Hydro=pertaining to water/fluid , and cephalus=pertaining to head (cranium).

Clinical Signs

May observe any of the following:

  • Head will be much larger than normal, out of proportion to body size, and noticed within the first weeks of life.
  • May observe seizures as condition progresses.
  • Poor motor coordination as condition progresses.

*Note: for information on recognizing various signs of pain or discomfort refer to: Signs of Pain In Rats.


Hydrocephalus is the result of an abnormal accumulation of cerebral spinal fluid in the ventricles of the brain, which causes the cranium/head to become enlarged. It can develop when there is congenital malformation that obstructs the flow and causes the fluid to accumulate.

Hydrocephalus is classified as communicating (or non-obstructive) or non-communicating (obstructed flow).

  • In communicating hydrocephalus, the obstruction is outside of the ventricle system of the brain, the flow is not blocked between the ventricles but rather the excess fluid accumulates in them because it is not able to be absorbed from the cerebral subarachnoid space.
  • In non-communicating hydrocephalus, the accumulation of fluid is blocked from some point in the ventricle system.

Hydrocephalus besides being a congenital defect can also be acquired by having fibrosis of the meninges (covering of the brain), as well as, obstruction caused by trauma, inflammation, cysts, neoplasms, or hematomas. This condition is ultimately the accumulation of cerebral spinal fluid as a result of a blockage in the circulatory path, or in the fluids overproduction.

In humans a surgical procedure can be performed for shunt placement to keep the cerebral spinal fluid from accumulating. However in rats shunt placement is not feasible.

Hydrocephalus in rats is primarily congenital in nature, and is typically a fatal condition depending upon severity. It is generally seen by the breeder within the first four weeks of life.

Some rats having a mild form of hydrocephalus can, and do, survive; however, seizure activity can be a complication of this condition as the rat ages requiring the rat to be on anticonvulsant medication for life.


Case Histories of Hydrocephalus

  • Fig. 1: Congenital Hydrocephalus in 4-week-old female rat
  • Fig. 2: Suspected Hydrocephalus in rat less than 3 months (Fraiser)
  • Fig. 3 Hydrocephaly in 4-month-old male rat
  • Fig. 4 Hydrocephaly in male rat (Chase)


Witnessed by head size and circumference out of proportion to body.

Exhibits failure to thrive.

Exhibits poor motor coordination.

Can be observed on CT scan.


Refer to the Rat Medication Guide for recommended dosages of dexamethasone, if needed, to reduce swelling of tissues.

Provide supplemental nutrition as needed.

If seizure activity is present, please review the article Seizures, in the Rat Health Guide section.

Nursing Care

  • Assist the pet rat with grooming if needed.
  • Provide assistance with feeding, if needed.
  • Provide for comfort and safety of cage environment.
  • When condition precludes further comfort or quality discuss euthanasia with veterinarian.


  • Free from injuries in cage environment or from cagemates.
  • Able to receive and tolerate nourishment.
  • Able to groom self or be assisted by owner.
  • Emotional support for those having to consider euthanasia for their rat.


  • In order to help prevent this condition from showing up in a litter breeders need to be aware of any predisposing genetic traits in their colonies.


Links to

Linked from


The Rat Guide and its affiliates accept no responsibility for misuse or misunderstanding of its information. This guide in whole or part, exists solely for the purpose of recognizing and understanding the care and illnesses in the pet rat. Please seek advice and treatment from a qualified Veterinarian if your rat is ill.

2000 - 2024 by Karen Grant RN. All rights reserved.
All other written and visual materials used by permission of specific authors for the sole use of the Rat Guide. Please visit our Privacy Policy for details.
Brought to you by KuddlyKorner4u
See Logos page for linking to the Rat Guide.
Contact us here: Rat Guide Team
Please note: Rat Guide email is not checked daily. Send e-mail to if you have an urgent medical problem with your pet rat. When possible, it is always best to take your rat to a qualified rat veterinarian.