The Dandy-Walker syndrome, hydrocephalus associated with a posterior fossa cyst and dysgenesis of the cerebellum, is relatively uncommon but intriguing in its teratogenic and therapeutic implications. A theory was proposed by Benda, who believed that the syndrome represented maldevelopment in the region of the fourth ventricle but not limited to the foramina. He speculated that failure of normal regressive changes in the posterior medullary velum combined with a congenital absence of the cerebellar vermis results in cyst formation at the caudal end of the fourth ventricle and separation of the cerebellar hemispheres. More recent observations have lent support to this theory. It has been noted in experimental animals, as well as in humans, that certain developmental errors characteristic of the Dandy-Walker syndrome occur before the foramina would normally open and therefore cast doubt on the role of foraminal atresia. Moreover, the occurrence of multiple other anomalies associated with the Dandy-Walker deformity indicates that the pathogenesis is a more basic and complex maldevelopment.
The clinical presentation of the Dandy-Walker syndrome depends to some extent on the combination of developmental anomalies in the infant. If no anomalies other than those affecting cerebrospinal fluid (CSF) circulation are apparent, the presentation is basically one of macrocrania due to intracranial hypertension. The signs of increased pressure, however, may not be severe during the neonatal period and, indeed, in many patients do not become manifest at any time during infancy. Generally, there is fullness of all fontanels and separation of the sutures. The lambdoid suture may be disproportionately widened, and there may be prominent bulging of the occipital bone in relation to the rest of the calvaria. The external occipital protuberance may be abnormally high, but this is not a constant finding. Characteristically, the signs of intracranial hypertension are not accompanied by any external midline defect.
If the developmental anomaly does not become clinically apparent during early infancy, macrocrania may not be the presenting symptom. In older children, cerebellar dysfunction (mainly affecting axial movements rather than the extremities), mental impairment, papilloedema, or extraocular motor deficit, including nystagmus, may be found.
The diagnosis depends on radiologic investigation. Plain roentgenograms of the skull may be helpful but are of limited value. Occasionally, the evidence of macrocranium and suture separation is accompanied by enlargement and prominent deepening of the posterior fossa. In the rare older child who presents for the first time with intracranial hypertension, x-ray films may show elevated portions of the torcular and lateral sinuses.
Presently, brain MRI is the most definitive diagnostic imaging method, demonstrating a rotational axis or compression at the vermis and best delineate any caudal extension of the cyst into the cervical spinal canal or rostral extension through the tentorial incisura. In axial sequences, the cerebellum is usually reduced to two small nodules of neural tissue displaced anterolaterally and not connected by midline tissue. The lateral and third ventricles are usually mildly to moderately enlarged, although this is not uniformly present. If marked enlargement of the lateral ventricles is noted, the possibility of an associated aqueductal stenosis may be considered because the Dandy-Walker deformity alone is usually not accompanied by extreme hydrocephalus.
The differential diagnosis radiologically includes enlargement of the cisterna magna and the presence of an extra-axial arachnoid cyst. Because the mega cisterna magna usually does not occupy nearly the entire posterior fossa, a separate fourth ventricle can be identified along with the presence of a cerebellar vermis. The extra-axial arachnoid cyst may be equally difficult to distinguish, although it is characteristically eccentric and also may be seen to displace a normal fourth ventricle. If there is sufficient doubt regarding the diagnosis, a positive contrast agent may be introduced into the lateral ventricle to determine aqueductal patency, the presence of a fourth ventricle, and any communication with the cystic structure.
The basic triad of the Dandy-Walker syndrome (i.e., hydrocephalus, a posterior fossa cyst, and the absence of the cerebellar vermis) are accompanied by other malformations of the central nervous system (CNS) in about 65 percent of cases. It is thought that these associated anomalies are largely responsible for the prognosis. These include heterotopias of the cerebrum and cerebellum, malformation of the brain stem, polymicrogyria, hamartomas, and agenesis of the corpus callosum. Aqueductal stenosis has been mentioned, and occasional cases of the Dandy-Walker deformity associated with cranium bifidum or spina bifida have also been reported. Systemic anomalies that may accompany the DandyWalker syndrome include cleft palate, syndactyly, polydactyly, and craniofacial deformity. The frequent occurrence of both neurological and systemic anomalies, many of which develop early in embryonic life, before the normal opening of the foramina of Luschka and Magendie, is strong evidence that the syndrome is not simply due to the failure of foraminal opening.
Treatment of the Dandy-Walker syndrome has undergone evolutionary change since the entity was originally recognized, and even today there is no universal agreement regarding its management. Dandy and Blackfan were the first to describe posterior fossa exploration and excision of the cyst membrane. This was the only treatment available for several decades until the advent of ventricular shunting devices. Initially, shunting was performed only if membrane excision did not successfully control the hydrocephalus. Subsequent reviews of several clinical series led to the recognition that the incidence of success from membrane excision was sufficiently small that the primary mode of therapy should be shunting. This has been universally accepted during the past decades, but disagreement still exists as to the optimum position of the proximal end of the shunt. Many authors have advocated using a standard shunt system originating in the lateral ventricle. Raimondi and co-workers have advocated simultaneous Y shunting of the lateral ventricles and the posterior fossa cyst because there is a significant incidence of aqueduct occlusion and because shunting of only the lateral ventricles leads to upward transtentorial herniation from lack of decompression of the cyst. Other observers believe that aqueductal stenosis is rare and can be easily detected by injecting a contrast substance into a lateral ventricle at the time of computed tomography (CT) scanning. On the assumption that communication between the lateral ventricles and the cyst does exist, it is recommended that the proximal end of the shunt be placed within the cyst. This reservoir of CSF, unlike the lateral ventricles, does not collapse on decompression, partially because of the large posterior fossa and the associated cerebellar dysgenesis. Therefore, shunt malfunction due to proximal catheter occlusion is less likely to occur. If communication between the lateral ventricles and the cyst does not exist, an endoscope may be inserted via a lateral ventricle and the membrane responsible for the noncommunication fenestrated to facilitate creation of one compartment. A catheter is directed through the ventricle into the posterior fossa cyst to avoid a complex shunt system.
One can measure the results of treatment of the Dandy-Walker syndrome in terms of mortality, morbidity, or a long-term developmental and functional competence. Mortality ranged between 41-26 percent by several authors. The principal causes of death were shunt infection and cardiorespiratory arrest. The latter complication is a recognized risk in the Dandy-Walker syndrome and has been attributed to the precarious function of a maldeveloped brain stem.
Morbidity associated with ventricular shunting primarily relates to mechanical shunt malfunction and infection. The incidence of each of these entities has decreased in recent years. It is believed that malfunction of the shunt will be reduced further by using the cyst, rather than the ventricles, for shunting.
Several authors reporting, that among the survivors 40-71 percent had subnormal intelligence (IQ <83). The potential inclusion of Dandy-Walker variants into the clinical series may favorably skew the developmental outcome of these individuals. The presence of associated anomalies does not correlate well with lower IQ scores except for the consistently low scores of those patients with agenesis of the corpus callosum. From these observations, one can conclude that the Dandy-Walker syndrome is not limited to a mechanical disturbance of CSF circulation but rather represents a more generalized disorder of neural development.
A young 12 years age patient came to the clinic 30-Jan-2005 for consultation. He had mumps 20 days ago and was admitted to hospital 05-Jan-2005 with clinical picture of lethargy and fever and was treated for meningoencephalitis with CSF WBC 960 and negative CXS results and Latex was also negative. MRI performed 09-Jan-2005 made confusion in the diagnosis, were an arrested Dandy-Walker malformation was seen in its typical triad.
The patient was normal before the mumps attacks with slight enlarged head circumference, without signs of increased ICP. Fundoscopy all the time was normal and neurological examination was normal. The IQ was normal and the parents were advised only to repeat the MRI after 3 months. In case of silent clinical state, it was decided not violate the arrested pathology.
Conclusion: The case was found accidentally by admitting the patient for other causes. There is a golden rule in medicine and in the life in general : don't trigger the silent water. The arrested malformations must be left for follow-up and the policy of wait and see. In case of progressive clinical manifestations , if there is any, then surgical interference must be attempted.