Exposure to teratogens (drugs that interfere with fetal development) in utero.Animal may arch its head back and extend all four legs.A large dome-shaped head (due to intracranial swelling).Acquired hydrocephalus can occur at any age. Acute onset of signs can occur with previously undiagnosed congenital hydrocephalus. Congenital hydrocephalus usually becomes apparent within a few week of birth, and up to a year of age. Acquired hydrocephalus can occur in all breeds. The congenital form is an inherited disease in Siamese cats.
It may also be caused by a tumor in the eye. Overproduction of spinal fluid can also cause hydrocephalus. The sites of obstruction include the interventricular foramina (channels that connect the paired lateral ventricles with the third ventricle at the midline of the brain), the mesencephalic aqueduct, or the lateral apertures of the fourth ventricle. It is caused by tumors, abscesses, and inflammatory diseases (including inflammation resulting from hemorrhage that has been caused by traumatic injuries or other causes of bleeding). This may result in considerable disruption of the architecture of the brain.Īcquired obstruction results in secondary obstructive hydrocephalus. Prenatal (before birth) infections may cause aqueductal stenosis (narrowing) with subsequent hydrocephalus. The most common site of obstruction is at the level of the mesencephalic (middle brain) aqueduct. However, clinical signs may be noted when intracranial pressure is normal.Ĭongenital obstruction causes primary obstructive hydrocephalus. Intracranial (within the skull) pressure may be high or normal. The meninges are composed of three membranous envelopes – the pia mater, which lies against the brain the arachnoid, the middle layer and the dura mater, the outer, thicker layer closest tot he skull – that surround the brain and spinal cord. In the case of obstructive hydrocephalus, spinal fluid accumulates due to an obstruction along the normal circulatory pattern (noncommunicating hydrocephalus), or the fluid accumulates at the fluid resorption site near the meningeal arachnoid villi (communicating hydrocephalus). This is ventricular dilation incidental to the primary disease. Intracranial (within the brain) pressure is a normal result. With compensatory hydrocephalus, spinal fluid fills the space where the nervous system’s functional parts have been destroyed and/or failed to develop. Both compensatory and obstructive hydrocephalus can be congenital (present at birth) or acquired. There are two types of hydrocephalus – compensatory and obstructive. It may involve the entire ventricular system (a set of hollow structures in the brain continuous with the central canal of the spinal cord), or only elements next to a site of ventricular system obstruction. The abnormal dilation may affect only one side of the brain, or both sides. In this case, the ventricles that are connected with the spinal cord are the ventricles that are being affected. Hydrocephalus is the abnormal dilation, or expansion, of the ventricular system due to an increased volume of spinal fluid.
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