Dorsal root entry zone fenestration for intramedullary ependymal cyst: illustrative case

Shengxi Wang Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, China

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Xingang Zhao Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, China

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Tao Fan Spine Center, Sanbo Brain Hospital, Capital Medical University, Beijing, China

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BACKGROUND

Intramedullary ependymal cysts are rare and difficult to distinguish from syringomyelia and neuroenteric cysts. Almost all cases in the literature have been case reports and have been performed with the traditional posterior median sulcus incision, which is difficult to identify accurately during spinal rotation. Approximately 40% of cases have transient neurological deterioration. The dorsal root entry zone has been proven to be an effective incision area in the treatment of intramedullary lesions, but so far, its utilization in intramedullary ependymal cysts has been rarely reported.

OBSERVATIONS

This study is the first to report on six cases of intramedullary ependymal cysts treated with an 8-mm incision in the dorsal root entry zone to fully establish the communication between the cyst and the subarachnoid space. Imaging changes and neurological improvement were analyzed in all cases before and after surgery and were followed up for 49.7 months.

LESSONS

The utilization of dorsal root entry zone fenestration in intramedullary ependymal cyst has demonstrated feasibility and effectiveness, ensuring the functional integrity of the posterior column.

ABBREVIATIONS

AQP = aquaporin; DREZ = dorsal root entry zone; IONM = intraoperative neurophysiological monitoring; MEP = motor evoked potential; MRI = magnetic resonance imaging; SSEP = somatosensory evoked potential; TES = transcranial electrical stimulation

BACKGROUND

Intramedullary ependymal cysts are rare and difficult to distinguish from syringomyelia and neuroenteric cysts. Almost all cases in the literature have been case reports and have been performed with the traditional posterior median sulcus incision, which is difficult to identify accurately during spinal rotation. Approximately 40% of cases have transient neurological deterioration. The dorsal root entry zone has been proven to be an effective incision area in the treatment of intramedullary lesions, but so far, its utilization in intramedullary ependymal cysts has been rarely reported.

OBSERVATIONS

This study is the first to report on six cases of intramedullary ependymal cysts treated with an 8-mm incision in the dorsal root entry zone to fully establish the communication between the cyst and the subarachnoid space. Imaging changes and neurological improvement were analyzed in all cases before and after surgery and were followed up for 49.7 months.

LESSONS

The utilization of dorsal root entry zone fenestration in intramedullary ependymal cyst has demonstrated feasibility and effectiveness, ensuring the functional integrity of the posterior column.

ABBREVIATIONS

AQP = aquaporin; DREZ = dorsal root entry zone; IONM = intraoperative neurophysiological monitoring; MEP = motor evoked potential; MRI = magnetic resonance imaging; SSEP = somatosensory evoked potential; TES = transcranial electrical stimulation

Intramedullary ependymal cysts are rare lesions of embryonic dysplasia origin,1 accounting for approximately 0.4% of all subdural tumors.2 Only 30 cases of pathologically confirmed intramedullary ependymal cysts have been reported since 1938,2,3 mostly in the form of case reports, and their occurrence in the medullary cone is common.

The optimal surgical procedure for intramedullary ependymal cysts is controversial. The traditional surgical methods include resection, posterior median sulcus myelotomy, aspiration of cystic contents, placement of a subarachnoid shunt, biopsy, etc.1 No matter what surgical method is used, it is necessary to establish the communication between cyst and subarachnoid space. Until now, almost all literature reports have unanimously selected the posterior median spinal cord sulci to cut into the location of the cyst. However, the intramedullary ependymal cyst can grow eccentrically, the posterior median sulcus is often difficult to identify due to swelling or distortion of the spinal cord caused by the cyst,4,5 and postoperative neurological dysfunction can be as high as 40%.6 Therefore, choosing how to establish the communication between the cyst cavity and the subarachnoid space should be particularly careful.

The dorsal root entry zone (DREZ) incision technique has been proved to be a safe and effective incision area in the surgical treatment of brachial plexus avulsion pain or intramedullary lesions, such as intramedullary cavernous malformation, intramedullary ependymoma, intramedullary astrocytoma, etc. However, until now, the application of DREZ fenestration in intramedullary ependymal cysts has been rarely reported. In the current study, in cases treated between 2015 to 2022, we selected DREZ fenestration for the treatment of six patients with symptomatic intramedullary ependymal cysts, that is, an 8-mm incision was made at the DREZ. Intraoperative biopsy of the cyst wall was performed under neurophysiological monitoring, and communication between the cyst space and subarachnoid space was established.

Illustrative Case

Presentation

A 58-year-old female with a 5-year history of gradually increasing neck pain and numbness in both upper limbs was referred to our spinal treatment center. Neurological examination revealed decreased touch and pain sensation in the medial side of both upper extremities, more pronounced on the right side. Motor weakness and reflex changes were absent. Magnetic resonance imaging (MRI) of the spine showed a well-circumscribed intramedullary spindle cystic lesion at the level of the T1–2 vertebrae, approximately 12 × 9 × 26 mm in size. In the absence of contrast medium, the lesion was hypointense on T1-weighted images and hyperintense on T2-weighted images (Fig. 1).

FIG. 1
FIG. 1

A and B: Preoperative spinal MRI showing an intramedullary cyst at the T1–2 level. C: The spinal cord is filled and compressed with cysts.

Intraoperative Neurophysiological Monitoring Setup

Nicolet Endeavor CR system (Viasys Healthcare, Nicolet Biomedical) was used to monitor spinal cord function by motor evoked potentials (MEPs) and somatosensory evoked potentials (SSEPs). Neuroelectrophysiological monitoring was inhibited because of the use of muscle relaxants. The international 10/20 electroencephalography monitoring system was used to determine the installation position of SSEP monitoring electrodes at C3, C4, Cz, and FPz. Stimulating electrodes were then mounted on the surfaces of the median and posterior tibial nerves. The upper-limb N20 and lower-limb P40 waves were recorded during intraoperative SSEP monitoring. Intraoperative MEPs were monitored by transcranial electrical stimulation (TES). Two stimulating electrodes were placed at C1’ and C2’. The recording electrodes were placed on the abductor brevis muscle of the upper limb and tibialis anterior muscle of the lower limb to record the stimulus-driven compound muscle action potential.

Baseline self-control settings were performed before laminectomy. If the latency of SSEP waveform increased by more than 10% or the amplitude decreased by less than 50% and the MEP waveform disappeared or decreased during the operation, the alarm was set.

Surgical Technique

The preoperative localization was accurate. Under intraoperative neurophysiological monitoring (IONM), the T1 spinous process was exposed through the normal posterior approach and the T1 lamina was removed. The dura was opened under a microscope to reveal local distention of the spinal cord. The dorsal branch of the right nerve root was located (Fig. 2A), and an approximately 8-mm linear incision was made at the dorsal root entry zone (Fig. 2B). After fenestration, a cyst cavity filled with clear fluid was encountered (Fig. 2C and D). The cyst could not be completely removed because there was no demarcation line between the cyst cavity and the spinal cord. Therefore, part of the cyst wall was taken for biopsy examination to establish sufficient communication between the cyst and the subarachnoid space. IONM showed intact MEPs and SSEPs (Fig. 3). After tight suture of the dura, T1 lamina reduction was performed.

FIG. 2
FIG. 2

Surgical method of DREZ fenestration approach. A: The right-side of the dorsal root (black triangle) was located. B: An 8-mm linear incision was made at the DREZ. C and D: A cyst cavity (black asterisks) filled with clear fluid was encountered. E: Intraoperative nerve root position relationship, the right-side of the dorsal root (black triangle), the right-side of ventral root (hollow triangle), right lateral spinal cord (black square).

FIG. 3
FIG. 3

Intraoperative neurophysiological monitoring. Operating at the DREZ (red arrows). A: MEPs. B: SSEPs of left upper limb (blue zigzag line, left) and right upper limb (red zigzag line, right). C: SSEPs of left lower limb (blue zigzag line, left) and right lower limb (red zigzag line, right). Intraoperative baseline of self-control (green zigzag line).

Histopathological Findings

Pathology revealed a single layer of cuboidal ependymal cells lining the cyst wall, lacking a basal layer (Fig. 4). The cyst wall stained positive for glial fibrillary acid protein, S100, and cytokeratin on immunohistochemistry. There were no goblet cells or mucins, and carcinoembryonic antigen staining was negative. These results are consistent with the pathological diagnosis of ependymal cyst.3

FIG. 4
FIG. 4

Micrographs of the specimen showed a layer of cubic ependymal cells in the cyst wall, lacking a basal layer. Hematoxylin and eosin (H&E), original magnification × 200.

Postoperative Follow-up

Postoperative MRI showed that the cyst was significantly reduced, approximately 3 × 3 × 15 mm in size, and compression of the spinal cord was relieved. Postoperative neck pain disappeared, and medial numbness of both upper limbs was alleviated, but there was localized intermittent tingling in the right scapular region with a pain score of 4. The patient had no postoperative complications, and she was discharged on the sixth day after surgery. At the 1-year follow-up, spinal MRI showed no recurrence of the cyst (Supplemental Fig. 1) and no pain in the right scapular region.

Literature Review

Given the rarity of spinal ependymal cysts, we reviewed the literature (Table 1). The retrieval strategy was based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The Cochrane Handbook for Systematic Reviews of Interventions and the National Academies’ Standards for Systematic Reviews were used for reviews and electronic search strategies for peer review. We searched PubMed, Embase, the Cochrane Library, and Google Scholar using the keyword search strategy (including various spellings of “dorsal root entry zone” and “spinal ependymal cyst” or “ependymal cyst” or “intramedullary cyst”), followed by hand searching for relevant abstracts. The identified studies and relevant reference lists were examined. Titles and abstracts were screened to exclude articles that did not meet the criteria for a spinal ependymal cyst, and the full text was subsequently assessed.

TABLE 1

Summary of intramedullary ependymal cysts reported in this institution and in the literature

Authors & YearAge (yrs)/SexClinical SymptomDuration (mos)LevelSurgical Approach/Character of ContentsOutcomeFU (mos)Recurrence
Present review (2015–2022)58/F*Neck pain, bilat upper limb numbness60C7–T1DREZ fenestration/colorless transparent liquidImprove12No
44/FDizziness120C6–7DREZ fenestration/light yellow viscous cystic fluidImprove24No
55/MRt upper limb pain6C6DREZ fenestration/colorless transparent liquidImprove51No
5/FNeck pain2C1–5DREZ fenestration/colorless transparent liquidImprove54No
46/FLow back pain, paraparesis, urinary hesitancy24T10–12DREZ fenestration/colorless transparent liquidRelief74No
46/FLow back pain, rt leg weakness36T12–L1DREZ fenestration/colorless transparent liquidImprove83No
Shepard, 2017356/FLow back pain, paraparesis, urinary incontinence3T11–12Midline myelotomy+fenestrationUnchanged3No
Xie, 20141940/FBilat hand numbness6C5–7Midline myelotomy+fenestrationImprove27No
Franceschini, 20142041/FLow back pain2T11–12Midline myelotomy+fenestrationImprove24No
Yang, 2014610 casesLow back, rt leg pain, paresthesia36T11–12Midline myelotomy+fenestration; shunt, 9 cases; resection, 1 caseImprove83No
Urinary hesitancy, lt leg paresis24L1–2Unchanged75No
Urinary hesitancy, rt leg pain144T11–L1Unchanged68No
Rt leg pain6T12Improve61No
Rt leg pain, weakness12T9–10Improve59No
Rt leg pain, weakness, urinary hesitancy5L1Improve53No
Rt leg pain, weakness14T12–L1Improve48No
Lt upper limb numbness, weakness8C2Improve14No
Neck pain, lt upper, limb weakness24C6–T1Improve9No
Low back pain, lt leg pain, weakness12T8–T10Improve6No
Landi, 20141051/FBack pain, weakness, lower limbs burning paresthesiasT9Midline myelotomy+shuntImprove24No
Figueiredo, 20132148/FNeck pain, lt arm weakness4C6–T1Midline myelotomy+resectionImprove
Park, 2012946/FLt leg pain0.5T11–12Midline myelotomy+fenestrationImproveNo
Nagano, 20102264/FBilat leg pain, numbness60T11–L1Midline myelotomy+fenestrationImprove36No
Lalitha, 2006238/FPain & weakness in lower limbs0.1T2–3ResectionImprove
Saito, 20052444/FRt leg weakness12L1Linear myelotomy over dorsolat surface of cyst+shuntImprove18No
Kumar, 200174/MBilat leg weakness1T4–T6Midline myelotomyImprove5No
5/MNeck pain, quadriparesis5C1–5Midline myelotomy+fenestrationImprove4No
Iwahashi, 1999251/FBilat leg weakness1T6Midline myelotomy+fenestrationImprove18No
Robertson, 19911348/FLt leg paresthesias, weakness36T12–L1Needle+midline myelotomy+fenestrationImprove
Pagni, 1991439/MQuadriparesis6C6–7Lt paramedian myelotomyImprove18No
Sharma, 1987267/MUrinary hesitancy, lt leg weakness8T4–5Midline myelotomy+resectionImprove
Findler, 1985276/MNeck pain, bilat leg weakness1C7–T1Midline myelotomy+fenestratioImprove
Rousseau, 19832871/FBilat leg weakness108T12FenestrationImprove
Fortuna, 19782967/FLt leg weakness60T12FenestrationImprove120
57/FBilat leg weakness72T12FenestrationImprove
Hyman, 1938307/MQuadriparesis5C7–T1FenestrationImprove16

FU = follow-up.

Illustrative case.

Preliminary electronic database searches and manual retrieval identified a total of 23 articles with a total of 36 patients with spinal cord ependymal cysts. After excluding 6 cases that did not meet the inclusion criteria (2 cases were not confirmed by pathology; 4 cases of ependymal cysts were located in the extramedullary region, 3 of which were associated with schwannoma, tethered cord, lipoma or sacral cyst), 30 cases were ultimately included.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Intramedullary ependymal cysts, also known as intramedullary glial ependymal, neuroepithelial, or choroidal epithelial cysts, are rare benign fluid cysts that account for only 0.4% of spinal cord tumors.1 Given the occult nature of the disease, their true incidence may be lower. Since 1938, only 30 cases have been pathologically confirmed as single intramedullary ependymal cysts without other diseases (Table 1). Among these cases, 50% occurred in the conus, 30% in the thoracic segment, and 20% in the cervical segment. The duration of disease in females was approximately three times as long as that in the male, with an average age of 39 ± 20.32 years. The common clinical manifestations were sensory disorders and pain, followed by movement disorders and sphincter dysfunction. Intramedullary ependymal cysts do not communicate with the central spinal canal, where secretions from lining cells are absorbed or flow with the cerebrospinal fluid and do not form cysts; however, where secretions from intramedullary ependymal cysts accumulate and form cysts, their slow enlargement is considered to be the basis of progressive neurological deficits.7 Kanazawa et al.8 hypothesized that alpha-fetoprotein secretion is associated with rapid cyst enlargement. Shepard et al.3 found that cells lining intramedullary ependymal cysts express aquaporin 1 (AQP1) and aquaporin 4 (AQP4), suggesting a passive osmotic pathogenic mechanism for cyst formation.

The optimal surgical procedure for intramedullary ependymal cysts is controversial. The traditional surgical methods include resection, posterior median sulcus myelotomy, aspiration of cystic contents, placement of subarachnoid shunt, biopsy, etc.1 Regardless of the surgical method used, most patients reported improvement in postoperative symptoms, suggesting that surgical decompression is necessary. The best method is to completely remove the intramedullary ependymal cyst without damaging the spinal cord, although this is very difficult,1 and the disease has a low recurrence rate. High intramedullary pressure leads to tight adhesion of the cyst wall to the spinal cord, and total resection will lead to a deterioration of neurological function.9,10 Only a quarter of intramedullary ependymal cysts and a few extramedullary ependymal cysts can be completely removed,11 and total resection can worsen neurological damage.3,6,8,10,12 Up to now, almost all literature reports have unanimously selected the posterior median spinal cord sulcus to cut into the location of the cyst (Table 1). The intramedullary ependymal cyst grows slowly, and the location of the cyst is off-center and not communicating with the central canal, which causes the spinal cord to swell and push and rotate. When the dura is opened, the posterior median sulcus of the spinal cord cannot be identified, which will greatly affect judgment of the surgical approach.4 Although there are intraoperative neurophysiological monitoring techniques, the sensitivity of somatosensory sensation can be different because patients are under deep anesthesia. Sensory disturbance can occur after surgery, such as walking instability and an inability to completely care for oneself, which requires long-term professional neurological rehabilitation training. According to Yang et al.,6 40% of patients with intramedullary ependymal cysts experience transient neurological deterioration after surgery, with recovery of neurological function possible in approximately one-half at 1 year, but a few patients still reported no improvement. In addition, a cyst-subarachnoid shunt has also been proposed6,10,13; however, when the cyst shows thick turbidity,14,15 the silicone tube is prone to obstruction, which can also lead to spinal cord scarring and tethering.7 Therefore, the establishment of communication between the cyst cavity and the subarachnoid space should be given special attention.

DREZ fenestration is a viable option and has been proved to be a safe and effective approach for the treatment of brachial plexus avulsion pain or an intramedullary lesion (intramedullary cavernous malformation, intramedullary ependymoma, intramedullary astrocytoma, etc.). The hypothesis of DREZ fenestration is that the surgery destroys the most superficial layer of gray matter of the spinal cord neurons that are spontaneously hyperactive and associated with afferents, which are involved in processing nociceptive information. The DREZ fenestration selectively destroys the clefts I to V and Lissauer’s fasciculus (dorsolateral fasciculus), while preserving the adjacent dorsal and lateral columns. It is speculated that the destruction of the abnormally overactive area of the DREZ by myelotomy may eliminate the conduction of pain,16 and it can even achieve a pain relief rate of 85% at 2 years after surgery.17 Intraoperative nerve monitoring can significantly reduce the risk of postoperative neurological deficits.18 In this study, a total of six patients with symptomatic intramedullary ependymal cysts were treated with DREZ fenestration. Neurological function recovered after surgery, and no postoperative complications occurred. No recurrence of cysts was observed during a mean follow-up of 49.7 months.

This is the first clinical report focusing on the safe and precise treatment of intramedullary ependymal cysts by DREZ fenestration. Compared with the conventional posterior median sulcus approach, this method reduces the risk of neurological deficits associated with dorsal column injury and establishes communication between the intramedullary cyst and the subarachnoid space, effectively reducing pressure in the cyst cavity and restoring the physiological structure and function of the spinal cord. DREZ fenestration is suitable and should be considered as an option for intramedullary ependymal cyst surgery.

Observations

This study is the first to report on the treatment of 6 cases of intramedullary ependymal cysts with an 8-mm incision in the DREZ to fully establish communication between the cyst and the subarachnoid space.

Lessons

The utilization of DREZ fenestration in intramedullary ependymal cyst has demonstrated feasibility and effectiveness, ensuring the functional integrity of the posterior column.

Acknowledgments

This work was supported by the Capital Health Research and Development of Special (No. 2020-2-8011) and the Beijing Municipal Science and Technology Commission (No. Z191100006619040).

Author Contributions

Conception and design: Fan, Wang. Acquisition of data: Wang, Zhao. Analysis and interpretation of data: Wang, Zhao. Drafting the article: Wang. Critically revising the article: Fan, Wang. Reviewed submitted version of manuscript: Fan, Wang. Approved the final version of the manuscript on behalf of all authors: Fan. Statistical analysis: Wang, Zhao. Administrative/technical/material support: Wang, Zhao. Study supervision: all authors.

Supplemental Information

Online Only Content

Supplemental material is available with the online version of the article.

Supplemental Fig. 1. https://thejns.org/doi/suppl/10.3171/CASE23402.

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Supplementary Materials

  • Collapse
  • Expand
  • FIG. 1

    A and B: Preoperative spinal MRI showing an intramedullary cyst at the T1–2 level. C: The spinal cord is filled and compressed with cysts.

  • FIG. 2

    Surgical method of DREZ fenestration approach. A: The right-side of the dorsal root (black triangle) was located. B: An 8-mm linear incision was made at the DREZ. C and D: A cyst cavity (black asterisks) filled with clear fluid was encountered. E: Intraoperative nerve root position relationship, the right-side of the dorsal root (black triangle), the right-side of ventral root (hollow triangle), right lateral spinal cord (black square).

  • FIG. 3

    Intraoperative neurophysiological monitoring. Operating at the DREZ (red arrows). A: MEPs. B: SSEPs of left upper limb (blue zigzag line, left) and right upper limb (red zigzag line, right). C: SSEPs of left lower limb (blue zigzag line, left) and right lower limb (red zigzag line, right). Intraoperative baseline of self-control (green zigzag line).

  • FIG. 4

    Micrographs of the specimen showed a layer of cubic ependymal cells in the cyst wall, lacking a basal layer. Hematoxylin and eosin (H&E), original magnification × 200.

  • 1

    McNutt SE, Mrowczynski OD, Lane J, et al. Congenital spinal cysts: an update and review of the literature. World Neurosurg. 2021;145:480491.e9.

  • 2

    Fortuna A, Mercuri S. Intradural spinal cysts. Acta Neurochir (Wien). 1983;68(3–4):289314.

  • 3

    Shepard MJ, Padmanaban V, Edwards NA, Chittiboina P, Ray-Chaudhury A, Heiss JD. Discovery of aquaporin-1 and aquaporin-4 expression in an intramedullary spinal cord ependymal cyst: case report. World Neurosurg. 2017;107:1046.e11046.e7.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4

    Pagni CA, Canavero S, Vinattieri A, Forni M. Intramedullary spinal ependymal cyst: case report. Surg Neurol. 1991;35(4):325328.

  • 5

    Tsujino K, Kanemitsu T, Tsuji Y, et al. Anatomical limitation of posterior spinal myelotomy for intramedullary hemorrhage associated with ependymoma or cavernous malformation of the high cervical spine. Neurol Med Chir (Tokyo). 2022;62(6):300305.

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6

    Yang T, Wu L, Deng X, et al. Clinical characteristics and surgical outcomes of spinal intramedullary ependymal cysts. Acta Neurochir (Wien). 2014;156(2):269275.

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