Dog Congenital Disorder

Dog Congenital Disorder, Caudal occipital malformation syndrome (COMS) is a congenital disorder in which the skull is too small to accommodate the brain. Consequently, the part of the brain nearest the neck, called the cerebellum, is pushed from its normal position and starts to exit the skull. This can lead to a buildup of spinal fluid, which puts pressure on the back of the brain and spinal cord, causing pain. Dogs with this syndrome scratch at their face and ears, thought to be due to pain from nerve compression.

Risk Factors

COMS is most common in Cavalier King Charles spaniels but is also seen in other small-breed dogs including:

  • Brussels Griffon
  • Chihuahuas
  • Maltese
  • Yorkshire terriers


While COMS is a congenital disorder or abnormality present at birth, clinical signs sometimes don’t appear until the dog is a few years old. These signs may include:

  • Neck pain
  • Weakness and lack of coordination
  • Irregular, constant scratching of the neck that’s not related to an underlying skin problem (phantom scratching)
  • Abnormal curving of the spine (scoliosis)
  • Loss of balance
  • Face muscle paralysis


Diagnosis requires an MRI, but breeds known to suffer from COMS may be treated with pain medications and other drugs to decrease fluid accumulation before performing an MRI.


Medications can help reduce fluid production in the brain and decrease pain associated with COMS.  Drugs commonly used to decrease fluid production include anti-inflammatory drugs and antacids. While medications can control the condition for dogs with mild signs of COMS, cases with moderate to severe signs often don’t get adequate relief with medications alone. In those case, surgical treatment may be recommended. The goal of surgery is to relieve brain compression and restore normal fluid flow.


There is no way to prevent COMS, but early detection makes treatment easier. If you have a Cavalier King Charles Spaniel or another small breed, keep an eye out for the signs.

By The Animal Medical Center