Surgical Management of Combined Hydrocephalus, Syringohydromyelia, and Ventricular Cyst in a Dog

Introduction

New diagnostic techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) are useful for obtaining precise information about neurological diseases and have led to the accumulation of new knowledge about neurological disorders that afflict animals.^1–8 For example, syringohydromyelia, a rare disease in which fluid fills the syrinx cavity in the spinal cord, can now be diagnosed with either CT or MRI.^1,3,5,9–11 These examination procedures also facilitate the surgical treatment of some animals suffering from syringohydromyelia and hydrocephalus.^{2–4,6,12,13} The purpose of this report is to describe the clinical signs, clinical course, and surgical management by ventriculoperitoneal shunting of combined hydrocephalus, syringohydromyelia, and ventricular cyst in a dog.

Case Report

A 7-month-old, 4.4-kg, intact male miniature dachshund was referred to the Veterinary Teaching Hospital, Faculty of Agriculture, Miyazaki University, with gait abnormalities and altered mentation. Several days earlier, the dog ran away from home and was found lying on the road. Mental status at that time was depressed.

At presentation to the teaching hospital, the dog was weakly ambulatory and paraparetic. Head pressing was also observed, and postural reactions (e.g., proprioception, hopping, wheelbarrowing, hemistanding) were markedly delayed or slow in all limbs, especially in the right thoracic and pelvic limbs. Tactile and visual placing reactions were slow or absent. Deep sensation was partially absent in all limbs. Withdrawal reflexes were detected in all limbs, and patellar and triceps reflexes were exaggerated. Menace responses and pupillary light reflexes were weak in both eyes. Other cranial nerve responses were also weak. No spinal pain was detected. No other abnormalities were found on physical examination.

A complete blood count and biochemical profile were normal. Survey radiographs showed a thin calvarium with a smooth, ground-glass appearance. Nonsynchronized, high-amplitude slow waves (70 to 170 μv, 1 to 3 Hz; reference ranges of light sleep 75 to 100 μv, 4 to 6 Hz) were detected on electroencephalography (EEG) performed without sedation by a previously described method.¹⁴ Magnetic resonance imaging^a revealed severe dilatation of the lateral and third ventricles; a dilated mesencephalic aqueduct; a small brain stem; cystic dilatation of the fourth ventricle with extension into the cervical spinal cord to the second cervical vertebra; a small cerebellum; and syringohydromyelia in the cervical and thoracic spinal cord [Figures 1, 2]. Based on MRI findings, the diagnosis was hydrocephalus, syringohydromyelia in the cervical and thoracic spinal cord, and ventricular cyst. The MRI findings in this case have been briefly reported by Taga et al.⁵

The dog was initially treated with prednisone^b (1 mg/kg per os [PO] q 24 hours) and ampicillin^c (20 mg/kg PO q 12 hours) for 20 days. When clinical signs did not improve, surgical treatment with ventriculoperitoneal shunting was performed. Atropine sulfate^d (0.03 mg/kg subcutaneously) and flunitrazepam^e (0.1 mg/kg intravenously [IV]) were given as preanesthetic medications. Anesthesia was induced with thiamylal sodium^f (7 mg/kg IV) and maintained with isoflurane in oxygen. End-tidal carbon dioxide (CO₂) was maintained at 25 to 30 mm Hg to prevent intracranial hypertension. The dog was placed in sternal recumbency with the head elevated. A dorsal midline approach to the cranium was made.

Nonunion of the coronal suture was observed in the left cranium. The cerebrospinal fluid (CSF) pressure was 83 mm H₂O in the lateral ventricle, and no CSF abnormalities were found when analyzed. Because CSF pressure was within the reference range, an abdominal tube with a low-pressure valve^g was inserted as follows.¹⁴ A section of a ventricular tube for the CSF reservoir^h was inserted through the left side of the open coronal suture after puncturing the dura mater with an 18-gauge needle. A flat-bottom pumpⁱ was placed on the left caudal cranium and was connected to the drainage tube. The abdominal tube was also connected to the ventricular pump and tunneled under the subcutaneous tissues of the thorax and abdomen to be inserted into the abdominal cavity through the left flank. All muscles, subcutaneous tissues, and skin were closed routinely. The dog recovered from anesthesia uneventfully. The clinical signs dramatically improved, and the animal was normal within a couple of days. Prednisone was tapered and discontinued 2 weeks postoperatively.

Three months after surgery, altered mentation and neurological abnormalities similar to those seen at the first admission were observed. Survey radiographs revealed a broken ventricular drainage tube in the left ventricle. A second MRI was performed and revealed dilated ventricles, syringohydromyelia, and a ventricular cyst. A second operation was performed to reinsert a second ventricular drainage tube. The anesthesia and surgical approach were the same as for the first operation. A hole was made in the right side of the parietal bone using an orthopedic drill (3.5 mm) to allow insertion of the drainage tube.^j An L-shaped connecting tube^k was inserted into the ventricular drainage tube where it exited the hole in the bone. A modified drainage tube was then inserted using a procedure similar to that of the first operation, and it was connected to the ventricular pump already in place. The broken ventricular tube was not removed from the lateral ventricle. Clinical signs immediately improved after the second operation.

Magnetic resonance imaging was performed 8 months after the second operation, and results were dramatically different [Figures 3A, 3B, 4]. The dilatations of the lateral, third, and fourth ventricles and the mesencephalic aqueduct had decreased in size, and the thickness of the cerebral parenchyma and the brain stem had increased. The size of the cerebellum had increased, and extension of the cystic dilatation of the fourth ventricle and syringohydromyelia in the spinal cord had resolved. The tip of the ventricular drainage tube was seen in the right hippocampus, indicating the deep placement of the drainage tube [Figure 4].

Although no gait or mentation abnormalities were noted, 9 months after the second operation, the dog had a very mild seizure and the seizure recurred every 3 months. No treatment was instituted for these seizures. A cluster of tonic-clonic, generalized seizures occurred 25 months after the second operation. The dog was admitted to the hospital and was treated with phenobarbital^l (100 mg intramuscularly). Abnormal laboratory findings included elevated white blood cells (24,800/μL, reference range 6100 to 17,400/μL); decreased platelets (4.5 × 10⁴/μL, reference range 14.5 × 10⁴ to 44.0 × 10⁴/μL); elevated aspartate aminotransferase (AST, 105 U/L, reference range 10 to 50 U/L), alanine aminotransferase (ALT, 211 U/L, reference range 15 to 90 U/L), and creatine kinase (CK, 344 U/L, reference range 0 to 130 U/L); and mild hypokalemia (3.0 mEq/L, reference range 4.0 to 5.4 mEq/L). Nonsynchronized fast and spindle waves were observed on EEG (10 to 100 μv, 12 to 20 Hz, reference ranges of light sleep 75 to 100 μv, 4 to 6 Hz). The shunt system appeared to be working well, and the findings on MRI were similar to those obtained 8 months after the second operation.

Computed tomography^m of the brain was also performed under general anesthesia and revealed moderate dilatation of the lateral, third, and fourth ventricles; increased thickness of the cerebral parenchyma and brain stem; improvement in the thickness of the cerebellum; a broken drainage tube in the right lateral ventricle; and the tip of the second ventricular drainage tube in the right hippocampus [Figure 5]. The intracranial length of the drainage tube was 29 mm. According to the CT findings, the optimal intracranial length of a drainage tube for a next operation was 15 mm. A third operation to replace the ventricular drainage tube was recommended to the owner, but was declined. The dog was subsequently treated with phenobarbitalⁿ (4 mg/kg PO q 12 hours) for 3 months, and once the seizures were controlled, the phenobarbital was tapered to 2 mg/kg PO q 12 hours.

A third operation was performed 28 months after the second surgery and 3 months after the cluster seizures. During the third operation, the second drainage tube was removed. The radiologically opaque tip of a third ventricular drainage tube was removed to create a hole at its end. An L-shaped connecting tube was inserted into this new drainage tube, and the tube was inserted through the same hole in the parietal bone prepared during the second operation. No abnormalities were noted in CSF removed from the dog at this time. The drainage tube (with an intracranial length of 14 mm) was detected by CT performed immediately after surgery [Figure 6].

The dog had no seizures postoperatively, and phenobarbital was gradually tapered and discontinued 2 weeks after surgery. The dog initially remained in good condition without any seizures or neurological abnormalities. However, the dog died suddenly of severe, tonic-clonic, generalized clustered seizures 3 weeks after the operation. The owner refused a necropsy.

Discussion

Some dogs suffering from syringohydromyelia, with or without hydrocephalus, have been medically managed with glucocorticoids to decrease CSF production and inhibit inflammatory reactions.^2,9,11 Acetazolamide has also been used to decrease CSF production.^2,9,11 However, prednisone was ineffective in the dog reported here, suggesting that medical therapy might not be effective for treating severe cases of syringohydromyelia with hydrocephalus. When medical therapies are ineffective, surgical management must be considered.

Ventriculoperitoneal shunting is helpful in humans with syringohydromyelia in association with hydrocephalus.^1,15,16 Two published reports exist that describe surgical management of hydrocephalus and syringohydromyelia in dogs.^2,3 In one report, ventriculoperitoneal shunting was performed, and in the other, a laminectomy was done. The results of these surgeries were inadequate for both dogs.^2,3 The major reason for failure in the first case was inappropriate placement of the ventricular drainage tube.³ In the second case, incomplete functional recovery of the spinal cord might have occurred because of a lack of drainage of fluid in the syrinx.² In the dog reported here, ventriculoperitoneal shunting was considered, because the dog had similar anatomical abnormalities to humans who improved with ventriculoperitoneal shunting. In this dog, surgery dramatically improved the clinical signs and anatomical abnormalities.

A sectional ventriculoperitoneal shunt was used to facilitate placement of the shunt tip in the lateral ventricle from the parietal bone [Figure 7]. An L-shaped connecting tube was applied into the drainage tube to prevent kinking of the tube, to strengthen it, and to easily modulate its intracranial length. A pump with a safety valve to prevent backflow into the ventricle was used for checking the function of the shunt system. No conclusions could be made as to whether the intracranial tip of the drainage tube should be removed. In retrospect, removal of the shunt tip may have predisposed the shunt to clogging secondary to entry of cellular debris. Manufacturers do not recommend alteration of shunts in this way. More detailed investigations are required to establish the best shape of the drainage tip.

Definitive diagnosis is important in order to define the anatomical abnormalities and understand the pathophysiology of the intracranial and/or spinal cord changes present, as well as to select an optimal surgical procedure. In the dog reported here, MRI was best for delineating the anatomical abnormalities of the brain and spinal cord, and the technique yielded useful information for planning surgery. On the other hand, the ventricular drainage tubes were more clearly observed on CT than MRI. Computed tomography was helpful after surgery to assess the positioning of the drainage tube in the ventricle.

There were three possible mechanisms considered to be responsible for the seizures observed in this dog. One was primary epilepsy, the second was hydrocephalus, and the third was compression of the hippocampus and cerebral cortex by the drainage tube.¹⁷ Based on the clinical course, the findings of MRI and CT, and results of CSF analyses, it was probable that the last mechanism played an important role in the seizures. In retrospect, discontinuation of phenobarbital after the third surgery was probably inappropriate. Because elevations in AST and ALT were observed after the third operation, phenobarbital was tapered and discontinued. Severe generalized seizures resulting in death occurred after the discontinuation of phenobarbital, suggesting that antiepileptic therapy should be continued in animals treated surgically, even when they appear to be normal. The cause of death of this animal was unknown, but it may have resulted from hyperthermia and pulmonary edema associated with protracted, severe seizures.¹⁷

The pathogenesis of the disease observed here was not fully understood. Large and extensive cystic spinal abnormalities in young animals often result from congenital problems.¹ Hence, congenital defects in association with abnormal embryogenesis may have led to the development of hydrocephalus with syringohydromyelia and ventricular cyst in this dog. Hall et al. reported that increased intraventricular pressure of the CSF induces a rise in pressure of the syrinx cavity in the spinal cord, although intraventricular CSF pressure measured during the first operation in the dog reported here was within the reference range.¹⁸ Increased CSF pressure may have contributed to the early development of syringohydromyelia, especially to dilatation of the central canal.^11,19 It was also likely that syringohydromyelia was induced by abnormal CSF dynamics and/or disequilibration of CSF dynamics related to obstruction of the foramen magnum by herniation of the dilated fourth ventricle into the cranial cervical spinal cord.¹ Drainage (decompression) of intraventricular CSF with ventriculoperitoneal shunting dramatically improved not only the clinical signs but also the anatomical abnormalities. The cerebral parenchyma and brain stem also recovered partially after surgery. This improvement suggested that a large volume of CSF in the ventricles and/or syrinx and its related mechanical deformation may play a role in the induction of anatomical abnormalities of the brain and spinal cord in animals with hydrocephalus and syringohydromyelia, even if CSF pressure is normal.

Conclusion

Hydrocephalus, syringohydromyelia, and a ventricular cyst were diagnosed in a 7-month-old, male miniature dachshund with gait abnormalities and altered mentation. Ventriculoperitoneal shunting from a dorsal approach through the parietal bone improved both the clinical signs and the original anatomical abnormalities. Magnetic resonance imaging was helpful for detecting anatomical abnormalities and evaluating postoperative improvements, while CT was more effective for obtaining clear images of the drainage tubes.