MRI
What is CT excellent for? why?Trauma
Can ddx between bone & hemorrhage
Good way to detect acute vs. infarct
What special thing can you do to post-process CT images in general? Good for what?3D surface rendering reconstructions
Good for surgical planning
Fracture of left frontal bone & zygomatic process
(3D surface reconstruction)
Fractured RIGHT > left parietal & frontal bones in a chihuahua
How can intracranial hemorrhage appear?Intra- or extraparenchymal, or in liquor (fluid) space
CNS trauma: how does age of a hematoma affect the CT image?Changes attenuation values (HU)
Cerebral hemorrhage in a foal
What is the difference between these 2 images?
(CT of meningitis in canine brain)
Left = pre-contrast
Right = post-contrast with peripheral enhancement pattern (can see lateral ventricles b/c fluid less attenuating than brains. Gyra, sulci can be seen with contrast as blood vessels take it up)
Hyperintense signal shown by the meninges (taking up contrast)
Much more evident than in CT!
What is the contrast medium for MR?Gadolinium
Meningioma in a cat, pre & post conrast (intra-axial tumor)
Brain masses (intra-axial tumors)
Condition? Which planes?
Pituitary gland adenoma (CSF hyperintense signal)
T2 weighted transverse (left), T1 sagittal post-Gadolinium (middle), T2 dorsal (right)
Condition? describe lesions
Hypophyseal tumor and brain/meningeal metastases
T1 post contrast administration: Multiple hyperintense nodular lesions along the meninges and in cerebellum/brainstem compatible with metastases. Moderate hydrocephalus. (Multiple contrast-accumulating lesions)
MRI of Meningioma in cat
Typical appearance: Large mass, broad-based towards calvaria, tail joins up with meninges. Takes up contrast well