Pathogenetic Aspects and Surgical Treatment of Chiariís Anomaly of the First Type

S.V. Mozhaev, N.V. Sterlikova

(Institute of Human Brain of the Russian Academy of Sciences, Saint Petersburg)

Chiariís anomaly of the first type is still an urgent problem of neurosurgery. The rate of this pathology has grown since the appearance of up-to-date methods of neuroimaging. However, the most effective tactics of treatment and precise indications for surgical intervention have not been elaborated. Some aspects of the anomaly pathogenesis and its complications, in particular syringomyelia development, are unclear.

There were 92 adult cases with Chiariís anomaly, treated at the Institute of Human Brain during 1997-2006; 28 of them had syringomyelia.

The analysis of clinical and neurological symptoms revealed hypertensive-hydrocephalic syndrome (66.3%), bulbar-pyramidal syndrome (60.9%), cerebellar syndrome (79.3%), radicular syndrome (89.1%), syringomyelic syndrome (28.3%) and syndrome of vertebrobasilar insufficiency (53.3%).

The data of MR-examination served the basis for determining two anatomic-and- clinical versions of Chiariís anomaly of the first type, dependent on a predominant type of stem structures compression. Compression of a dorsal surface of medulla oblongata by cerebellar tonsils was considered to be a posterior version of this anomaly, diagnosed in 47 cases (51.1%). Compression of a ventral surface of the stem by structures of the so-called denticlival complex, usually watched in accompanying abnormalities of the skull base and upper cervical spine, and simultaneous compression of a dorsal surface by cerebellar tonsils are characteristic of an anteroposterior version of the above anomaly. It was revealed in 45 cases (48.9%).

Surgical interventions were performed in 32 cases. The rest 60 patients were treated conservatively. Progradient forms of Chiariís anomaly of the first type with aggravation of clinical and neurological symptoms and such complications, as syringomyelia and progressing hydrocephalus were indications for an operation.

Methods of surgical treatment included resection trephination of the posterior cranial fossa; opening of the dura and arachnoid; division of cicatricial adhesions between meninges, vessels and nerves; subpial resection of cerebellar tonsils (60-70%); reconstruction of the great occipital cistern by means of dura plasty; creation of layer-by-layer aponeurotic-muscular support. Osteoplasty of a trephination defect with autobone chips was performed in 13 cases.

The analysis of clinical and neurological symptoms, carried out after treatment, demonstrated, that surgery had allowed to eliminate hypertensive-hydrocephalic syndrome, to achieve marked reduction of bulbar-pyramidal, cerebellar, radicular and vertebrobasilar insufficiency syndromes in the nearest postoperative period. Besides, all operated cases were characterized by improvement of a state according to Karnovsky scale and better adaptation to working activity. Patients, receiving conservative therapy, did not show marked reduction of clinical and neurological signs. On the contrary, some of them had augmentation of symptoms and reduced adaptation to social and working activity.

Data of postoperative MR-examination were indicative of a smaller size of syringomyelic cysts in 76.9% of cases. Disappearance of these cysts with regression of focal symptoms was spontaneous and took place after restoration of physiologic liquor circulation at a craniovertebral level. It was due to filling of a spinal subarachnoid space with liquor and subsequent expelling of congested liquor from cysts via the central canal opening.

Thus, the study allows to state, that surgical intervention, performed on the basis of the above information, is the main method of treatment in Chiariís anomaly of the first type.