Surgery of Arnold-Chiari Malformation of the I and II Types

S.V. Mozhaev, V.N. Ochkolyas, N.V. Sterlikova

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

There has been a considerable growth of interest in patients with Chiari abnormality of the I and II types after appearance of CT and MRI.

These methods allowed to make suppositions on possible pathogenesis of this disease, to improve existing surgical tactics and ways of surgical treatment. According to Oglezenev K.Ya. et al. (1966), Kanev P.M. et al. (1994), La Marca et al. (1997), etc., surgical intervention is a main method, used in 98% of cases.

Cleland was the first to mention congenital abnormality of craniovertebral localization (1883). In 1891 Chiari divided it into three types with their complete description.

The rate of this disease varies from 3.3 up to 8.2 cases per 1000 men (Blagodatsky et al., 1995).

Pathogenesis of this pathology has not been determined precisely yet. There seem to be three pathogenetic factors: 1. Genetic congenital osteoneuropathies. 2. Traumatic lesions of sphenoid-cribrate and sphenoid-occipital parts of the clivus due to birth trauma. 3. A hydrodynamic blow of liquor at the walls of the central canal of the spinal cord.

Chiari's malformation of the first type (MAC I) is descending of cerebellar tonsils into a vertebral canal below the plane of the great foramen without dislocation of the third ventricle. MAC II is characterized by caudal dislocation of lower segments of vermis cerebelli, medulla oblongata and the third ventricle. MAC III is a rare phenomenon with gross caudal dislocation of all structures of the posterior cranial fossa, accompanied by suboccipital or high cervical encephalomeningocele, which is usually incompatible with life. A typical feature of MAC IV is hypoplasia of the cerebellum without its dislocation in a downward direction (Dandy-Walker type).

A clinical picture of this abnormality is presented by the following syndromes: bulbar, cerebellar, pyramidal, hypertensive-hydrocephalic, syringomyelitic. Hypertensive-hydrocephalic syndrome is the most important of them.

Development and augmentation of hypertensive-hydrocephalic syndrome and focal neurologic symptoms, which are conditioned by cerebellum-stem compression, confirmed by MRI examination, are indications for an operation.

Surgical treatment of MAC I and II assumes use of Gardner's operation and its modifications (with dissection of the dura or arachnoid or without it, resection of cerebellar tonsils, liquor-shunting operations).

Surgical treatment is accompanied by subsiding or complete elimination of headache, partial regression of motor and cerebellum-stem disorders (in 57% of cases).

Patient K., aged 25, was admitted to the Institute on February 4, 2002. He complained of diplopia, ataxic gait, impaired swallowing (choking), gnawing pain in the occipital area. He had been ill during two years. According to the patient's opinion, the disease developed after brain concussion. The last three months were characterized by more marked manifestations and more frequent headache.

Neurologic examination revealed a forced position of a head (protruding forward), minor convergent squint, weak convergence, horizontal diplopia, small-swinging nistagmus at a look in all directions, hyperactivity of deep reflexes with predominance on the right side, ataxia and missing in performance of coordination tests (much worse on the left side), negative Romberg's sign with deflection to the left.

Ophthalmologic examination was indicative of minor myopia and normal visual fields and eye fundus. Craniography showed platybasia with an increase of a basal angle up to 140o. There was a porosity of a posterior margin of the great foramen (Babchin's symptom). MRI examination demonstrated platybasia, basilar impression with dislocation of medulla oblongata in a forward direction and descended cerebellar tonsils, bending of its upper and partially medial segments forward. Pons varolii was flattened; cerebellar tonsils fell into a vertebral canal through the great foramen up to the level of a lower margin of C2; superior vermis was atrophied; cerebellar hemispheres were hypotrophied; the forth ventricle was dislocated a little bit downwards. Cerebral ventricles were characterized by hydrocephalic widening; there was considerable accumulation of liquor in superior and medial segments of the posterior cranial fossa; there was no cisterna magna. As for a subarachnoid space of the spinal cord, a small amount of liquor was visualized at the level of cervical segments. The odontoid process was of a bigger size; it was dislocated backwards to some extent and effected medial segments of medulla oblongata.

A clinical picture of the disease (hypertensive-hydrocephalic syndrome without syringomyelia), dynamics of its development, data of craniography and spondylograpgy, MRI findings allowed to suppose presence of craniovertebral abnormality, i.e. platybasia - basilar impression with Arnold-Chiari malformation of the second type (MAC II). A progradient course of the disease, impaired liquor circulation in the area of Magendie's foramen, compression of a caudal segment of the brain stem and superior spinal roots were indications for operation, aimed at elimination of compression at the level of the craniovertebral articulation and restoration of liquor circulation.

The operation was performed on February 11, 2002. In consisted in resection trephination of the posterior cranial fossa according to Nafziger-Town with resection of the C1 arch and cerebellar tonsils, mobilization of posteroinferior cerebellar and vertebral arteries by means of dissection of arachnoid adhesions between these vessel and meninges.

There were no complications in a postoperative period. The operation resulted in disappearance of headaches, less marked nistagmus and diplopia, as well as equilibrium and coordination disorders.

MRI examination, carried out 4 months later, showed considerable subsiding of internal hydrocephalus and external hydrocephalus in the posterior cranial fossa, free flow of liquor through basal cisterns to anterior segments of a subarachnoid space of the spinal cord.

The demonstration purpose was to present information on a combination of clinical manifestations of craniovertebral dysplasia and MAC II, as well as on a positive result of surgical treatment of this associated pathology.

Female patient Kh., aged 53, was admitted to the Institute on April 22, 2002. She complained of numbness in upper and lower extremities and an abdominal area on the left, periodic weakness in the left hand, pressing headache, ataxic gait, dizziness attacks, dysuria. The patient had been ill during 10 years. The disease onset was characterized by dizziness and feeling of heat, ataxic gait. Treatment of cervical osteochondrosis (diagnosis made by a neuropathologist) was ineffective. The past medical history contained information on craniocerebral trauma (an occipital area), sustained at the age of 23.

The first episodes of numbness and weakness in the left extremities, especially in the third, forth and fifth fingers of the left hand, were experienced in October 2001. In March there was an episode of dysuria. She suffered from periodic pressing headache in an occipital area, which irradiated along the neck back and shoulders. Sometimes it was accompanied by nausea.

MRI examination (21.04.02) was indicative of an upper retrocerebellar cyst (4.5x2.5 cm), falling of cerebellar tonsils into the great foramen up to the superior margin of C2 and formation of a new pathway of liquor outflow through a rupture in posterior segments of the third ventricle, tentorium notch and subarachnoid areas of the posterior cranial fossa; dislocation of superior segments of medulla oblongata and pons varolii in a forward direction; occlusion of the aqueduct.

Neurologic findings were as follows: elements of dysraphia (high hard palate, a keel-like breast bone); oculomotor disorders, manifesting themselves in convergent squint, incomplete volume of eyeball movements to an external side, weak convergence on the right; diminished pharyngeal reflex; low muscular tonicity; left-sided pyramidal deficiency; intention tremor on both sides in performing coordination tests; negative Romberg's sign; minor pelvic disorders of a dysuria type.

Cranio- and spondylography revealed hypertensive-hydrocephalic changes on bones of the skull fornix and base, minor hypoplasia of C1, diffuse dystrophic changes in the cervical spine with osteophytes of C5, C6 bodies.

According to PET data, there was Arnold-Chiari abnormality with falling of cerebellar tonsils into a vertebral canal to a distance of 13 mm and initial signs of blood flow congestion in protruding areas of tonsils.

Hypertensive-hydrocephalic syndrome was predominant in a clinical picture of the disease. One could watch elements of spinal syndrome (left-sided temperature hypesthesia, minor pelvic disorders) and cerebellar deficiency with moderate disorders of static and dynamic coordination, which were probably conditioned by craniocerebral trauma, sustained earlier.

Clinical diagnosis was as follows: MAC I, partial occlusion of liquor pathways at the level of the posterior cranial fossa, internal and external communicating hydrocephalus.

The disease was characterized by a progradient course with augmenting hypertensive-hydrocephalic syndrome, caused by falling of the cerebellar tonsils; syndrome of cerebellar deficiency; elements of spinal syndrome. This pathology was an indication for surgical intervention.

The patient was operated on April 22, 2002. Trephination of the posterior cranial fossa and resection of cerebellar tonsils were performed. The operation revealed gliosis of tonsils, which fell up to an upper margin of C2. They were gray-cyanotic and had a lot of vessels on their surface. Besides, a cicatricial-adhesive process was watched. Resection of tonsils resulted in free flow of liquor into the operative wound. The dura defect was closed by a fragment of aponeurosis.

A postoperative period was uncomplicated. There was regression of intracranial hypertension and pelvic disorders; disturbances of static and dynamic coordination became less marked. However, oculomotor disorders (weak convergence on the right), temperature hypesthesia on the left, subjective sensation of numbness in the left extremities were still persistent on discharge.

According to MRI examination, carried out in 5 months, a flow of liquor in subarachnoid spaces of the spinal cord was normal; medulla oblongata and upper segments of the spinal cord returned to their normal position; internal hydrocephalus decreased.

The demonstration purpose was to show a combination of clinical manifestations of disontogenetic pathology and posttraumatic sequelae in the form of hypertensice-hydrocephalic syndrome, whose course was complicated by falling of cerebellar tonsils with aggravation of liquor circulation disorders at the level of the craniovertebral articulation.

Female patient Sh., aged 34, was admitted to the Institute on May 21, 2002. She complained of permanent numbness and violent gnawing pain in both arms, an upper half of the thorax and the neck back, painless burning in this area, periodic headache and impaired swallowing (choking). The first signs of the disease developed about 6 years ago. At the beginning the patient experienced sensation of cold in her right arm; later there appeared numbness. She was treated for cervical osteochondrosis by a neuropathologist without any marked effect. Painless burning in the arms and an upper half of the thorax appeared three years ago.

The patient was admitted to the Clinic of Neurology of the Saint Petersburg State Medical University in September 2000. MRI examination of the cervical and thoracic spine showed a cyst of the spinal cord canal at the level of C2-Th5. Syringomyelia was diagnosed and radiation therapy was carried out. However, there was no improvement. The patient started to choke in swallowing; her voice became hoarse; there appeared pressing pain in the occipital area.

In April 2002 she was admitted to the Clinic of Neurology of the Mechnikov Medical Academy. MRI examination of the brain revealed Arnold-Chiari malformation. Surgical treatment was recommended.

Neurologic findings were as follows: dysraphia (osteofacial asymmetry, a high hard palate); horizontal nistagmus with a rotatory component at a look to the sides (especially to the right); a smoothed down nasolabial fold; a dissociated disorder of sensation in Zelder's facial zones; choking in swallowing; paresis of the left arm (up to the score of 4); hypotrophy of muscles of the left hand; asymmetric deep reflexes (D>S); dissociated disorders of sensation of a "jacket" type; reduced muscular tonicity. The patient performed coordination tests with a lack of confidence and intention tremor. Romberg's sign was negative.

Cranio- and spondylography of the cervical spine were indicative of craniovertebral dysplasia (Kimmerly's syndrome, hypoplasia of C1 mass, the first degree of C1 concrescence).

MRI examination showed dislocation of medulla oblongata in a forward direction with its excavation on a dorsal surface. Cerebellar tonsils fell into a vertebral canal up to 12.9 mm. The great cistern was narrowed to a considerable extent. There was narrowing of an anterior subarachnoid space, though it was patent; its posterior segment was narrowed very much. Cysts of central and paracentral localization, communicating with each other, were watched in cervical (beginning with C2), upper and middle thoracic segments of the spinal cord.

PET examination of the brain with 15O-water radioactive substance demonstrated asymmetric prolapse of both tonsils into a vertebral canal to a distance of 15 mm. Blood flow was reduced by 31% in a protruding part of tonsils (mainly of the right one).

The following diagnosis was made: Arnold-Chiari abnormality of the first type, syringomyelia of a cervicothoracic form.

Indications for an operation were as follows: a progradient course of the disease; syringomyelia, lesion of the brain stem, a caudal group of cranial nerves and upper cervical roots, conditioned by dislocation of cerebellar tonsils and causing liquor circulation disorders.

The operation, made on May 29, 2002, consisted in trephination of the posterior cranial fossa, C1 resection, partial resection of a spinous process of C2, resection of cerebellar tonsils, dissection of arachnoid adhesions. The right tonsil was bigger and fell lower, than the left one.

A postoperative period was characterized by absence of any complications. Headache and pain in the neck, back and shoulders disappeared; coordination disorders and manifestations of paresis of the left arm reduced considerably; there were no nistagmus, choking, sensational disorders in a facial area. The patient was discharged.

MRI examination, carried out 2 months later, showed, that a syringomyelitic cyst of the spinal cord had almost disappeared and suboccipital spaces had widened.

The demonstration purpose was to give information on a course of MAC I with formation of syringomyelitic cysts and a good result of surgical treatment.