Syringomyelia, Noncommunicating Isolated

Description

Syringomyelia (Greek: 'syrinx,' pipe, and 'myelos,' marrow) is a tubular cavity in the spinal cord. It can occur sporadically in association with spinal cord tumors, inflammatory arachnoiditis, or posttraumatically. It is rarely idiopathic (less than 1% of cases). The vast majority of cases of syringomyelia are cervical, noncommunicating, and associated with an abnormality at the foramen magnum, particularly the Chiari malformation type I (CM1; 118420), as well as basilar impression (109500) and Dandy-Walker malformation (220200) (Speer et al., 2003; Levine, 2004); these cases have shown familial segregation.

The form of syringomyelia discussed here is 'noncommunicating' with the fourth ventricle, but may communicate with the subarachnoid space. In contrast, 'communicating' syringomyelia, or 'hydromelia,' opens rostrally into the fourth ventricle and almost always occurs in children with hydrocephalus, Chiari malformation type II (CM2; 207950), and spina bifida (see 182940) (Levine, 2004).

Clinical Features

Caraceni and Giovannini (1977) reported 4 sibs with syringomyelia who had symptom onset in their thirties or forties. Each had variable clinical features, including segmental loss of pain and temperature sensation, muscle weakness and atrophy of the upper limbs and hands, nystagmus, urinary incontinence, and lower limb hyperreflexia and spasticity. Radiographic studies of some of the patients showed an enlarged foramen magnum and spinal canal.

Busis and Hochberg (1985) reported 2 sisters with syringomyelia. One sister reported loss of pain and temperature sensation in the left arm, shoulder, and face since age 12 years. She also had right Horner syndrome, rotary nystagmus, and absent left gag reflex. Radiographic studies showed low-lying cerebellar tonsils and cervical syringomyelia. Her sister, mother, and brother had similar symptoms, but radiographic examinations were not performed. The authors recognized that syringomyelia is often associated with Chiari type I malformation and basilar impression, but suggested that this family lacked definite anomalies of the craniocervical junction. Autosomal dominant inheritance was suggested.

Zakeri et al. (1995) stated that 16 families with syringomyelia had been reported since 1899 and noted several early references (Redlich, 1916; Barre and Reys, 1924; van Bogaert, 1929). In an accompanying commentary, Hoffman (1995) suggested that all familial cases of syringomyelia have a primary defect in the region of the foramen magnum resulting in Chiari malformation type I or basilar invagination. Syringomyelia results secondarily from disordered cerebrospinal fluid (CSF) dynamics occurring in this area. Accordingly, some affected members of a family may have isolated basilar skull defects whereas others go on to develop syringomyelia.

Pathogenesis

Gardner (1965) proposed a hydrodynamic mechanism to explain the development of communicating syringomyelia based on abnormal delayed opening of the roof of the fourth ventricle, persistence of the connection between the fourth ventricle and the spinal canal, and high CSF pressure pulsations exerted by the choroid plexus. The exaggerated pulsations would be directed into the central canal, resulting in hydromelia. The central canal could also rupture at various other points, resulting in syringomyelia (Levine, 2004).

Williams (1969) postulated that obstruction of the subarachnoid space at the level of the foramen magnum could act as a valve allowing CSF to flow rostrally more effectively than caudally, resulting in a craniospinal pressure dissociation and formation of a cavity.

In a postmortem analysis of 105 patients with syringomyelia, Milhorat et al. (1995) concluded that there are 3 distinct types. The first type (47 cases) encompassed dilations of the central canal that communicated directly with the fourth ventricle ('hydromelic') and were associated with hydrocephalus and severe birth defects, such as Chiari type II malformation and open spina bifida. The second type (23 cases) consisted of noncommunicating central canal syrinxes ('syringomyelic') that arose at variable distances below the fourth ventricle and were associated with disorders that affect CSF fluid dynamics, such as Chiari type I malformation and basilar impression. The third group (35 cases) included extracanalicular parenchymal syrinxes that did not communicate with the central canal and were associated with injurious spinal cord lesions, such as trauma, infarction, or hemorrhage. The findings established several forms of spinal cord syrinxes with different etiologies and pathogenesis.

Levine (2004) proposed a novel theory of the pathogenesis of syringomyelia associated with lesions at the foramen magnum. Obstruction of the subarachnoid space at the foramen magnum leads to transient abrupt changes of CSF pressure with increased pressure rostral to the block and decreased pressure caudal to the block. These changes produce corresponding changes in transmural venous pressure, causing compression of vessels above the site of compression at the foramen magnum and dilation of vessels below. This leads to mechanical stress on the spinal cord resulting in tissue breakdown and partial disruption of the blood-spinal cord barrier, allowing a plasma infiltrate to accumulate in the spinal cord forming a syrinx.

Animal Model

Ostertag (1930) found dominant inheritance of syringomyelia in rabbits.