Spontaneous resolution of syringomyelia in Chiari I malformation: A review of literature
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/neuroindia.NI_899_16
Source of Support: None, Conflict of Interest: None
Syringomyelia is defined as a "tubular cavitation" within the spinal cord. The exact etiology is not known although a craniovertebral anomaly such as an atlantoaxial dislocation, basilar invagination and/or Chiari I malformation form the most common etiology. The natural history of syringomyelia is highly unpredictable with some patients experiencing a spontaneous improvement in the neurological status as well as a resolution in the syringomyelia without surgery. However, the mechanisms responsible for the formation and spontaneous resolution of syringomyelia in patients with associated Chiari I malformation remain controversial. Less than 10 cases of spontaneous resolution of the syrinx have been reported in the literature [Table 1].
A 32-year old lady presented with a history of neck pain and paresthesia in both upper limbs 30 months prior to her presentation in our hospital. Neurological examination revealed a normal motor power, the dissociation of sensations below the C4 dermatome, the diminution of biceps reflex bilaterally, and the presence of brisk deep tendon reflexes in other regions. Magnetic resonance imaging (MRI) of the craniovertebral junction and spine showed descent of the cerebellar tonsils into the cervical canal up to 9 mm; and, a syrinx was noted at the cervical and dorsal levels [Figure 1]. There was also evidence of a small disc-osteophyte complex at the C5-6 level on the left side with no significant cord compression. The patients was advised to undergo a foramen magnum decompression. As she was not willing to undergo surgery, she was discharged. After an interval of 30 months, the patient presented with severe neck pain of a month's duration with left-sided brachialgia. Clinical examination revealed a normal power, with decreased sensation in the left C5-6 dermatome. Deep tendon reflexes were brisk in both upper and lower limbs. A repeat MRI showed resolution of the syrinx at the cervical and dorsal levels despite persistence of crowding of the posterior fossa structures at the level of the foramen magnum [Figure 2]. The paracentral disc-osteophyte complex at the C5-6 level had progressed, leading to significant cord and neural foraminal compression on the left side.
As the patient's symptoms, such as paresthesia of all the four limbs that were thought to be due to the presence of Chiari I malformation had reduced, and the repeat imaging had suggested spontaneous resolution of her syrinx, her current symptoms were attributed to the increase in the C5-6 disc prolapse. Hence, she underwent a C5-6 anterior cervical microdiscectomy. Postoperatively, the patient had complete relief in her symptoms.
Syringomyelia is a manifestation of different pathologic processes. Syringomyelia may be congenital or developmental. Its natural history is variable and poorly understood. Syringomyelia has different classifications. Milhorat  classified syringomyelia into three types: (a) a communicating syrinx, occurring with hydrocephalus and anatomically continuous with the fourth ventricle; (b) a non-communicating syrinx, separated from the fourth ventricle by a syrinx-free segment of the spinal cord and occurring with Chiari malformation More Details, extramedullary compressive lesions, spinal cord trauma, intramedullary tumors or infections; and, (c) an atrophic syrinx, occurring with myelomalacia. Batzdorf  classified syringomyelia into: (a) syringomyelia related to anomalies at the craniovertebral junction; and, (b) syringomyelia related to abnormalities at the spinal level. In a majority of patients, syringomyelia is due to Chiari I malformation. Chiari II malformation may be associated with myelomeningoceles at the cervical or thoracic level.
The exact mechanism of cyst formation in syringomyelia is unknown. Chiari  believed that the fluid was present in the cord due to the persistence of an embryonal state (hydromyelia) associated with hydrocephalus; the syrinx in his model would be of the communicating variety. Gardner  proposed the hydrodynamic theory to explain the association of hydrosyringomyelia with Chiari malformation. In the presence of Chiari malformation, the caudally displaced tonsils obstruct the foramen of Magendie and continue to direct the pulse wave into the central canal. Williams  proposed a modification of the hydrodynamic theory, in which venous pressure changes were responsible for the formation of hydrosyringomyelia. During coughing or Valsalva maneuver, venous engorgement of epidural veins forces cerebrospinal fluid (CSF) into the spine rostrally. The herniated contents of the posterior fossa then act as a ball valve to trap the fluid intracranially. After the intracranial pressure dissipates, there is a craniospinal pressure dissociation that tends to suck the cerebrospinal fluid caudally through the patent central canal.
Pinna et al., conducted CSF flow dynamic studies for understanding the pathogenesis of syrinx formation. The aim of the study was to investigate whether or not differences in CSF flow dynamics in patients with Chiari I malformation could account for the different clinical and radiological presentations. The findings of the study supported the hypothesis that, in Chiari I malformation, an elongated systolic flow may prolong the condition of increased spinal subarachnoid pressure caused by the foramen magnum obstruction, thus favoring CSF penetration into the spinal cord. A shortened systolic flow, on the other hand, may be insufficient to maintain a hypertensive condition for enough time to induce syrinx formation.
Clinically, majority of patients presenting with a syringomyelia associated with Chiari I manifest their symptoms in young adulthood. There is a slow progression of the disease and the course may extend over many years. The onset may be acute if the syrinx is at the brainstem level. Clinically, the signs and symptoms depend on the location of the syrinx. Majority of the patients with syringomyelia present with occipital headache, neck pain, dissociated sensory loss due to spinothalamic fiber damage, and spastic paraparesis (upper motor neuron weakness in lower limbs and lower motor neuron weakness in upper limbs). The sensory deficit representative of an intramedullary pathology includes a "cape like" or suspended sensory loss. The posterior columns may also be involved by a large syrinx. Due to the anterior horn cell involvement, wasting of the upper limb extremities may also occur. Bladder disturbances usually occur late. Horner's syndrome can occur due to the involvement of the intermediolateral cell column of the spinal cord that relays the sympathetic fibres.
Magnetic resonance maging (MRI) is the investigation of choice. The level of the syrinx and associated soft tissues abnormalities at the craniovertebral junction are well demonstrated. Recently, a cine-mode T2-weighted MRI has been proposed to study the CSF flow. Plain radiographs can detect the bony abnormalities.
The natural history of syringomyelia varies. No large study is available. The clinical presentation may vary through the entire range from a complete regression of symptoms to the development of progressive neurological deficits. An operative management is considered if there is progressive worsening of symptoms and enlargement of syrinx. The various modalities of treatment include a ventriculoperitoneal shunt (in the presence of associated hydrocephalus), foramen magnum decompression, duroplasty, and syringosubarachnoid shunting. Very few cases of spontaneous resolution of syrinx have been reported in the literature. The mechanism of spontaneous regression is not known. Perrini  reported a case of resolution of syringomyelia that occurred despite the presence of a tight cistern magna. He reported that the cessation of daily physical strain could affect the natural history of syringomyelia. Klekamp et al., reported a case with complete regression of symptoms and spontaneous resolution of the syrinx after 32 months. Regression was attributed to the spontaneous recanalization of CSF pathways at the foramen magnum, which most likely was due to rupture of the arachnoid membranes that had obstructed CSF flow. Kyoshima et al., reported two cases of spontaneous resolution of the syringomyelia and attributed it to the spontaneous correction of the abnormal cerebrospinal fluid flow, or the drainage of the syringomyelic cavity into the spinal subarachnoid space due to the occurrence of spinal cord fissuring. Coloma  reported the case of a 2-year old male child with Chiari malformation in whom there was complete disappearance of the syrinx after 36 months. Itoyama et al., reported a case of syringomyelia with spontaneous regression of symptoms in a month's time with radiological evidence of shrinkage of the syrinx. Mazumder et al., have also reported the spontaneous resolution of both Chiari malformation and associated syringomyelia in a 5-year old girl following stabilization of her seizure episode. They speculated that raised intracranial pressure during the seizure episode might have predisposed to the syringomyelia. In the subsequent seizure-free period, intracranial and intraspinal pressures might have stabilized leading to resolution not only of syringomyelia but also of Chiari I malformation.
In our case, the resolution of the syrinx was noted after an interval of 30 months. Our case is unique because not only was there was resolution of syrinx but the patient also presented with another pathology with severe neck pain and left upper limb radiation. The MRI imaging revealed resolution of syrinx; however, the patient was symptomatic due to the C5-6 disc prolapse. She had complete relief of neck pain after an anterior cervical microdiscetomy; she also did not manifest any symptoms related to Chiari malformation and syringomyelia, following the resolution of her syringomyelia.
Spontaneous resolution of syringomyelia associated with Chiari I malformation is exceptionally rare with less than 10 cases reported in the literature. The exact mechanism for spontaneous resolution of the syrinx is not known. The interval of resolution of syrinx varies from 1 month to 60 months in different case reports. The mean interval within these limited cases has been approximately 24 months. As the natural history of syringomyelia has been so variable, a larger number of case studies are required to predict the cause of spontaneous regression of the syrinx.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
[Figure 1], [Figure 2]