Intramedullary tumors associated with syringomyelia always display contrast enhancement on MRI. The most common entities are ependymomas (Fig. 9.1) and angioblastomas (Fig. 9.2). Whereas ependymomas associated with syringomyelia are solid space-occupying tumors, which are easily detected on MRI after application of gadolinium (Fig. 9.1), the diagnosis of an angioblastoma may not be straightforward. They tend to be localized in the dorsal root entry zone of the cord and may be quite small [24] (Fig. 9.2).

If tethered cord syndromes cause syringomyelia, these syrinx cavities tend to be rather small and of no clinical significance (Fig. 9.3). A large syrinx of the entire cord is rarely observed in patients with a tethered cord syndrome. The diagnostic challenge in these patients is the identification of all tethering elements, which tend to be localized below the lower pole of the syrinx. Such elements, which can be found in various combinations in a particular patient, are a thickened filum terminale, a split cord malformation (Fig. 9.3), or a lipoma fixed at the dura to mention the most frequent [19].

In patients with Chiari malformations, CSF flow can be compromised by cerebellar tonsils filling the space of the cisterna magna, by arachnoid scarring in the foramen magnum area, and by obstruction of the foramen of Magendie (Fig. 9.4). Whereas the obstruction by cerebellar tonsils is clearly apparent on a preoperative MRI, arachnoid adhesions and an obstruction of the foramen of Magendie are mostly intraoperative findings and need special attention during surgery [18].

In posttraumatic syringomyelia, CSF flow obstruction may be caused by arachnoid scarring at the trauma level as well as narrowing of the spinal canal due to posttraumatic stenosis or kyphosis (Fig. 9.5). Furthermore, posttraumatic cord tethering may contribute to syrinx development. Depending on associated injuries to vertebral bodies and joints, MRI may not be sufficient for surgical planning. CT scans in bone window technique may be very helpful to localize and determine bony landmarks for intraoperative orientation as well as the position of implants in patients who require a spondylodesis [21].

In the absence of a craniocervical malformation, an intramedullary tumor, or a history of spinal trauma, syringomyelia is still considered idiopathic by many physicians. However, these patients have to be evaluated very carefully for radiological and clinical signs of arachnoid pathologies in the spinal canal causing CSF flow obstructions [22] (Fig. 9.6). The syrinx starts at the level of obstruction and expands from there. If the syrinx expands in rostral direction, the obstruction will be found at the caudal end of the syrinx and vice versa. This also implies that the obstruction will most likely be found close to the largest diameter of the syrinx [22] (Fig. 9.6).

Due to the pulsatile movements of arachnoid septations, webs, or cysts, standard MRIs may not always be able to demonstrate an arachnopathy directly. With a history of spinal meningitis or subarachnoid hemorrhage [5], the often quite extensive arachnopathy is rather easy to diagnose by MRI (Fig. 9.7). Many arachnopathies, however, are quite discrete and extend over a few millimeters only (Fig. 9.6). Cardiac-gated cine MRI should be employed for such instances to study spinal CSF flow to identify areas of flow obstruction which may correspond to such circumscribed arachnoid pathologies [1, 22]. Sometimes significant flow signals can also be detected in the syrinx itself. In such cases, the highest flow velocities in the syrinx can be expected adjacent to the arachnoid scarring. The spinal cord should be studied with thin axial slices in T2-weighted images over the entire extent of the syrinx to search for areas of cord compression, displacement, or adhesion to the dura [7, 14, 22]. In the sagittal plane, the contour of the cord may appear distorted in areas of arachnoid scarring (Fig. 9.6). CISS (constructive interference in steady state) sequences can be used not only for the demonstration of the syrinx [12] but may also be helpful to detect arachnoid webs, scars, and cysts, because this technique is less susceptible to CSF flow artifacts [12]. Myelography and postmyelographic computer tomography (CT) are alternative methods to demonstrate arachnoid pathologies but have a lower sensitivity [22].

The sequence of events leading to a syrinx has implications not only for the neuroradiological appearance as just described but also for the evolution of clinical symptoms. The syrinx develops as a consequence of a series of events that originate from a pathology leading to CSF flow obstruction. For almost all entities leading to syrinx development, this process requires many years. Therefore, the first neurological symptoms in the patient’s history are commonly caused by this underlying pathology rather than the syrinx. In other words, a carefully taken clinical history can provide clues to the underlying pathology. If neurological signs spread to other parts of the body in an ascending pattern, the cause of the syrinx will be located at the lower pole of the syrinx and vice versa similar to the radiological evolution of the syrinx. Apart from trauma, arachnoid scarring may be related to infection [16] (Fig. 9.7), hemorrhage [5], irritation by outdated contrast agents such as pantopaque [28], or surgery, to mention a few [22].

It is always puzzling that patients may harbor a huge syrinx and yet have just minor symptoms with exactly the opposite observation for some smaller syrinx cavities associated with major neurological deficits. One explanation for this paradox may be that a great deal of the clinical problems are related to the underlying disease process causing the syrinx rather than to the syrinx itself [25]. This is particularly evident for syringomyelia associated with intramedullary tumors or cord tethering.

The classical symptom of syringomyelia is a dissociated sensory loss with loss of sensation for temperature and pain but preserved sensation for light touch. Pain related to syringomyelia is either permanent or aggravated by maneuvers such as coughing and sneezing and perceived in dermatomes corresponding to the level and extension of the syrinx. Syrinx pain represents neuropathic pain. In order to produce neuropathic pain, a syrinx must have reached the region of the dorsal horns close to the dorsal root entry zone. Quite commonly, patients report that their pain was associated with coughing or sneezing initially before becoming permanent. Other types of pain which patients report quite often, such as pain associated with exertion, cannot be explained by syringomyelia and are caused by other mechanisms such as muscular spanning to mention a common example. Late symptoms of syringomyelia are muscle atrophies corresponding to damage of ventral horn cells or trophic changes leading to skin and joint damages, particularly in the shoulder and elbow [25].

Successful treatment of syringomyelia requires to treat the underlying cause – preferably before significant neurological deficits have developed. For syringomyelia associated with intramedullary tumors and Chiari I malformation, the rates for postoperative syrinx resolution are above 80 %, provided the tumor is removed and all components contributing to CSF flow obstruction in Chiari malformations have been surgically addressed, respectively [18, 20]. Syrinx cavities related to tethered cord syndromes tend to be of small caliber and extension. Therefore, complete untethering caused a postoperative reduction in just 13 %, whereas the syrinx remained unchanged in 87 % [19].

Successful treatment of syringomyelia related to spinal rather than craniocervical CSF flow obstructions is much more challenging. The underlying causes are more difficult to identify and to deal with surgically. For this reason, surgery on spinal arachnopathies for treatment of syringomyelia should be reserved for patients with progressive symptoms. Nevertheless, treating the cause of the syrinx with arachnolysis, untethering the cord, and duraplasty is rewarded by considerably better results compared to syrinx shunting procedures [21–23, 25, 33, 37].

Neuropathic pain and dysesthesias, particularly those of burning character, may be major clinical problems. Even though these may improve to some degree with successful treatment of the syrinx, this is never certain. Therefore, the decision for or against surgery should be based on the course of neurological signs and symptoms rather than pain syndromes alone [22].

In general, surgery can be recommended for patients with arachnoid scarring limited to about 2–3 spinal segments [22] (Fig. 9.5). All operations are performed in prone position. Laminotomies are recommended to reinsert the lamina at the end of the operation with titanium miniplates. After exposure of the dura, the extent of the arachnoid pathology and the syrinx can be visualized with ultrasound. Pulsations of syrinx fluid and CSF may become visible. Most importantly, the safest spot for opening of the dura can be chosen with this technique. As contamination of the CSF with blood may cause inflammatory reactions of the arachnoid, great care must be taken to achieve good hemostasis. For this purpose, the entire surgical field is covered by moist cottonoids, which keep soft tissues moist and soak up any minor bleeding. Then the dura is opened under the operating microscope in the midline without opening of the arachnoid. Once the dura is held open with sutures, the arachnoid pathology can be studied, and adequate exposure cranially and caudally is ensured in order to gain access to a normal and unaffected subarachnoid space on either end (Fig. 9.8a). Obviously, any surgeon should be familiar with the normal anatomy of the spinal subarachnoid space [34]. The posterior subarachnoid space is divided in two halves by a posterior longitudinal arachnoid septum. This septum extends between the outer arachnoid layer and an intermediate layer on the cord surface. The insertion on the cord surface is related to the midline dorsal vein. Further strands of arachnoid may be encountered in the posterior and lateral subarachnoid space. These arachnoid webs and septations are a physiological feature of the thoracic spinal canal. In the cervical area, the posterior longitudinal septum may be absent, and lateral arachnoid webs between nerve roots, which are considered to promote CSF flow in the thoracic spine, are not present. Under normal conditions, no arachnoid webs or septations exist in the entire anterior spinal subarachnoid space. A good landmark for dissection are the dentate ligaments, which originate from the spinal cord pia mater, run between posterior and anterior nerve roots, and insert close to the dural nerve root sleeve. With a microdissector, arachnoid and dura can be separated from each other without any problem in areas without arachnoid scarring, i.e., at either end of the exposure. In the area of scarring, sharp dissection with microscissors is usually required to achieve this (Figs. 9.8b, c). At the level of CSF flow obstruction, the arachnoid may become densely adherent to the cord surface. With opening of the rostral and caudal subarachnoid space, CSF flushes into the surgical field, and often the cord, which was distended by the syrinx, starts to pulsate, and the syrinx may collapse at this point. The arachnoid scar can be resected layer by layer leaving a last sheath on the cord surface to avoid injury to the cord or surface vessels (Figs. 9.8d, e). This last layer resembles the intermediate arachnoidal layer mentioned above. In this way, a free CSF passage in the posterior subarachnoid space can be created in every patient across the region of the arachnopathy. Dissection is then continued laterally on either side toward the dentate ligaments. This leads to a complete untethering of the cord in the majority of cases. No arachnoid dissection should be performed anteriorly of the dentate ligaments to avoid injuries to motor pathways and anterior spinal cord vessels. Closing the microsurgical part of the operation, an expansile duraplasty is inserted with a tight running suture and finally lifted up with tenting sutures on either side (Fig. 9.8f). To avoid scar formation and tethering between duraplasty and the spinal cord, alloplastic material for duraplasty should be preferred, i.e., Gore-Tex® (W.L. Gore & Associates GmbH, 85640 Putzbrunn, Germany). Special attention is finally paid to a good, tight closure of the muscle layer to prevent any CSF from entering the epifascial space. In patients who have been operated before, as in patients with posttraumatic syringomyelia who underwent spinal instrumentation, for instance, a lumbar drain is placed prophylactically if the soft tissue appears scarred and sparsely vascularized.