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1

DISORDERS AFFECTING THE CAUDAL FOSSA

• Degenerative

• Anomalous

• Metabolic

• Neoplastic

• Inflammatory/infectious

• Ischemic/vascular

• Traumatic

• Toxic

CHARACTERISTIC FEATURES OF CAUDAL FOSSA

DISORDERS

• Vestibular dysfunction

• Motor dysfunction

• Proprioceptive

dysfunction

• Cranial nerve V-XII

dysfunction

• Impairment of

consciousness

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CHIARI-LIKE MALFORMATION IN DOGS

• Many breeds, CKCS most

prevalent

• Similar to Chiari Type I of

humans

• Often associated with

syringomyelia

• Medical and surgical

therapy options

CHIARI MALFORMATION IN DOGS-RECENT OBSERVATIONS

• Entire skull may be abnormal vs

caudal fossa region alone

• Abnormalities of C1 and C2 also

identified in some dogs

• Some dogs have MRI evidence of

“disease” with no clinical signs

• Some abnormalities better

appreciated with CT (3D

reconstructed)

SURGICAL TREATMENT OF CANINE CHIARI MALFORMATION

• Foramen magnum decompression

(FMD)

• Infratentorial approach

• Similar to procedure in people

• Rationale of procedure

• Variations on the theme

• Personal experience and

recommendations

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FORAMEN MAGNUM DECOMPRESSION (FMD)

WITH CRANIOPLASTY

• Technically demanding

• Successful in most cases

• Controversial in veterinary medicine

• Large data set available at LIVS

TERMINOLOGY: WHAT DOES “CHIARI-

LIKE” MEAN?

• Confusing

• Probably not all Chiari

malformations

• Multiple other disorders in

the regions becoming

evident

• More descriptive

terminology needed

PATIENT POSITIONING

• Crucial for access to ventral limit of

supraoccipital bone

• Head should be flexed at a 90◦ angle

• If flexion insufficient at surgery, use

stay suture in caudal temporalis

musculature

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SURGICAL APPROACH-SUPERFICIAL

• Dorsal midline incision

• Landmarks are external

occipital protuberance and

dorsal spine of C2

• Superficial dorsal cervical

musculature-stay on midline

(median raphe)

DEEPER MUSCULATURE

• Biventer cervicis

• Rectus capitis

dorsalis

• Dissection off of C2

spinous process

BONE EXPOSURE

• Occiput

• Dorsal arch of C1

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CONTROL OF HEMORRHAGE

• Bipolar cautery

• Bone wax at lateral limits

of occipital exposure

• Surgicel

BONE DRILLING

• Very thin over occiput

• Thicker over C1

• Very dense connective tissue

between

• Do occipital region first

THINGS NOT TO DRILL

• Transverse sinuses

• Confluens sinuum

• Cerebellum

• Medulla

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INCISING THE MENINGES

• Head first

• New #11 blade

• At craniocervical junction-

tricky part

MENINGES INCISED-NOW WHAT?

• Graft-not a good idea

• Gelfoam-not a good idea

• Fat-not a good idea

• Marsupialization-who

knows?

• Meningeal resection

• Cauterization of band

remnants

WOUND CLOSURE

• Routine

• Interrupted pattern

• Subcuticular

interrupted

• Tissue glue

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TITANIUM/PMMA PLATE

• “Titanium” sounds cool

• Not why we use it (well, not the

main reason)

• “the mesh”, “the plate”, etc

• Purpose

BACKGROUND FOR THE TITANIUM/PMMA PLATE

PROCEDURE

• Modeled after procedure

successfully used in people

• Drastic reduction of post-

operative scar tissue

compression at FMD site

• 3D reconstructions looked cool

OVERVIEW OF TITANIUM MESH/PMMA PLATE PROCEDURE

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PLACING TITANIUM ANCHOR SCREWS

• 1.1 mm drill bit for guide holes

• May hemorrhage-plug with bone wax

or a screw

• Self-tap 1.5 mm x 6 mm screws

(about ½ way in)

• Nice to have Anspach drill vs

minidriver for this

• Newer “self-drilling” screws preferred

PREPARING THE MESH

• Cut with suture scissors

• Bend into convex shape

• Flare the caudal aspect

dorsally

• Notch the top to place on an

anchor screw

MAKING THE PLATE

• Wait until PMMA no longer

sticky

• PMMA on both sides of mesh

• Overlap of PMMA beyond

mesh

• Move quickly

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POST-OPERATIVE APPEARANCE

• Radiographs

• Reconstructed CTs faster

and more informative

• Can me re-MRI’d in

future, if necessary

ADVANTAGES VS. DISADVANTAGES OF PLATE

PROCEDURE

• Difficult, requires learning curve

• More prolonged post-operative pain

management

• Longer hospitalization

• Slightly more expensive (hardware)

• Appears to decrease disease

recurrence

QUICK REVIEW OF VENOUS SINUS LOCATIONS

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COMPONENTS OF THE CRANIOCERVICAL

JUNCTION

• Basiocciput

• Foramen magnum

• Atlas (C1)

• Axis (C2)

CRANIOCERVICAL JUNCTION

ABNORMALITIES (CJA)

• Umbrella term used in humans

• Subheadings include occipital, atlas, and axis malformations

• Also combinations of abnormalities

REASON FOR NEW TERMINOLOGY

• Makes inherent sense

• Underscores variety of possible disorders in this region

• Emphasizes need for complete imaging studies in these cases

• Emphasizes the need to individualize surgical plans

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• 3-yr-old MC

Pomeranian

• Severe pain-

apparently cervical

• Screaming episodes

throughout the day

SKIDDIE

• Syrinx over C3 and cranial thoracic spine

• Some flattening of cerebellum

• Overlap of dorsal arch of C1 and dorsal aspect of foramen magnum

SKIDDIE’S IMAGES

SKIDDIE’S SURGERY

• Foramen magnum

decompression

• Fixation of C1 to occiput

• Cranio/laminoplasty

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• Probably a variant of basilar

invagination/impression

• Varying levels of severity

• Very challenging disorder

ATLANTO-OCCIPITAL OVERLAPPING

(AOO) IN DOGS

OTHER CYSTIC CAUDAL FOSSA ABNORMALITIES

• Choroid plexus cyst

• Dermoid cyst

• Epidermoid cyst

NEOPLASIA OF THE CAUDAL FOSSA

• Meningioma

• Glioma

• Choroid plexus tumor

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NEOPLASIA OF THE CAUDAL FOSSA

• Surgery-often not

viable

• Radiation therapy

• Chemotherapy

• Supportive therapy

INFLAMMATORY DISORDERS OF THE CAUDAL

FOSSA

• GME

• Necrotizing leukoencephalitis

• Infectious disease

INFLAMMATORY DISORDERS OF THE CAUDAL

FOSSA

• GME treatment

• NLE treatment

• Infectious disease

treatment

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QUESTIONS