Spontaneous cerebrospinal fluid hypotension as a cause of progressive tonsillar descent and syrinx formation 12 years after uncomplicated Chiari decompression

INTRODUCTION

Chiari malformation type I (CMI) has an incidence of 1/1000 births and remains a frequent condition treated by pediatric neurosurgeons.^[1] CMI is described as cerebellar tonsil descent at least 5 mm below the level of the foramen magnum.^[2] Although the pathophysiology of CMI is multifactorial and incompletely understood, posterior fossa hypoplasia and subsequent cerebellar crowding is the most implicated etiology.^[3] This can lead to obstruction of cerebrospinal fluid (CSF) flow, compression of cerebellar parenchyma, and the classic symptoms associated with the condition.^[2]

Patients with symptomatic CMI are surgically treated with decompression of the foramen magnum. Chiari decompressions historically have a low complication rate and are successful at reducing symptoms.^[1] While persistence of Chiari symptoms after decompression without clear morphologic recurrence has been described, true tonsillar descent following successful surgical treatment has not been documented.^[4]

A dural defect can cause CSF leakage into the extradural space from the spinal canal, leading to a drop in intracranial pressure (ICP). This reduction can cause low and negative intradural pressures, resulting in progressive tonsillar descent, mimicking the presentation of CMI.^[5] While there is potential for misdiagnosis between CMI and spinal CSF leak, the pathologies are unrelated and occur independently of each other, and the two have seldom been observed in the same patient.^[6]

Herein, we report the case of a 14-year-old female who presented with persistent headaches, cerebellar tonsil descent, and syrinx formation 12 years after an uncomplicated Chiari decompression. Initial radiographic and clinical interpretation raised suspicion for CMI recurrence, but subsequent evaluation suggested SIH secondary to spontaneous CSF leak. An empirical epidural blood patch (EBP) was performed, which led to resolution of symptoms, stabilization of tonsillar position, and syrinx regression. To the best of our knowledge, this is the first reported case of symptomatic tonsillar descent and syrinx formation due to SIH more than a decade after uncomplicated Chiari decompression.

CASE REPORT

A 14-year-old female with a body mass index of 18.4 presented to the clinic with a 2-month history of worsening, throbbing, diffuse headaches. Her past medical history was significant for CMI deformity without syrinx, treated by suboccipital craniectomy with C1 laminectomy and expansile duraplasty at age 2 [Figure 1]. She reported being active, engaging in sports, and a weightlifting regimen.

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Figure 1:

Brain and cervical spine magnetic resonance imaging, mid-sagittal T2-weighted series, showing stable post-surgical changes following Chiari decompression, performed 4 years before presentation. No syrinx is visible.

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Although the headaches did not appear related to her previous CMI, a magnetic resonance imaging (MRI) of the brain and cervical spine with CSF flow study was performed. The MRI demonstrated stable post-surgical changes of prior surgical decompression of the craniocervical junction with low-lying cerebellar tonsils 14.42 mm below the foramen magnum, unchanged from an examination taken 8 years prior [Figure 2a and b]. There was no evidence of hydrocephalus or pseudomeningocele, but a hypoplastic left transverse sinus was noted, which was seen in previous studies. The CSF flow study demonstrated normal flow through the anterior craniocervical junction with decreased flow through the posterior junction. Flexion X-rays ruled out craniocervical junction instability. Due to crowding at the foramen magnum and diminished retro-cerebellar CSF flow, the patient was advised to significantly diminish strenuous activities and instructed to return if symptoms worsened. Nine months later, the patient presented with worsening symptoms, she described as frequent, severe bitemporal headaches with associated eye pain that was somewhat relieved with acetaminophen. Further investigation was recommended, and she was referred to ophthalmology, where papilledema was ruled out. X-ray, MRI venogram, MRI angiography, and thoracic and lumbar spine MRI were unremarkable. MRI of cervical spine demonstrated asymmetric tonsillar ectopy more prominent on the right than left, and presence of a syrinx at the inferior aspect of C2 measuring 4.7 mm in length and 2.6 × 2.7 mm in cross-sectional diameter [Figure 3]. The CSF flow study showed diminished anterior flow with no appreciable posterior flow at the craniocervical junction.

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Figure 2:

(a) Brain and cervical spine magnetic resonance imaging, mid-sagittal T2-weighted series, demonstrating low-lying cerebellar tonsils below the craniocervical junction (yellow arrow), unchanged from prior imaging. (b) Phase-contrast cerebrospinal fluid flow study, mid-sagittal orientation, demonstrating diminished posterior flow (red arrow) at the craniocervical junction.

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Figure 3:

Cervical spine magnetic resonance imaging, mid-sagittal T2-weighted series, showing syrinx (red arrow) at the inferior aspect of C2 vertebral body.

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One month later, she presented to the emergency department with a severe headache in the bilateral temporal-parietal region that only improved laying down flat. She reported dizziness and clumsiness with the headaches. Her guardian noted snoring and fatigue. The MRI taken revealed further tonsillar descent with abnormal, pointed morphology, and no other changes.Given her progressive symptoms, postural headaches, and history of strenuous weightlifting, SIH with spontaneous or trauma-related CSF leak was proposed.

The patient returned 9 days later, and an ICP monitor was successfully placed with verified low intraoperative CSF loss. The ICP monitor showed low and negative pressures and clearly provoked a headache with the vertical position. The patient then received an empirical EBP at L3/L4 without the use of diagnostic approaches for leak localization, such as MRI with gadolinium contrast or CT myelography. The procedure was successful, and the patient presented for a follow-up 2 weeks later with demonstrated change to positive ICP and resolution of her headaches.

Six months after the EBP, MRI confirmed a stable cerebellar tonsillar position and shrunken cervical syrinx [Figure 4a and b]. The patient was asymptomatic except for rare headaches that were not particularly bothersome. She was cleared for sports but advised to avoid weightlifting to prevent another potential CSF leak.

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Figure 4:

(a) Cervical spine magnetic resonance imaging, mid-sagittal T2-weighted series 6 months post-epidural blood patch, demonstrating resolution of cervical syrinx and stable cerebellar tonsillar position. (b) Phase contrast cerebrospinal fluid (CSF) flow study, mid sagittal in-plane image, demonstrating increased CSF flow at the anterior and posterior craniocervical junction.

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DISCUSSION

The curative treatment for CMI provides decompression of the foramen magnum by a suboccipital craniectomy at the C1 posterior arch, often done with a duraplasty. The procedure is indicated for individuals with tonsillar descent >5 mm below the foramen magnum and worsening symptoms. The goal of the procedure is to restore CSF levels and flow across the foramen magnum to optimal levels.^[1] CSF leak is known to be an acute complication of Chiari decompression; however, it occurs at the operative site in the postoperative period. Meticulous dural closure and intraoperative Valsalva can substantially lower the risk. Long-term complications are most commonly due to pseudomeningocele formation, inadequate restoration of craniocervical CSF flow, cervical spine instability, and inappropriate craniectomy size. No long-term association has been made between Chiari decompression and spinal CSF leak.^[7]

Spinal CSF leaks most commonly occur due to a dural tear near the dural sleeves surrounding spinal nerve roots. The dura may rupture due to several inciting causes, including sneezing, high-exertion activity, and blunt trauma.^[8] Bearing down while weightlifting can drastically elevate intradural CSF pressure, thus increasing the risk of CSF leak.^[9] This is likely the mechanism responsible for the patient presented here.

CSF is the liquid of the subarachnoid space and provides a buoyant force that cushions and suspends the brain in the cranial vault, despite its lack of rigid support. The choroid plexus of the lateral, third, and fourth ventricles are the primary site of CSF production and after circulation throughout the central nervous system, CSF is reabsorbed by arachnoid granulations near the dural venous sinuses, spinal root sleeves, and perineural spaces. Disruption in the proper production, circulation, or reabsorption of CSF can be detrimental.^[10]

CSF hypovolemia can lead to a drop in CSF barometric pressure and ICP, resulting in significantly low and negative pressures in the thecal sac. This can result in a suction-like force that can cause progressive cerebellar tonsil descent, eventually mimicking the morphologic and symptomatic presentation of CMI. The disruption of CSF flow dynamics at the craniocervical junction in this setting can cause syrinx formation.^[3]

In this low-pressure state, the brain sinks in the cranial vault, causing traction on structures including sensory nerves, meninges, and bridging veins, contributing to a constellation of symptoms. The most common symptom of SIH is postural headache, but other symptoms can mimic those of CMI, including dizziness, clumsiness, lack of appetite, and neck pain.^[8,10] The patient presented here was difficult to diagnose because her symptoms initially mimicked CMI, and it was not evident that her headaches were postural until later in the clinical course.

If conservative treatment for CSF leak is ineffective, the next treatment is an EBP.^[11] The effectiveness of an EBP is twofold: In the short-term, it creates a tamponade and resolves symptoms, and in the long-term, the deposition of fibrin and formation of scar tissue produces a seal and eliminates the leak, allowing CSF levels to normalize.^[10]

The empirical EBP in this patient provided immediate symptomatic relief and simultaneously confirmed the diagnosis of spinal CSF leak. EBP is safe and minimally invasive, and no attempt at CSF localization is warranted in the setting of a convincing clinical picture, which can negate the necessity of invasive diagnostic techniques. This can spare resources, time, and inconvenience for both the patient and physician. Patients who have experienced spontaneous CSF leak are at greater risk to experience another, and precautions may have to be taken. Due to this, we advised our patient to diminish strenuous exercise in the future.^[11]

CONCLUSION

Chiari decompression is effective at relieving CMI symptoms with few complications. Spontaneous spinal CSF leak in a patient with a history of successfully treated CMI mimicking its recurrence is exceedingly rare. To the best of our knowledge, this is the first reported case describing tonsillar descent due to CSF leak more than a decade following decompression. This is particularly unique, given that no established long-term association exists between uncomplicated Chiari decompression and spinal CSF leak. This case suggests recognizing the potential for CSF hypotension to mimic CMI even in the setting of prior surgical decompression.