Management of Occult Spinal Dysraphism in Adults

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Chapter 183 Management of Occult Spinal Dysraphism in Adults

The tethered cord syndrome (TCS) results from relative fixation of, most commonly, the caudal spinal cord owing to one of multiple pathologic entities. This fixation prohibits normal physiologic motion, can cause focal ischemia and, in adults, most often manifests with back pain or a neurologic insult. TCS is generally diagnosed and treated during childhood, because most etiologies are congenital. The emergence of symptoms during adulthood has, however, become more commonly recognized. Although the underlying lesions are identical to those affecting children, the presenting symptoms often differ and their late emergence requires caregivers to closely consider whether the same surgical paradigms that are accepted in the pediatric population are applicable in adults.

In the adult population, TCS occurs in two general groups, those with a previously unrecognized congenital lesion and those who have undergone previous intradural surgery (acquired lesions), most commonly repair of a myelomeningocele. This chapter focuses on previously unrecognized congenital lesions.

Whether discovered during childhood or adulthood, congenital tethering lesions represent variants of occult spinal dysraphism (OSD). This chapter briefly discusses eight subtypes of OSD: fatty filum terminale, split cord malformation, lipomyelomeningocele, neureneteric cyst, dermal sinus tract and dermoid, terminal syrinx, meningocele manqué, and normally positioned conus with TCS symptoms. With regard to the management of adults who present with these malformations, the greatest challenge lies in recognizing symptoms and signs of this pathology as early as possible. Unlike children, who are often neurologically normal following treatment, many adults who are discovered to have OSD present with progressive neurologic deficits that may not be reversible and/or with life-altering pain that might not resolve postoperatively. The technical principles underlying surgical detethering in the adult population are identical to those used in the treatment of children with these lesions and are not discussed in detail here.

Embryologic Considerations

Differentiating the extremes of normal from subtle pathologic states is one of the most difficult aspects of managing patients who are at risk for TCS. When TCS was first described, clinically devastated patients with extreme caudal displacement of the conus medullaris into the sacrum from a thickened and unyielding filum terminale were easily differentiated from normal.^1,² However, the widespread use of magnetic resonance imaging (MRI) has allowed physicians to attempt to define a “normal” level of the conus medullaris in an adult. For some clinicians, below the L1–2 disc space is abnormally low, whereas for others, below the inferior border of L2 is abnormally displaced. This definition is confounded by the fact that in some cases, the conus medullaris, which normally has an anteroposterior diameter ranging from 5.0 to 8.0 mm, gently tapers into a very thick filum rather than demonstrating an obvious caudal tip.

The filum terminale and the distal conus medullaris are thought to arise through the process of secondary neurulation. Distally, the intradural filum terminale travels to fuse with the dorsal dura mater, usually in the midline, and then continues within a dural sheath as the coccygeal ligament to the dorsal coccyx. Historically, in the term infant, the inferior tip of the conus medullaris was described as being located at the L2–3 interspace in 98% of cases and at the L3 level in 1.2% of cases. Presumably, by 3 months of age the tip of the conus achieved its adult position by “ascending” to the L1–2 interspace. However, Wilson and Prince ³ concluded that a conus positioned at L2–3 should be considered normal at any age. Reimann and Anson⁴ compiled both their data and those from three other large series (a total of 801 adult spinal cords) to find that the conus medullaris is found above the L2–3 disc level in approximately 94% of cases, whereas the mean conus lies at the lower third of the L1 vertebra. Saifuddin and colleagues⁵ have also found that the mean termination of the conus is at the lower third of the L1 vertebra. It would be logical then to assume that tight fixation of the cord by the filum during in utero development would result in the most caudal position of the conus but that lesser degrees of tension would allow some cephalad migration. It might even be possible that mild tension on a relatively elastic cord could result in a relatively normal position of the conus. In such a case, symptoms, possibly secondary to persistent microtrauma, might not occur until adult life.

Presentation and Physical Examination

Although they harbor similar, or identical, pathology, adults with OSD tend to present with a different array of signs and symptoms than children. In children, cutaneous stigmata such as focal hypertrichosis, pigmented nevi, subcutaneous lumbosacral masses, and skin dimples are often observed. However, in the adult OSD population, these signs are present in only 36% of cases.⁶ Similarly, foot deformities are found in only 37% of adult patients.⁶

In the adult population, there is a slight female preponderance of congenital TCS, with ratios of 1:1.3 to 1:2.6, and the mean age at presentation is approximately 37 years.⁷^–¹⁰ Although there is no universally accepted classification system that stratifies adults with TCS, van Leeuwen and colleagues¹⁰ proposed that the origin of tethering might reasonably correlate with surgical outcomes and should be taken into account during surgical planning. Lee and colleagues¹¹ found satisfactory concordance between their experience and this classification scheme. Van Leeuwen’s scheme included four groups of TCS: post-repair myelomeningocele, tight filum terminale or filum terminal lipoma, Conus lipoma/lipomyelomeningocele, and split cord malformation (SCM).

The most common presenting complaint in adults with OSD is pain, which is encountered in as many as 80% of patients.⁶ The most common type of pain is insidious nonradicular back pain.^6,^9,^12,¹³ A thorough history might reveal that this pain has been present since childhood. Pang and Wilberger⁹ proposed three pathophysiologic mechanisms that led to the acute presentation of symptoms in 61% of their adult population with TCS. These mechanisms were transient stretching of the conus medullaris, narrowing of the spinal canal due to degenerative disease, and direct trauma. The added ischemia or mechanical distortion associated with these events is postulated to reveal symptoms in an already injured or stressed caudal spinal cord.

Adults also present with lower extremity symptoms, most commonly pain or weakness, or both. The weakness that results from distal spinal cord fixation is classically associated with both upper and lower motor neuron signs. Less common presenting signs and symptoms include changes in bowel and bladder function (approximately 69%⁶), scoliosis (8% to 31%,^6,¹¹ Fig. 183-1), and loss of lower extremity sensation resulting in foot ulceration (Fig. 183-2).

FIGURE 183-1 Severe atrophy of the lower extremities, notably in the gluteal musculature. This patient presented with a history of scoliosis and at operation was found to have a fatty infiltrated filum terminale.

FIGURE 183-2 A case of foot amputation in an adult with tethered cord syndrome who had a chronic history of anesthesia of the left lower extremity distal to the knee.

The physical examination findings that can be expected in a patient with TCS can be divided into cutaneous lesions, lower extremity findings, and changes in rectal tone. Although they may be encountered in the adult, the most telling findings (e.g., cutaneous stigmata and lower extremity asymmetry) are more common in the pediatric population. The cutaneous signatures of OSD include midline capillary hemangioma, subcutaneous lipoma, dermal sinus tract, caudal appendage, focal hirsutism, and atretic meningocele (Figs. 183-3 through 183-8). Cutaneous hemangiomas that may be common in other parts of the body are unusual in the lumbosacral region (see Fig. 183-3). In this area, especially in the midline, they have been associated with OSD and are often found in conjunction with other skin findings, such as focal hirsutism and subcutaneous lipomas. However, capillary hemangiomas are thought to be the least sensitive indicator of intradural pathology, with an approximately 10% incidence of associated intradural anomalies when seen in the lumbar region.¹⁴ Focal hirsuitism (see Fig. 183-4) should alert the clinician to the possibility of an underlying SCM or atretic meningocele (see Fig. 183-5).

FIGURE 183-3 Operative photograph demonstrates a flat capillary hemangioma of the midline lumbar spine. This patient was found to harbor a conus medullaris at the S1 vertebral level and a thickened fatty filum terminale.

FIGURE 183-4 Adult female patient with a history of severe back pain. Note the area of focal hirsutism, which was found to be associated with a split cord malformation.

FIGURE 183-5 A female patient with two cutaneous signatures. Note the area of hypertrichosis and a centered atretic meningocele.

FIGURE 183-6 An elderly patient with a history of leg length discrepancy, urinary dysfunction, and back pain. Note the subcutaneous mass and area of focal hirsutism. This patient was found to have a lipomyelomeningocele with dorsally tethering bands (meningocele manqué).

FIGURE 183-7 A patient found to have a subcutaneous mass and dermal sinus. At operation, both a dermal sinus tract and dorsal lipoma of the cord were found.

FIGURE 183-8 A large dermal sinus on the midline lumbar back of a 50-year-old man with back pain and increased sensory deficit of the lower extremities.

Typical lower extremity findings result from a combination of upper and lower motor neuron weakness in the legs without upper extremity symptoms. Such findings can manifest as decreased muscle bulk (Fig. 183-9) with increased or pathologic reflexes, and should alert the examiner to the possibility of TCS. Other findings include progressive arching of the feet and lower extremity size discrepancies (Fig. 183-10). The clinician should evaluate for hypalgesia of the lower extremities in patients with potential TCS. This sensory disturbance is often found in a patchy distribution.

FIGURE 183-9 Atrophy of the leg musculature in a 75-year-old woman with tethered cord syndrome. Note the forefoot amputation on the right side.

FIGURE 183-10 Foot length discrepancy in a 55-year-old adult with tethered cord syndrome.

Radiographic Assessment

Plain X-ray

Radiographs of the spine can localize spina bifida or possibly demonstrate an osseous median septum. Bony spina bifida occulta is seen in approximately 4% of the population but almost all patients with TCS have bony spina bifida occulta in the low lumbar region or sacrum, or both. Therefore, when seen in combination with symptoms consistent with TCS, the diagnosis must be considered.

Computed Tomography

CT offers greater detail regarding any osseous abnormalities and is generally indicated before surgical intervention, especially in the adult population where the diagnosis might not be straightforward. In certain cases, CT myelography may be indicated, because it can provide greater anatomic detail in cases of SCM.

Magnetic Resonance Imaging

Ideally, spinal cord tension and elasticity could be measured and assessed in an objective and noninvasive manner. Currently, this is not technically possible. MRI, therefore, represents the gold standard for visualizing the neural axis and soft tissue pathology related to OSD. Under the appropriate clinical circumstances, if the position of the conus is indeterminate (L3) or even above the L2–3 disc space, one should look for associated findings to help explain clinical symptoms. Even a small accumulation of fat within the filum should alert the clinician to the possibility of TCS. A successfully detethered spinal cord will not rise significantly within the spinal canal. Thus MRI is not a valuable tool for evaluating surgical outcomes.

Urodynamics

Urodynamic testing is important in establishing preoperative urinary function and is also employed during the follow-up period.

Pathologic Subtypes of Occult Spinal Dysraphism

Tight and Fatty Filum Terminale

The filum terminale is a structure usually less than 2 mm in diameter. If it is insufficiently elastic (e.g., abnormally thick or fat laden), this can limit the ability of the spinal cord to move cephalad with growth or movement, placing stress on the distal aspect of the conus medullaris (Figs. 183-11 to 183-13). Terminal syrinx, neurenteric cyst, dermal sinus tract and intramedullary dermoid, and SCM can all have an associated tight filum terminale, which must be sought at the time of surgical exploration.^1,^2,^15,¹⁶ Lipomatous infiltration ranges from small accumulations of fat in an otherwise normal filum to extensive involvement of the distal spinal cord. Incidental fat within the filum is seen in approximately 3.7% to 17% of the normal adult population.¹⁷ In one series, fat was found in 91% of patients with a tethered spinal cord.¹⁸ The lack of denticulate ligaments inferior to the origin of the T12 nerve allows relative mobility when caudally directed force is present in this region. Moreover, we have found that the denticulate ligaments, even cephalically, do little to abort either cranial or caudal traction on the spinal cord.¹⁹ By definition, the tight or fatty filum terminale originates below the level of the lowest nerve root origins. Additionally, this entity is not associated with a dorsal dural defect. These characteristics decrease the risk of neurologic injury or CSF leak when surgical detethering is performed.

FIGURE 183-11 T1-weighted axial magnetic resonance image of the lumbosacral spine. Note the fatty infiltrated filum terminale. The conus medullaris in this patient was at the L4 vertebral level.

FIGURE 183-12 Operative photograph of the filum terminale in the patient described in Figure 183-11.

FIGURE 183-13 Elongation of the spinal cord in a patient with a fatty infiltrated filum terminale.

Split Cord Malformation

Current nomenclature divides SCMs into types I and II.^20,²¹ The correlation between hypertrichosis and SCM is probably higher than any other single or combined cutaneous abnormality and underlying spinal cord lesion. The two dominant radiographic characteristics of a type I lesion are double dural tubes and an osseous or osseocartilaginous midline septum (Figs. 183-14 and 183-15). The type I septum almost always extends from the posterior surface of the vertebral body to the corresponding neural arch. Rostral to the septum, the hemicords may be separate for as many as seven vertebral levels. In this region, the two hemicords reside within a single thecal sac. The type II SCM is characterized by a single thecal sac.²¹ The cord may be tethered by nonfunctional nerve roots exiting from the medial aspect of either hemicord or by nonosseous median septum.

FIGURE 183-14 Type I split cord malformation. Note the hemicords separated by a bony septation.

FIGURE 183-15 T2-weighted sagittal magnetic resonance imaging of the lumbosacral spine of the patient described in Figure 183-14. Note the bony septation dividing the spinal canal into two compartments.

Between type I and II SCMs, there is a certain degree of crossover regarding these two features. Thus the SCM cannot always be classified radiographically before surgery. When discernible, the type II septum is usually at the caudal extreme of the split cord, where the hemicords appear to be closely opposed with the septum and with each other before rejoining into a single structure. In general, the hemicords in a type II lesion are much closer together and the split segment is much shorter than in a type I lesion.

At least one unrelated tethering lesion (i.e., fatty filum) is found in many lumbosacral and lower thoracic SCMs and in a much smaller number of cervical SCMs. The entire neural axis should be studied radiographically and if a second tethering lesion is found, it should be considered for treatment.⁷ The surgical outcome is generally excellent for SCM. The overall surgical morbidity is low but slightly higher with type I lesions (Fig. 183-16). The radiographic data on the split lengths when correlated with age, lesion type, and level of the septum are compatible with the hypothesis of an endomesenchymal tract transfixing the neural plate during early development of the neural tube.²¹

FIGURE 183-16 Operative photograph of the patient described in Figures 182-14 and 182-15. Note the two hemicords and the remains of the bony spicule.

Lipomyelomeningocele

The name lipomyelomeningocele emphasizes the two key characteristics of this lesion, which are adipose tissue within and/or adjacent to the spinal cord and an adjacent dural defect. Because of pathoanatomic variability, the literature classifying spinal lipomas includes multiple methods.²²^–²⁴ Chapman initially divided spinal lipomas into three categories and Pang further described them as dorsal, transitional, and caudal (terminal).^24,²⁵ Dorsal lipomas are unique in that the insertion of the fibroadipose stalk into the spinal cord occurs in an isolated segmental region, with normal cord and dura both above and below the lesion.²⁵ The rostral portion of the fibroadipose stalk of transitional lipomas inserts onto and blends with the dorsal surface of the conus medullaris (Fig. 183-17). Unlike the dorsal lipoma, however, the transitional lipoma remains intercalated with the nervous tissue all the way to the terminal aspect of the conus, where it joins with the filum, if present. Thus there is no normal spinal cord distal to the lipoma. The conus is commonly twisted within the caudal dural sac, which is often underdeveloped, infiltrated by fat, or frankly absent, complicating surgical closure. These lesions, therefore, present a unique surgical challenge and demand familiarity with the relevant anatomy. Terminal lipomas differ from dorsal and transitional lipomas by inserting into the caudal extremity of the conus or by replacing the filum without any direct infiltration of the spinal cord. There is no blending with the dorsal surface of the spinal cord. All sacral nerve roots leave the conus rostral to the lipoma. Almost invariably, the dura and overlying myofascial layers are intact.

FIGURE 183-17 Intradural component of a lipomyelomeningocele as seen on T1-weighted sagittal magnetic resonance imaging of the lumbosacral spine.

With the exception of terminal lipomas, patients with lipomyelomeningocele almost always have a cutaneous abnormality present from birth and therefore tend to come to clinical attention before adulthood (see Fig. 183-7). There is a female-to-male predominance of approximately 1.5:1.

When patients do not come to medical attention before adulthood, they most commonly present with insidious but progressive signs or symptoms. A small group, however, presents with acute symptoms, usually weakness or urinary incontinence. These are often not reversed with surgical intervention. Symptoms resulting from neurogenic bladder often take the form of incontinence or repeated bouts of urinary tract infection. Rectal incontinence does not occur without accompanying urinary incontinence. Other previously described signs and symptoms also manifest as a result of lipomyelomeningocele.

Neurenteric Cyst

Spinal neurenteric cysts are infrequently reported congenital abnormalities believed to be derived from an abnormal connection between the primitive endoderm and ectoderm. Neurenteric cysts are not confined to the spinal column (Figs. 183-18 through 183-20) but may be found within the brain, mediastinum, abdomen, or pelvis or even in a subcutaneous location. Intraspinal neurenteric cysts represent 0.3% to 0.5% of all spinal “tumors.”²⁶ They are, in fact, not tumors, which differentiates them from teratomas. Instead, these lesions are more similar to hamartomas, that is, displaced nests of endodermally derived tissue. The terminology for these lesions is problematic, because they have been reported as neurenteric cysts, enterogenous cysts, enteric cysts, gastrocytomas, dorsal enteric fistulas, split notochord syndrome, and teratoid cysts. Part of the challenge in naming these cysts is that they are not uniform, but instead likely represent a spectrum of lesions. A consistent association between neurenteric cysts and other forms of OSD has not been reported. A neurenteric cyst is classically reported as a solitary intradural, extramedullary lesion in the cervical region, located anterior or anterolateral to the spinal cord. The second most common location is thoracic, followed by lumbosacral. Osseous abnormalities, if present, are likely to involve the anterior spinal column. There is a male predominance of approximately 2:1. The most challenging technical problem for the surgeon results from the obligation to remove the entire wall of the cyst to prevent its reaccumulation.²⁶

FIGURE 183-18 Magnetic resonance imaging of a patient with an operatively confirmed neurenteric cyst.

FIGURE 183-19 Operative photograph of a lumbosacral neurenteric cyst.

FIGURE 183-20 A syringe filled with the mucin-laden material removed from the patient shown in Figure 183-19.

Dermal Sinus Tract/Dermoid

Dermal sinus tracts and associated dermoid tumors represent a common source of TCS in the pediatric population but are exceedingly rare in adults. In some cases, however, a patient has an incompletely treated DST that becomes symptomatic during adulthood. Therefore, symptoms consistent with TCS with a history of a “minor” surgical procedure during childhood should alert the clinician to the possibility of an incompletely treated DST or dermoid. Dermal sinus tracts can be encountered from the tip of the nose to the coccyx. In children, these entities are seen most commonly in the lumbosacral region (see Fig. 183-8), although many are appreciated in the occipital area. Cranial dermal sinus tracts normally travel inferiorly toward the deeper neural structures, whereas lumbosacral tracts ascend from their superficial origin to their deeper destination. Coccygeal tracts or “pits” end before the thecal sac and are regarded as innocent. An approximate incidence of coccygeal pits is 4% of the neonatal population²⁷ and that of DST has been estimated at 1/2500 births.²⁸ Although seemingly benign structures, these small communications between the superficial and deep derivatives of the ectoderm can result in tragic insult to the central nervous system if not adequately addressed. Perhaps reflecting a common ontogenic disorder, dermal sinus tracts are seen in 15% to 40% of split cord malformations. Approximately 60% of these tracts violate the spinal subarachnoid space and, of these, approximately one half attach to the conus medullaris, cauda equina, or filum terminale (Fig. 183-21). The literature supports a small male predominance. Connections between the skin and underlying structures usually occur in the midline but rarely are found in a paravertebral location. Common cutaneous findings seen in conjunction with dermal sinus tracts include flat capillary hemangiomas, focal hirsutism, and subcutaneous lipomas. In children, signs of local infection and/or drainage of debris or fluid from the surface of a tract should be considered suspicious for a DST.^7,¹⁴

FIGURE 183-21 Operative image of a patient with a dermal sinus tract and intradural dermoid.

Meningocele Manqué

Tethering bands from the spinal cord to the surrounding tissue, known as meningocele manqué, are a rare anomaly. Meningocele manqué is found in association with multiple other elements of spinal dysraphism, most classically with SCM and myelomeningocele. In both of these cases, the bands must be divided in order to complete detethering. The bands themselves are generally composed of nonfunctional neural tissue with dorsal root ganglion cells. They often penetrate the dura of an associated bony median septum or simply exit dorsally or, rarely, ventrally. On occasion, they pierce the dura and terminate on the undersurface of the lamina. The surgeon should be aware of this condition when removing lamina during an operation on a patient with OSD so as to not inadvertently put tension on the underlying cord or cauda equina. Meningocele manqué may be identified with MRI (Fig. 183-22) (linear and isointense with the spinal cord on T1-weighted images) but is often not appreciated owing to the small size of the bands. The bands are, however, easily demonstrable at operation.

FIGURE 183-22 T2-weighted axial magnetic resonance imaging demonstrates a dorsal tethering band (meningocele manqué).

Terminal Syrinx

The term terminal syrinx denotes a cavity found within the distal third of the spinal cord (Fig. 183-23). A terminal syrinx is seen in 10% to 30% of patients with TCS and is usually a secondary result of other pathologic processes causing TCS. Symptoms resulting from the syrinx, however, can bring the patient to medical attention before those resulting directly from the primary lesion. Although most classically seen with a syrinx, any intramedullary spinal cord lesion can interrupt or stretch crossing spinothalamic fibers in the anterior commisure of the spinal cord. This results in a dissociated and suspended sensory loss, particularly with diminished pain and temperature appreciation and preservation of position sense and light touch, because the latter fibers do not cross in the spinal cord.

FIGURE 183-23 T1-weighted sagittal magnetic resonance imaging illustrates a terminal syrinx.

These patients can develop painless injury in the feet or legs depending on the level of the syrinx. Patients might also complain of numbness as their primary symptom. By history, this numbness may appear to be radicular but is more commonly nondermatomal in nature. Symptoms generally begin distally, progressing in a proximal direction, and tend to be asymmetrical.

As the syringomyelia progresses, the patient can develop dysesthetic pain that is often deep and occurs in a nonradicular distribution. It has variously been described as “itching,” “burning,” or “deep and boring.” The symptomatology, especially pain, may be worsened by Valsalva maneuvers. Additionally, patients might note weakness of the lower extremities. As the condition progresses, the lower extremities can atrophy. Late in the disease, the deep tendon reflexes can disappear and fasciculations can develop in the affected muscles. Signs of upper motor neuron disease such as spasticity and hyperreflexia can affect the lower extremities. The Babinski reflex is usually positive. Bowel or bladder control is generally not affected until late in the progression of disease. The progression of syringomyelia occurs in an unpredictable fashion, but generally over many years. Neurologic worsening can either be gradual or stepwise but is rarely precipitous.

Outcomes following detethering vary depending on the time of intervention, nature of the TCS creating the syringomyelia, and location of the lesion. Asymptomatic patients may be followed without intervention, but outcome from treatment is directly related to preoperative disability. In adults especially, the collapse of the syrinx does not tightly correlate with the relief of symptoms. Using MRI in the acute postoperative period is of limited utility to evaluate the collapse of the syrinx, because it can take months for the syrinx to resolve. Shunting of the syrinx alone has produced a poor long-term outcome and is considered only as a last resort.

Conus in “Normal” Position with Symptoms of a Tethered Cord

Under most circumstances, the term tethered spinal cord implies an abnormally positioned conus medullaris. As discussed earlier, the inferior limit considered normal is not universally agreed upon. In the adult population, there is not a significant literature discussing patients who present with symptoms and signs consistent with TCS but imaging demonstrating the conus medullaris to be at a position accepted as “normal.” Several authors have established the presence of this entity in the pediatric population. ²⁹^–³² Multiple series have shown that incontinence in children who have essentially normal MRI scans of the lumbosacral region and usually have cystometrographic findings indicating a neurogenic bladder (hyperreflexic detrusor muscle) can be successfully treated by sectioning of the filum terminale.^{29–31,33–35} We strongly recommend that clinicians consider not only imaging findings but also clinical history, physical examination, and physiologic tests (e.g., urodynamics) when treating adult and pediatric patients who might have TCS.

Surgical Decision Making In Adult Tethered Cord Syndrome

In the pediatric population, surgical intervention for the treatment of OSD is widely accepted. There is no established consensus regarding the role of prophylactic surgery for adults with OSD. However, as demonstrated by Rajpal and colleagues,¹³ adults typically present with progressive symptoms that cannot be expected to abate in the absence of surgical intervention. Although progressive pain or neurologic deficits are indications for surgical intervention in the context of a suspected tethered spinal cord, some adult patients choose not to pursue surgical treatment.¹² The natural history of this subpopulation is not well defined.

As with the pediatric population, the objective of surgery for adults with OSD is to release the neural tissue from all points of fixation without sacrificing function. As previously mentioned, low-lying spinal elements will not rise within the spinal canal despite complete detethering. Postoperative imaging is, therefore, of little use in the assessment of operative goals. Although we do obtain MR imaging when evaluating potential recurrent tethering (to assess for syringomyelia), the decision to reoperate is almost exclusively based on history, examination findings, and physiologic testing (e.g., urodymanics).

The use of intraoperative physiologic monitoring in the adult TCS population has been promoted in multiple reports.³⁶^–³⁸ The combination of somatosensory evoked potentials with continuous and evoked electromyography can provide a high degree of sensitivity and specificity for identifying intraoperative neurologic injury during complex tethered cord release in adults³⁷ and should be considered. The use of a synthetic or autologous dural graft is left to the discretion of the surgeon. We favor a split lumbodorsal fascia graft, which is readily available in almost all patients.

Surgical Outcome

The likelihood of significant reversal of lost neurologic function in adults with TCS is not entirely predictable, but in general, longer duration and greater severity of a deficit are associated with a lower likelihood of postoperative resolution. Overall, rates of surgical success are comparable to those reported in pediatric series.⁸ Recent literature reviews by Aufschnaiter and colleagues⁶ and Lapsiwala and Iskandar⁸ demonstrated that pain improved in 81% to 89% of patients and stabilized in an additional 15% to 17%. Sensorimotor symptoms improved in approximately 50% of patients and stabilized in 25% to 50%. With regard to back pain specifically, reported rates of postoperative improvement range from 50% to 83%.^9,^12,¹³ Although improvement in bowel and bladder function is unpredictable,^6,³⁹ reported rates are as high as 38.5%.⁹ Worse outcomes have been associated with SCM and lipomyelomeningocele.^6,¹⁰ Consistent with previous findings, patients with a longer duration of symptoms, previous surgery, or rapidly progressive motor weakness also had worse outcomes. There is a nontrivial rate of symptom recurrence following an initial response to surgery, with rates ranging from 5% to 17%, depending upon the specific symptom.¹³