Syringomyelia

Etiology

Syringomyelia develops due to a disturbance in CSF flow dynamics,[9] often resulting from spinal subarachnoid space obstruction in most cases.

Classification of Syringomyelia

Communicating: This is characterized by central canal dilatation that communicates with the fourth ventricle and is invariably associated with hydrocephalus. The cavity of the syrinx features an ependymal lining.

Non-communicating (isolated): This involves dilations of the central canal resulting from altered CSF flow dynamics within the spinal subarachnoid space resulting from CM-1, basilar impression, and arachnoiditis. These dilations tend to dissect paracentrally into the posterolateral quadrant of the spinal cord.

Extracanalicular: This is observed in the watershed area of the spinal cord following trauma or strokes and is characteristically associated with myelomalacia. These syrinx cavities are lined with glial or fibroglial tissue.[10][11]

Types of Syringomyelia or Hydromyelia

Non-communicating syringomyelia is the most common type of syringomyelia.

• Type I: This type of syringomyelia arises due to obstruction at the foramen magnum and subsequent dilation of the central spinal canal caused by conditions such as CM-1, basilar invagination, and other lesions.

• Type II: This type of syringomyelia occurs without any obstruction at the foramen magnum, and is often considered idiopathic.

• Type III: Syringomyelia results from lesions directly affecting the spinal cord, including tumors, traumatic myelopathy, spinal arachnoiditis, pachymeningitis, and myelomalacia.

• Type IV: Pure hydromyelia.[12]

 Etiologies of Syringomyelia

• Cranio-cervical anomalies: These include CM-1 and basilar impression. CM-1 represents the most frequent cause,[9] with syringo-hydromyelia reported in 23% to 80% of CM-1 patients according to current literature.

• Other causes: These include tumors, trauma leading to dorsal arachnoidal webs, arachnoiditis, meningitis, postoperative scarring, and dysraphism.[13][14][15][16]

 Intradural Pathologies Obstructing the CSF Flow

• Tonsils occupying the foramen magnum and overlying foramen of Magendie, medialized tonsils, tonsillar gliosis, and tonsillar hypertrophy

• Dural scarring

• Arachnoid veil, webs, adhesions, and thickening

• Vermian branch of the posterior inferior cerebellar artery

• Cisterna magna cyst [17][18]

Epidemiology

The prevalence of CM-1 ranges from 3 to 8 per 100,000 individuals, with syringomyelia diagnosed in 65% of CM-1 patients.[9] The reported prevalence of syringomyelia in the literature ranges from 8.4 per 100,000 to 0.9 per 10,000.[14] A study in Italy reported a prevalence of 4.84 per 100,000 with an incidence of 0.82 per 100,000. Among Caucasians, the prevalence is reported as 5.4 per 100,000, while in Japan, it is 1.94 per 100,000.[12]

Approximately 22.7% of patients with syringomyelia are asymptomatic. In operative series from the United States and Europe, the peak ages of presentation for CM-1 were 8 in pediatric cases and 41 in adult cases. The incidence of syringomyelia in these studies was 65%.[19] With the rise in radiological imaging, incidentalomas are increasingly being detected.[20]

Pathophysiology

Authors have proposed various theories to explain the origin and progression of syringomyelia. 

• Gardner and Angel introduced the "hydrodynamic theory," suggesting that hindbrain hernias obstruct normal CSF egress, causing fluid to divert into the central spinal canal and pulsate with each heartbeat, which is also known as the "water-hammer" effect.

• Williams observed pressure gradients exceeding 100 mm Hg across the foramen magnum during Valsalva maneuvers in patients with hindbrain hernias. He hypothesized that this pressure difference creates a suctional force ("suck") that draws ventricular CSF into the syrinx cavity. The fluid's entry impacts and rebounds ("sloshes") off the caudal and then rostral walls of the syrinx, akin to water behavior in an elastic balloon squeezed at one end. Although subsequent authors noted the lack of communication between the syrinx and the fourth ventricle, recent dynamic MRI studies have provided evidence supporting this theory. The slow caudal growth of a syrinx may be a result of approximately 42 million such impacts in a year.

• Ball and Dayan proposed that increased spinal CSF pressure, particularly during coughing or sneezing in patients with foramen magnum obstruction, drives CSF through para-vascular Virchow-Robin spaces along the spinal cord surface.

However, large-scale physiological studies have yet to confirm or refute these 3 proposals definitively.

• Oldfield et al proposed that a CSF pressure wave generated by the systolic "piston-like" caudal displacement contracts the cord, forcing fluid into the syrinx cavity from the spinal subarachnoid space. Critics argue that fluid cannot enter a contracted cord. Although dynamic MRI studies have shown downward tonsillar movement during systole, confirming trans-parenchymal CSF movement on Cine MRI remains elusive.

• Gretiz, Koyanagi, and Houkinkoya have proposed a theory supporting the extracellular nature of syrinx fluid rather than CSF. Abnormally rapid movement of CSF past the cord causes a low-pressure zone within the cord, promoting extracellular fluid build-up and syrinx formation.[3][21][22][23][24][25][26][27][28]

Although the pathophysiology concerning the origin of syringomyelia remains an elusive Gordian knot, the pathophysiology underpinning progressive syrinx enlargement may have a common theme.[29]

Development in the Pathogenesis of Syringomyelia

Classic communicating: Classic communicating theory posits that there is anatomical communication between the syrinx and the fourth ventricle.

Gardner and Angel postulated that atresia of the foramina of the fourth ventricle causes systolic “water hammer” from pulse wave, causing hydromyelia and herniating structures through the foramen magnum to act as a one-way pump and valve. This later ruptures the ependymal lining and diverticulum into the cord parenchyma, causing syrinx formation.[21]

In contrast, Williams argued against systolic pulse waves directly causing syringomyelia. He suggested that obstruction at the foramen magnum creates a craniospinal pressure dissociation, generating a "suck" effect. This disrupts normal CSF flow into the spinal subarachnoid space, redirecting it through the obex. The longitudinal intra-cavitary fluid motions, referred to as "slush," help in maintaining the syrinx.

Du Boulay supported the idea of 2 intracranial CSF pulse waves contributing to the systolic pulse wave in the absence of ventricular atresia. The ventricular pulse wave corresponds to the systolic pulse wave, whereas the cisternal pulse wave, the first pulse wave exiting the foramina of the fourth ventricle, also propagates into the spinal subarachnoid space.

Transmedullary infiltration: Subsequently, it was evident that anatomical communication between the syrinx and the fourth ventricle is rare.

Ball and Dayan observed that CSF pulse waves are typically insufficient to form a syrinx by entering an open central canal. They proposed that in cases of foramen magnum obstruction, a Valsalva-like maneuver leads to "craniospinal pressure dissociation," causing CSF to enter the spinal parenchyma via the perivascular space (Virchow-Robin spaces). Occasionally, the syrinx may rupture into the ependyma.[26]

However, Oldfield et al contested this theory by demonstrating compression of the upper part of the syrinx during systole. According to Oldfield, cerebellar tonsils acting as pistons generate pressure waves, forcing CSF into the parenchyma. This "Piston theory" gained support from subsequent work by Heiss.

Parenchymal formation: The pressure within the syrinx is observed to be equal to or higher than that in the spinal subarachnoid space, contradicting the transmedullary theory. Current understanding posits that the syrinx is a blood plasma "ultra-filtrate," a concept first proposed by Klekamp. The increased CSF flow resistance results in a disequilibrium between CSF and the intramedullary extracellular fluid exchange that typically occurs through the perivascular spaces.

Stoodley et al proposed that the volume and pressure of the cyst play crucial roles in regulating the balance between the inflow and outflow of CSF through the perivascular spaces.[30] Levine advocated for the concept of the spinal subarachnoid space and the neuroaxis venous system, which comprises two fluid columns in hydrostatic equilibrium. In cases of foramen magnum obstructions, the "transmural pressure displacement" leads to mechanical stress on the venous system, causing disruption to the blood-spinal cord barrier and resulting in leakage of an ultrafiltrate of blood, which contributes to syrinx formation.

Koyanagi and Houkin’s theory postulated that the reduced spinal subarachnoid compliance primarily impacts the posterior spinal veins, which lack a pial covering and are situated directly in the subarachnoid space. This disruption of Starling's equilibrium leads to intramedullary edema and eventual syrinx formation.[28]

Clinicopathological correlation: The primary pathology in syringomyelia involves a gradually enlarging cavity within the central spinal canal. This expanding CSF-filled "syrinx" compresses the spinothalamic tract neurons that cross in the anterior white commissure. However, the posterior columns remain unaffected due to their more distal location. Consequently, there is a loss of pain and temperature sensation with preserved touch and vibratory sense, leading to segmental dissociated sensory loss. This sensory loss predominantly affects the upper limbs in a "cape-like" distribution, with sensory deficits mainly observed in the shoulder area.

The natural history of CM-1 with syringomyelia is usually benign, as only a small fraction of patients treated non-surgically eventually require surgery.[20] Ependymal ciliary movement is regulated by Connexin 43 (Cx43) and actin. Studies using a rat model have demonstrated the loss of Cx43 at the site of compression, leading to the disarray of the actin network and exposing centrioles to CSF shear stress.

Basilar invagination, Chiari formation, and syringomyelia also result from atlantoaxial instability.[31] Cranio-cervical junction osseous anomalies and a skull base angle of >135° predict syrinx formation. The extent of tonsillar herniation was a determinant of cervical syrinx formation.[32]

Syringomyelia is associated with bony-posterior fossa volume, mean velocity, and the net flow of CSF at the craniovertebral junction.[33] Studies have shown that the earlier arrival and peak velocity of caudal CSF flow are associated with an increased risk of syringomyelia in CM-1 cases.[34]

History and Physical

As syringomyelia is commonly associated with CM-1, examining related clinical features is crucial.

• Tussive headaches: Coughing (Valsalva maneuvers) causes sudden increases in intracranial CSF volume, resulting in transient suboccipital headaches and neck pain a split second after a cough. The features of Chiari headaches are listed below.
  • Site: Sub-occipital
  • Mode of onset: Sudden 
  • Nature/character: Heavy, crushing, pressure-like, occasionally pounding when severe but otherwise non-throbbing
  • Radiation: Radiates to the vertex, behind the eyes, and inferiorly to the neck and shoulders
  • Duration: Brief, lasting only seconds
  • Exacerbated by: Physical exertion, Valsalva maneuvers, head dependency, and sudden changes in posture

• Hoarseness, dysphagia, coughing with swallowing due to downward traction on lower cranial nerves and brainstem compression.

• Visual disturbances: Retro-orbital pressure and pain, along with various visual phenomena such as flashing lights, floaters, blurred vision, photophobia, and diplopia. The clinical examination may reveal possible horizontal, rotatory, or down-beat nystagmus due to the involvement of brainstem vestibulo-ocular connections.

• Oto-neurological symptoms: Dizziness, tinnitus, ear pressure, decreased hearing, oscillopsia.

• Cerebellar disturbances: Tremors, dysmetria, ataxia, gait, and balance issues.

• Syncope

• Sleep disturbances: Snoring, sleep apnea, and palpitations due to brainstem compression.[6][35]

Features resulting from the syrinx depend on the anatomical level and include the following conditions:

• Paresthesia/hyperesthesia is the most common sensory symptom, followed by non-radicular segmental pain.[6] Segmental dissociated sensory loss involves loss of pain and temperature sensation but preserves touch and vibratory sense, often manifesting in an upper limb "cape-like" distribution. Lack of pain perception may lead to injuries and chronic skin ulcerations on the hands.

• Muscle weakness and impaired fine motor function may progress to atrophy of intrinsic hand muscles due to damage to anterior horn cells (lower motor neurons) at the syrinx level, potentially resulting in a "claw hand" deformity.

• Spasticity in lower limbs due to syrinx expansion may compress or damage adjacent lateral corticospinal tracts (upper motor neurons).

• Progressive scoliosis resulting from injury to anterior horn cells innervating the paraspinal axial musculature.

• Horner syndrome, which may be observed in cervical or upper thoracic syringes.

• Poorly localized non-radicular segmental neuropathic pain, possibly related to substance P.[36][37]

The presentation of syringomyelia is highly variable, with patients reporting symptoms such as pain, muscle weakness, particularly in the hands and arms, temperature insensitivity in the upper limb, spasticity or stiffness in the lower limbs, and progressive scoliosis. The clinical course typically progresses over months to years, initially experiencing rapid deterioration that later slows down.[5] A linear relationship is observed between cyst morphology, symptom duration, and severity.[38][39] In cases where associated CM-1 is present, patients may also experience occipital headaches (precipitated by coughing, straining, and sneezing), neck pain, gait, balance problems, dizziness, hoarseness, and swallowing difficulties, as well as sleep disturbances such as snoring.

In patients with syringomyelia secondary to foramen magnum obstruction who undergo treatment with a syringosubarachnoid or thecoperitoneal shunt, an improvement in spasticity exists despite the worsening of other neurological functions. This observation suggests that the spasticity in the limbs may be attributed to the bulk of the syrinx rather than brainstem compression at the level of the foramen magnum.[40]

Classic symptoms such as suspended sensory loss, segmental weakness, and burning sensations are not universally observed in all patients with syringomyelia. The initial symptoms before intervention play a crucial role in predicting the outcome. Dissociative sensory loss typically occurs in cases of centrally located syringomyelia, resulting from the involvement of the gray commissures in lamina X. Patients may also experience autonomic bladder dysfunction. Bowel dysfunction is uncommon until the late stages of spinal cord dysfunction, which is secondary to the involvement of the Clarke nucleus in lamina VII, containing neurons of pre-ganglionic autonomic fiber origin, as well as laminae VIII and IX, associated with modulating skeletal muscle motor function.

The most common symptoms of syringomyelia include radicular pain, gait ataxia, sensory disturbances, dysesthesias, motor weakness, spasticity, autonomic dysreflexia, and neuropathic pain.[12][41]

As syringomyelia progresses, spasticity tends to increase. The progression of the condition is typically slow, with the clinical symptoms often remaining stable for years.[42]

Evaluation

Magnetic Resonance Imaging

MRI, with and without contrast, is the preferred imaging modality (see Image. Syringomyelia Visualized on MRI in a Patient With Hindbrain Herniation). The scan allows for precise delineation of relevant anatomy and accurate visualization of the syrinx in both sagittal and axial planes. MRI quickly reveals crucial information such as the syrinx cavity's location, size, and extent, along with assessing the degree of cerebellar tonsillar ectopia (see Image. Syrinx Visualized on MRI in a Patient With Basilar Invagination).

A ubiquitous feature in patients with associated CM-1 is the compression of retro-cerebellar CSF spaces, which can be clearly observed on MRI. Furthermore, MRI aids in ruling out cystic lesions or spinal tumors and can detect leptomeningeal enhancement indicative of infection, as well as arachnoid scarring. Longitudinal MRI studies can also track syrinx progression over months or years, providing valuable insights into the natural history of syringomyelia (see Image. Holocord Syrinx Visualized on MRI in a Patient With Chiari Malformation).

Dynamic MRI or Cardiac-Gated Cine MRI Flow Study

Phase-contrast MRI is used to study the disturbance of CSF dynamics in detail. This imaging technique enables noninvasive analysis of CSF hydrodynamics, diagnosing velocity or flow disturbances at the foramen magnum (especially in patients with <5 mm tonsillar ectopia), visualizing spinal cord wall motion, and detecting syrinx fluid motion during both cardiac systole and diastole at rest.[6][29] In addition, it proves valuable in documenting postoperative CSF flow changes and objective improvements.

Myelography with High-Resolution Computed Tomography Scan

This imaging modality is recommended in cases where MRI is contraindicated, such as in patients with metallic joint implants or cardiac pacemakers. Delayed computed tomography (CT) scans can effectively visualize dye leached into the syrinx cavity. However, some authors have criticized CT myelography for its low sensitivity in detecting CSF blockage.[43]

Although electromyography lacks diagnostic value in syringomyelia, it helps rule out peripheral neuropathy as a cause of paresthesias.

The configuration of syrinx can be categorized into 4 types—distended, moniliform type (continuous septations ≥3), slender type, and circumscribed.[44]

Treatment / Management

Treatment strategies for syringomyelia include avoiding activities that increase venous pressure, such as straining, flexing the neck, and breath-holding spells, which can help alleviate symptoms by reducing pressure.

Spontaneous resolution of syringomyelia is common among children as their skulls grow and CSF flow is restored. In adults, spontaneous resolution can occur due to various factors, such as the spontaneous rupture of arachnoid adhesions, drainage of the syrinx into the spinal subarachnoid space, or brain atrophy in older patients.[30] Surgical interventions aim to correct the underlying pathophysiology causing syringomyelia, with the primary goal of improving CSF flow dynamics.(B3)

In patients with CM-1, craniocervical decompression is often the recommended approach.[1] This consists of suboccipital craniectomy and removal of the posterior arch of C1, opening the dura and arachnoid, and resection of arachnoid adherences when present.[45] Essentially, this surgical intervention creates an artificially enlarged cisterna magna. Intraoperative ultrasonography can be used to confirm the decompression of the tonsils and ensure pulsatile CSF flow around the craniovertebral junction. The duration of sensory deficits before surgery significantly predicts symptomatic improvement following surgery. Studies have shown that a shorter duration of preoperative symptoms has better outcomes. Therefore, early surgical intervention is crucial to minimize deficits and improve overall outcomes.(B3)

In patients with postinflammatory arachnoid scarring and posttraumatic syringomyelia, the operative procedure is directed toward reconstituting spinal subarachnoid CSF flow by arachnoid scar membrane resection, microsurgical lysis of arachnoid adherences, and dural reconstruction.[46][47](B2)

Shunts are typically considered for idiopathic syringomyelia or in cases where patients have not responded to other treatments. The syringosubarachnoid shunt is the most commonly used shunt procedure, with the syringoperitoneal shunt being an alternative if the former fails. Although some studies suggest better outcomes with the syringosubarachnoid shunt compared to foramen magnum decompression, this recommendation is not universally recognized.[39][48][49] Shunts are generally not preferred and are considered a last resort due to their high complication and failure rates, as well as their inability to address the underlying cause of syringomyelia. (B2)

Surgical Indications

• Symptomatic CM-1-A (CM-1 with syrinx)

• Asymptomatic CM-1-A with a holocord syrinx, clinical-radiological worsening, central syringe with Vaquero index >0.5 or eccentric syringe, and concurrent syringobulbia

• Symptomatic isolated syringomyelia with no consensus for surgery

• Posttraumatic syringomyelia with motor deficits

The key surgical interventions involve osseo-dural decompression of the posterior fossa and complete release of obstruction at the foramen magnum and foramen of Magendie.[12][17] Atlantoaxial stabilization has shown clinical improvements and restoration of spinal alterations and abnormal curvatures.[50](B3)

PPreoperative assessment of intracranial compliance is essential. Patients with low intracranial compliance who undergo treatment with a ventriculoperitoneal shunt before foramen magnum decompression demonstrate regression of syringomyelia in nearly 80% of cases.[51] The use of a fourth ventricle to spinal subarachnoid space stent has been recommended for refractory cases and in tetra-ventricular hydrocephalus.[52][53](A1)

Treatment Modalities

Various treatment modalities are listed below.

• Foramen magnum decompression is typically combined with duraplasty, arachnoid opening, widening of the foramen of Magendie, or tonsillar resection. Obex plugging is less commonly used to prevent the "water hammer" effect.

• If hydrocephalus is also present, shunting or endoscopic third ventriculostomy is used as the initial treatment to relieve pressure on the cerebellar tonsils.

• Endoscopic fenestration of a cystic fourth ventricle or a cyst in the posterior fossa can be considered part of the treatment plan.

• Any relevant spinal pathologies, such as untethering the tethered cord, are addressed. If these interventions are insufficient, additional syrinx shunting procedures may be necessary.

Differential Diagnosis

The differential diagnosis should include the conditions mentioned below.

• Spinal intramedullary tumors, such as hemangioblastoma, ependymoma, and gliomas, may secrete exudative fluid with a high protein content, leading to microcysts that can eventually coalesce. While most intramedullary tumors enhance on contrast MRI (a syrinx does not enhance on contrast MRI), a true syrinx can occur within a tumor.

• Spinal intramedullary cysts, myelomalacia, arachnoid cysts, and glioependymal cysts.

• Residual central spinal canal: The central canal of the spinal cord may involute with age, and a persistent central canal is not considered an anomaly.

Prognosis

Professionals continue to grapple with the elusive natural history of syringomyelia, characterized by its unpredictable and highly variable course, making accurate prognostication challenging. The prognosis hinges on factors such as the underlying cause, the extent of neurological impairment, the location and size of the syrinx cavity, and a syrinx diameter exceeding 5 mm, along with associated edema, which often predicts rapid deterioration. The rarity of the condition, its variable progression, and limited follow-up periods further complicate treatment assessment.[54] However, early surgical intervention is associated with reduced deficits and improved outcomes.

Most studies (99%) have reported using posterior fossa/foramen magnum decompression as the primary surgical intervention. Postoperatively, syringomyelia improved or resolved in nearly 80% of patients.[19] Small-bone-window posterior fossa decompression with duraplasty has emerged as an effective and safe treatment option with a low complication rate.[55] Foramen magnum decompression and duraplasty have shown significant and sustained improvements in both clinical and radiological outcomes. Paradoxically, no association with clinical outcomes exists concerning regression of the syrinx or alterations in the position of the cerebellar tonsillar.[56] The restoration of CSF flow at the craniocervical junction has demonstrated a stronger correlation with improved outcomes following posterior fossa decompression with duraplasty compared to factors like the fourth ventricle area and Vaquero index (syrinx to cord ratio).[57]

The Chicago Chiari Outcome Scale score was also better in the posterior fossa decompression and resection of the tonsils group.[58][59] A recent systematic review and meta-analysis demonstrated a clinical improvement rate of 86.8% in the posterior fossa decompression with duraplasty group compared to 69.8% in the posterior fossa decompression cohort. Medullary decompression and occipital-cervical sagittal realignment have shown resolution of syringomyelia.[60] Foramen magnum decompression with dural patch grafting has exhibited better functional outcomes than dural dissection. Recent meta-analyses highlight the superiority of autologous grafts over non-autologous options in terms of complications.[30] Dura splitting decompression is comparable to posterior fossa decompression with duraplasty in terms of clinical improvement while significantly reducing operative time, hospital stay duration, and CSF-related complications such as CSF leak, meningitis, and pseudomeningocele.[61]

Size, length, and number of syringomyelia are not critical to prognosis. However, size reduction of the syrinx confers high chances of motor improvement compared to sensory disturbance and pain.[62] Motor dysfunction, brainstem herniation, and basilar invagination are predictors of poor clinical prognosis.[55] Autonomic dysfunction and non-cervical site of the syrinx and motor impairments have an unfavorable functional outcome. Cervical syringomyelia, in particular, has the potential for strong functional recovery after adequate intervention, probably owing to minimal CSF pressure caused by gravity compared to thoracic and lumbar areas.[10]

A moniliform variant of posttraumatic syringomyelia shows a better prognosis.[44] Posttraumatic syringomyelia typically affects individuals aged 30 and older with complete spinal cord injury and commonly involves the cervical spine within 5 years post-injury.[63] A systematic review of posttraumatic syringomyelia involving 1803 patients found that the time from spinal cord injury to syringomyelia diagnosis ranged from 42 to 264 months. Surgical management, primarily arachnoid lysis and syrinx drainage, was performed in nearly 90% of cases, with a complication rate of 26%. Postoperative symptom improvement was observed in 43% of patients.[64] The 10-year survival rate among cohorts with syringomyelia following traumatic spinal cord injury is approximately 70%.[65]

Prophylactic neurosurgery may offer benefits in reducing the necessity for spinal curvature correction surgery in patients with a large syrinx (syrinx/cord or S/C ratio >0.7).[66]

Despite undergoing posterior fossa decompression, persistent, recurrent, or worsening syringomyelia may occur in 10% to 50% of cases. They can be categorized into:

• Group I: Cases with insufficient decompression may require repeat posterior fossa decompression or dredging of the foramen magnum and foramen of Magendie.

• Group II: Cases involving craniocervical instability may necessitate atlantoaxial fusion surgery.

• Group III: Cases related to local spinal pathologies such as fractures, tumors, and cysts may be managed with modalities such as ventriculoperitoneal shunt, syringo-subarachnoid shunt, and pulsed radiofrequency treatment.[13]

Complications

Myelopathy is a significant complication resulting from the disease process. It can lead to spasticity, which may progress to paraplegia/quadriplegia, decubitus ulcers, recurrent pneumonia, and bowel and bladder dysfunction. Additional complications include neuropathic pain and neuro-arthropathy.

Kyphoscoliosis is the result of a reduction in spinal length.[67][68]

Postoperative complications have been reported in 41% of cases in one series, with the most common complications being CSF leak, pseudomeningocele, aseptic meningitis, wound infection, meningitis, and neurological deficits, resulting in a mean complication rate of 4.5%. Mortality rates were found to be 11% in the same study, with no observed difference between pediatric and adult series.[19]