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156 Chiari-like Malformation

• Due to cross-sensitization, a positive • Cheyletiellosis has zoonotic potential. Try to SUGGESTED READING
limit direct contact with the affected animal.
intradermal skin test result for the house • Hospital environment should be Miller WH Jr, et al: Muller & Kirk’s Small animal
VetBooks.ir cheyletiellosis. Within a few months after Client Education AUTHOR & EDITOR: Manon Paradis, DMV, MVSc,
dust mite is seen in ≈50% of dogs with
dermatology, ed 7, St. Louis, 2013, Saunders, pp
decontaminated.
300-303.
mite eradication, all clinical signs resolve,
and intradermal reactions to house dust
mites are generally negative. This illustrates Humans transiently infected with Cheyletiella DACVD
the importance of ruling out cheyletiellosis spp mites may develop an uncomfortable,
before testing for atopic dermatitis. pruritic papular eruption, especially on
the arms, trunk, and buttocks. This should
Technician Tips spontaneously resolve within 3 weeks when
• Collect scales from exam table and examine the mites are eradicated from the animals and
with a magnifying glass or microscope at low the environment. Persistent symptoms should
power. prompt the person to consult with a physician.

Chiari-like Malformation Client Education
Sheet

BASIC INFORMATION • Malformations that can occur in association overcrowding within the caudal fossa.
or concurrently with CLM: hydrocephalus Overcrowding results in cerebellar herniation
Definition or intracranial arachnoid cyst and compression of the cervicomedullary
A congenital condition characterized by • Primary secretory otitis media (PSOM): a junction, which can lead to abnormal
decreased volume of the caudal fossa of the condition of Cavalier King Charles spaniels in cerebrospinal fluid (CSF) dynamics and
skull relative to the brain parenchyma, with which mucus accumulates within the middle subsequent SM in the spinal cord.
herniation of cerebellum through the foramen ear causing partial or complete hearing loss. • Over time, the meninges can hypertrophy
magnum and subsequent crowding of the Some patients will have concurrent vestibular at the cervicomedullary junction, leading to
cervicomedullary junction signs such as a head tilt or resting nystagmus, exacerbation of syrinx formation.
and others are clinically unaffected.
Synonyms DIAGNOSIS
Chiari-like malformation (CLM), caudal occipi- Clinical Presentation
tal malformation syndrome (COMS), occipital HISTORY, CHIEF COMPLAINT Diagnostic Overview
bone hypoplasia, Chiari type 1 malformation, • Early on, clinical signs can be intermittent A diagnosis of CLM is strongly suspected based
occipital malformation and tend to occur during times of excitement on the patient’s breed and presenting clinical
or stress. signs. To ascertain an accurate diagnosis and
Epidemiology • Patients present with a variety of clinical rule out other differentials, MRI of the head
Affects dogs (less often, cats) of either sex. manifestations. and neck and CSF analysis are indicated. To
Age of onset for clinical signs varies. Age ○ Most common presenting sign is cervical fully evaluate extent of disease in the central
of affected dogs ranges from 6 months to pain; can manifest as phantom scratching nervous system, multiplanar (axial, sagittal, and
3 years, although it has been appreciated in of the neck region. dorsal) MRI of the head, cervical, thoracic, and
older dogs. ○ Neurologic signs localizing to a cervical lumbar spinal cord is recommended.
• Cavalier King Charles spaniel myelopathy and/or cerebellovestibular
○ Most commonly affected breed system are also frequently seen. Differential Diagnosis
○ Evidence of heritability; mode of inheri- • Intervertebral disc disease (IVDD)
tance not yet established but thought PHYSICAL EXAM FINDINGS • Meningoencephalitis
to be epistatic (influenced by many • General physical examination is usually • Vertebral anomalies
loci) normal. • Primary secretory otitis media
• Documented primarily in small breeds: • Neurologic examination usually indicates a
Brussels griffon, Chihuahua, Yorkshire terrier, cervical myelopathy (i.e., upper motor neuron Initial Database
Maltese terrier, toy/miniature poodle, pug, deficits in all four limbs), cerebellovestibular • Neurologic examination (p. 1136)
shih tzu, Pomeranian, Boston terrier, French dysfunction (head tilt, resting nystagmus, • CBC, chemistry panel, and urinalysis usually
bulldog, Pekingese, Havanese, papillon, Staf- circling, loss of balance, cerebellar/vestibular normal.
fordshire terrier, miniature Dachshund, and ataxia, intention tremor, loss of menace • Survey radiographs of cervical spine: to screen
miniature pinscher. response despite normal vision), or both. for other differentials (IVDD, vertebral
• Cats: reports in domestic short hair, Persian • Hallmarks for CLM are hyperesthesia (pain) anomalies)
and/or paresthesia (abnormal sensations) in
ASSOCIATED DISORDERS the head/neck region. Back pain has also Advanced or Confirmatory Testing
• Syringomyelia (SM), also called syrinx, is been documented. • Diagnosis of CLM is based on MRI find-
a fluid-filled cavity within the spinal cord. • Clinical signs such as scoliosis, weakness/ ings of caudal cerebellar herniation, bony
Theories have been proposed as to why collapse, deafness, and seizures have been compression of caudal cerebellum, medullary
syrinxes occur in patients with CLM but appreciated. kinking, and SM; midsagittal T2-weighted
none confirmed. A syrinx can occur in the MR image of most importance (p. 1132)
absence of CLM or in conjunction with Etiology and Pathophysiology • CSF analysis is often performed to rule out
another disease process affecting the spinal • Current theory: developmental abnormality concurrent inflammatory brain or spinal cord
cord (e.g., neoplasia, vertebral fractures). of the occipital bone resulting in intracranial disease (pp. 1080 and 1323).

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