A 1.5 year old neutered Labrador retriever, Rimadyl, presented to the Neurology Service at Tufts Foster Hospital for Small Animals for a two week history of neck pain. Rimadyl improved for about one week, however, clinical signs then progressed with an uncoordinated gait and dragging of all four legs.
Physical examination showed a dog in good general condition. The neurological examination revealed dull mentation, moderate ambulatory tetraparesis and ataxia, spontaneous knuckling on the right front leg when walking, an inconsistent menace reflex in both eyes, a strongly delayed hopping response in both forelegs, normal knuckling response in both hind legs and normal spinal reflexes. Palpation of the neck showed moderate discomfort. A multifocal condition affecting the neck and brain was suspected. Differentials included various causes of meningoencephalomyelitis, caudal occipital malformation syndrome with syrinx formation, hydrocephalus and, less likely, neoplasia.
An MRI study of the neck and brain showed marked enlargement of the lateral, third and fourth ventricles (Fig. 1-3). The mesencephalic aqueduct was patent. Based on these signal changes an increase in CSF flow through this area was suspected. Cortical white matter thickness was significantly reduced, the cerebellum appeared to be elevated, and the brainstem was flattened. An additional T2 weighted hyperintensity mainly over C1 and C2 but extending into the lower cervical spine indicated syrinx formation with surrounding edema.What is your diagnosis and what treatment options would you recommend?
The correct diagnosis is extra-ventricular obstructive hydrocephalus with secondary syringohydromyelia. The pathophysiology of this condition is not well understood. Outflow stenosis at the level of the lateral apertures of the fourthventricle or dysfunction of the arachnoid villi within the subarachnoid space are suspected. Underlying causes may include immune-mediated inflammation, congenital malformations or viral infections. Prior to treatment, intracranial pressure (ICP) was measured with an invasive Codman Express® system during general anesthesia. The mean ICP ranged from 18 to 30 mmHg (normal < 11 mmHg) prior to shunt placement. Spinal fluid analysis did not show any abnormalities. Due to the lack of a dome- shaped head, the progressive course, and the lack of an inflammatory CSF, a late manifestation of a congenital malformation was considered most likely.
Medical therapy is used to manage acute deteriorations or to delay surgery. Acetazolamide and Omeprazol are reported to reduce CSF production. Unfortunately, our experience has been that the beneficial effect is often short-lived and subsides after few weeks. Glucocorticoids are commonly used to treat veterinary patients. Despite the fact that some studies report a reduction in CSF production, other studies report conflicting data.The mainstay of treatment of hydrocephalus with increased ICP is ventriculo-peritoneal shunt placement. A large number of shunt designs are available to allow excess CSF to drain into the abdomen. Complications include shunt migration or occlusion, infection, and over-drainage of the brain. Rimadyl received a Codman shunt with a 5 mmHg pressure valve was implanted.
A CT scan after shunt placement confirmed proper positioning (Fig. 4, Figure 5). During the shunt placement the ICP normalized at 5-8 mmHg. The dog returned to normal neurological function (photo) and has done very well over the past year.