Resolution of syringomyelia in ten cases of "up-and-down Chiari malformation" after posterior fossa decompression

Resolução de siringomielia em dez casos de malformação de Chiari observada apenas com o paciente em posição sentada durante a descompressão da fossa posterior

ARTICLE

Resolution of syringomyelia in ten cases of "up-and-down Chiari malformation" after posterior fossa decompression

Resolução de siringomielia em dez casos de malformação de Chiari observada apenas com o paciente em posição sentada durante a descompressão da fossa posterior

José Alberto Gonçalves da Silva^I; Luiz Ricardo Santiago Melo^I; Antônio Fernandes de Araújo^I; Adailton Arcanjo dos Santos Jr^II

^INeurosurgical Division of the Hospital Unimed, João Pessoa PB, Brazil

^IIAssociated Physician

^{Correspondence}

ABSTRACT

The authors describe ten cases of syringomyelia without hindbrain herniation depicted by preoperative magnetic resonance imaging (MRI) in supine position. However, the herniation was observed in all cases during the operation with the patient in sitting position. The postoperative MRI revealed an intense reduction of the syrinx in all patients, as well as it was also observed a clinical amelioration in all cases. The surgical treatment was based on a large craniectomy with the patient in sitting position, tonsillectomy, large opening of the fourth ventricle and duraplasty with creation of a large cisterna magna.

Key words: Chiari malformation, syringomyelia, craniovertebral decompression.

RESUMO

Os autores descrevem 10 casos de siringomielia sem herniação do rombencéfalo, observada na ressonância magnética realizada em decúbito dorsal. Por outro lado, a herniação foi observada em todos os pacientes durante a operação com o paciente em posição sentada. A ressonância magnética pós-operatória evidenciou redução da cavidade siringomiélica nos dez pacientes, bem como foi observada melhora clínica em todos os casos. O tratamento cirúrgico consistiu de craniectomia ampla da fossa posterior, tonsilectomia, abertura ampla do quarto ventrículo e duroplastia com a criação de ampla cisterna magna.

Palavras-chave: malformação de Chiari, siringomielia, descompressão craniovertebral.

The neural dysgenesis, later named as Chiari malformation (CM), was initially described by Cleland¹ and afterwards by Chiari^2,3. Chiari³ reported the anomalies of the hindbrain found in 63 cases of hydrocephalus and he defined the spectrum of anomalies which is now recognized as CM.

In the original description, Type I was characterized by downward displacement of the cerebellar tonsils and the medial portions of the inferior cerebellar lobes which were accompanied by the medulla oblongata into the vertebral canal. The Type II showed downward displacement of the cerebellar tonsils, portions of the inferior vermis, pons, medulla oblongata and, at least, a part of the lengthened fourth ventricle, which reached the disc C4-C5, into the vertebral canal. In Type III, the hydrocephalic cerebellum, pons and medulla were found inside a cervical meningocele (hydroencephaloceles cerebellaris cervicalis), through a spina bifida of the first three cervical vertebrae. In Type IV, there was hypoplasia of the cerebellum without herniation of the cerebellar structures into the vertebral canal.

In this report, the authors present ten cases of syringomyelia (SM) without hindbrain herniation depicted by magnetic ressonace imaging (MRI) in supine position. Nevertheless, this herniation was observed in all patients during the operation in the sitting position. Otherwise, the authors observed an intense reduction of the size of the syrinx, as well as a clinical amelioration in all patients after surgery.

Iskandar et al.⁴ reported on five pediatric cases of SM without hindbrain herniation. All patients improved after undergoing posterior fossa decompression. Kyoshima et al.⁵ described four similar cases with a good recovery of the patients after the decompressive operation. The authors named the impacted cisterna magna by the tonsils of "tight cisterna magna" and designated Iskandar´s et al. description as "Chiari 0 malformation". While these authors did not mention the surgical position of the patients, Iskandar et al.⁴ referred that all patients underwent craniocervical decompression as previously described by Oakes.

METHOD

This study is based on a retrospective review of the patients, five men and five women, with SM without hindbrain herniation. However, this herniation came out during the surgery with the patient in the sitting position (Fig 1). All patients underwent craniocervical decompression previously described by Gonçalves da Silva et al.⁶. This study was approved by the Ethics Committee of Hospital Unimed João Pessoa.

The surgery consisted of a large craniectomy, dissection of the cerebellar tonsils and the regional arteries, large opening of the fourth ventricle, intrapial aspiration of the cerebellar tonsils, suture of the residual pial sacs to the lateral dura mater in ascending position and, finally, a dural grafting was performed with the use of bovine pericardium creating, in this way, a large cisterna magna (Figs 2 and 3).

RESULTS

Ten consecutive patients with syringomyelia and no hindbrain herniation in the supine position were presented. Although, this herniation was observed in all patients during the surgery in the sitting position. All the cases were followed with clinical studies and craniocervical MRI for a mean of 2.8 years and a range of four months to seven years. The age at surgery ranged from 26 to 59 years, with a mean of 35.4 years. All the patients showed significant improvement in symptoms, signs, and syrinx's size in the postoperative follow-up.

The clinical symptoms observed by the preoperative examination are showed in Table 1, the clinical signs in Table 2 and the surgical findings in Table 3.

Six out of the ten cases were associated with basilar impression (BI), as well as four cases were associated with herniation only of the cerebellar tonsils and these were classified as Chiari I malformation. In another six cases were observed partial herniation of the hindbrain structures and were classified as Chiari II malformation. The tonsillar herniation of the ten cases varied from the end of C1 to the beginning of C3. The vascular network anomalies in eight cases were characterized by a left and large posterior inferior cerebellar artery (PICA) in two cases, only a right and large PICA in one case, a large PICA on the right side and one hypoplasic on the left in two cases and, finally, looping sign on the PICAS in three cases.

DISCUSSION

In this report, the authors describe ten cases of SM without hindbrain herniation showed by the MRI in the supine position. However, this herniation was observed in all patients during the surgery in the sitting position. This kind of "up-and-down CM" was observed also in cases without SM^7,8.

Iskandar et al.⁴, on the other side, reported on five pediatric cases of SM without hindbrain herniation; all patients improved after undergoing posterior fossa decompression. The authors hypothesize the rare occurrence of SM resulting from a Chiari-like pathophysiological condition, but lacking a hindbrain herniation.

Newton et al.⁹ described anomalies in the fourth ventricle drainage based on 15 personal adult cases of SM. In 12 out of 14 patients who underwent posterior fossa exploration were found a CM or an occluded foramen of Magendie, or both together. In three cases without a Chiari anomaly there was no foramen of Magendie. Probably that was the first description of the presence of a SM without hindbrain herniation.

Many theories have been presented in attempt to explain the genesis of SM. The development of SM has been observed in relation to congenital or acquired lesions at the foramen magnum or at the spine. Different lesions at the foramen magnum have been commonly reported as CM, BI, membranous occlusion of the foramen of Magendie, arachnoiditis and tight cisterna magna^4,5,10.

Gardner's^11-14 hydrodynamic theory explains the pathogenesis and the development mechanism of communicating central canal cavities, based on foraminal obstruction of the fourth ventricle, which enhanced pulsatile waves in the ventricle (water-hammer-wave) forcing the obex to open and the central canal to expand.

Williams^15-17 proposed the mechanism of the craniospinal pressure dissociation to explain the development of communicating central canal cavities. Cough and sneeze reflexes would increase the intra-abdominal and intrathoracic pressures, increasing the venous pressure and further dilating the epidural venous plexus. This would compress the dural sac, displacing, as a result, the cerebrospinal fluid (CSF), and pushing into the cranial cavity which returns rapidly to the spinal subarachnoid space, as soon as the pressure brought down to the normal levels. In case of tonsillar herniation, the CSF return would be blocked by the cerebellar tonsils which would then work as a valve, occluding the foramen magnum. At this point, the central canal of spinal cord - under a lower pressure than that of the intracranial cavity - would become the ideal place to accommodate CSF. The perpetuation of the phases of craniospinal pressure dissociation causes the formation and maintenance of SM.

Ball and Dayan¹⁸ admitted that CSF penetrates in the central canal of the spinal cord through Virchow-Robin spaces or through the dorsal roots, creating, in this way, the syringomyelic cavity.

The symptomatology appears as the result of the expansion of the syringomyelic cavity and the gliosis affecting the intramedullary and/or the brainstem structures. Milhorat et al.¹⁹ measured the pressure inside the syringomyelic cavity, and suggested that the distention would depend on different degrees of intramedullary pressure, causing lesion of long tracts, gray matter and microcirculation. The involvement of the anterior horn gives rise to fibrillation, fasciculation, muscular weakness and atrophy. However, the compression of the posterior horn and ventral decussation will give origin to syringomyelic dissociation, and, on the other hand, commitment of the sympathetic connection will result in Claude Bernard-Horner syndrome. With the expansion of the cavity, the spinal cord white matter will be compressed, causing a lesion of the pyramidal and extrapyramidal tracts and dorsal columns.

Regarding the surgical technique, all patients of our casuistic of 360 cases of craniovertebral malformations, were operated in the sitting position what facilitates the surgical procedure. Gardner e Goodall¹¹ used this type of position for the operation of 13 out of 17 patients with CM. Later, Gardner¹³ used the same position for the surgical treatment of 74 patients with SM, and on this occasion he introduced the dural graft for the protection of the posterior fossa structures.

The extension of the craniectomy varies in the literature. Because of the small size of the posterior fossa in the presence of BI and/or CM, especially when both anomalies are present, we prefer to use a large craniectomy which extends cranially to the transverse sinus - commonly situated lower than those in normal persons - and laterally to 3-4 cm from the midline. The reason for this large opening is to increase both of the posterior fossa and the cisterna magna, commonly absent in cases of hindbrain herniation, permitting, in this way, the herniated portions of the cerebellum and brainstem to migrate upwards.

Batzdorf ²⁰ and Duddy and Williams²¹ state that the herniation of the cerebellar structures and brainstem, as observed in the postoperative period, are attributed to a large craniectomy. A small craniectomy, on the contrary, might have prevented a decompression from maintained the CSF blockade and perpetuating the craniospinal pressure dissociation. Duddy and Williams²¹, however, using a smaller craniectomy, revealed a frequent downwards migration of the cerebellum and brainstem, and pointed this out as a cause of poor results. These authors observed a downward migration of the posterior fossa structures in 53% of their patients, whereas no change was noticed in 41%, and the ascent of the hindbrain was observed in only one case.

Sahuquillo et al.¹⁰ compared the results obtained in 10 cases in which a small craniectomy was performed, with other 10 patients that underwent an extensive craniectomy. An upward migration of the cerebellum and brainstem was observed in all the last patients, while in those which a small craniectomy was performed there was a downward migration in 7 patients.

The volume of the posterior fossa is notoriously reduced in cases of BI and/or CM, as described firstly by Ackermann²². Milhorat et al.²³ verified a decrease of 13.4 ml in the volume of the posterior fossa and 40% (10.5 ml) in the CSF volume of this region, followed by many authors^24-29.

As to postoperative complications the authors observed pseudomeningocele in 4 cases, from these 2 were reoperated and one associated with hydrocephalus underwent a ventriculoperitoneal shunt. In just one case of pseudomeningocele depicted by postoperative MRI without compression signs of the hindbrain structures, the operation was not indicated.

Iskandar et al.⁴ called attention for idiopathic SM that respond to posterior fossa decompression. The authors hypothesize the rare occurrence of SM resulting from a Chiari-like pathophysiology condition but lacking a hindbrain herniation. We can suggest that the pathophysiology of our cases depend on the "up-and-down CM". As well as, we could suggest that patients with craniovertebral anomalies should undergo a preoperative MRI in orthostatic position to detect hindbrain herniation depending on the body position.

Received 1 January 2010

Received in final form 2 March 2010

Accepted 12 March 2010

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Publication Dates

• Publication in this collection
  20 Oct 2010
• Date of issue
  Oct 2010

History

• Reviewed
  02 Mar 2010
• Received
  01 Jan 2010
• Accepted
  12 Mar 2010