2024 年 11 巻 p. 421-425
Intradural lumbar disc herniation (ILDH) is a very rare condition, with cerebrospinal fluid (CSF) leakage as a postoperative complication. The central canal of the conus medullaris was reported to communicate with the subarachnoid space through a caudal aperture; however, this aperture has never been observed in vivo. Herein, we report a case of L1/2 ILDH with postoperative spinal adhesive arachnoiditis and syringomyelia in which the communication considered to be a caudal aperture was detected. A 67-year-old woman complained of acute lower back pain and right leg pain with muscle weakness. Magnetic resonance imaging (MRI) revealed a large mass in the spinal canal at the L1/2 level. Intraoperatively, no herniated fragments were found in the epidural space. Thus, ILDH was suspected, and an intradural examination revealed tightly adherent herniated fragments in the swollen cauda equina and surrounding neovascularization. Postoperatively, symptoms improved once; however, 3 months later, severe bilateral leg muscle weakness and urinary retention developed. She was diagnosed with postoperative syringomyelia by MRI, and myelography and follow-up computed tomography was performed. Immediately after the administration of nonionic contrast agents, the syrinx of conus and epiconus were delineated through the central canal, and the communication between the central canal and the subarachnoid space could be visualized. Symptoms improved after syringo-subarachnoid shunt and duroplasty. It is likely that when CSF perfusion was impaired because of adhesive arachnoiditis around the conus medullaris, the central canal, which had been obstructed with growth, reopened, and the patient presented with syringomyelia.
Intradural lumbar disc herniation (ILDH) was first reported by Dandy et al.1) in 1942 and was reviewed by Kataoka et al.2) in 1989, who reported it as a very rare condition, accounting for 0.04%-0.33% of lumbar disc herniation cases and that L4/5 is the most common level, accounting for 50% of ILDH cases. Postoperative complications include cerebrospinal fluid (CSF) leakage and spinal arachnoidal cysts.1-4)
Several hypotheses have been proposed regarding the pathophysiology of syringomyelia; however, it is not well understood and requires further elucidation.5) Syringomyelia has various definitions related to the existence of an enlarged central canal, the lining of the cyst wall with ependymal cells, and the distinction from hydromyelia. The distinction between syringomyelia and hydromyelia has been considered less than absolute or critical, and in this report, syringomyelia was defined as an intramedullary cystic lesion.6)
The central canal begins to narrow after birth and is obstructed in 90% of adults aged >20 years and all those aged >65 years. The most severely stenotic area is between T2 and T8, and the cephalocaudal end side of the canal is relatively spared.7) The caudal portion of the central canal was communicated with the subarachnoid space through the caudal aperture; however, this has never been observed in vivo.8)
Herein, we describe a rare case of L1/2 ILDH with postoperative spinal adhesive arachnoiditis and syringomyelia with central canal enlargement. The communication between the central canal and the subarachnoid space was visualized using myelography and follow-up computed tomography (CT myelography). This communication most likely occurs through the caudal aperture.
A 67-year-old woman presented to a doctor for acute lower back pain and right leg pain and muscle weakness. Magnetic resonance imaging (MRI) showed a large low-intensity mass on T2-weighted imaging in the spinal canal at the L1/2 level (Fig. 1a-b); subsequently, she was referred to our hospital for surgery 14 days after the onset of symptoms. Physical examination revealed muscle weakness in the right iliopsoas and further distal muscles, causing walking difficulty. Bowel and bladder functions were preserved. She was initially diagnosed with lumbar disc herniation and underwent surgery 17 days after onset. Spinous process-splitting partial laminectomy and herniotomy were performed; however, herniated disc fragments were not found in the epidural space, and ILDH was suspected. Dorsal durotomy revealed that several larger disc fragments and more than a dozen smaller disc fragments firmly adhered to each swollen cauda equina. They were resected as much as possible without damaging the cauda equina. The ventral dura, which corresponds to the hernia gate, was not sutured because of its severe adhesion and excessive bleeding due to neovascular disruption during attempted resection, and the dorsal dura was closed and sealed with fibrin glue. Postoperatively, right leg muscle weakness and pain improved without complications, such as CSF leakage, and the patient could walk independently. Three months after surgery, severe muscle weakness in both legs and urinary retention progressed gradually. T2-weighted MRI showed a high-intensity lesion from the conus to the epiconus, which was not present on the preoperative images, and she was diagnosed with syringomyelia with adhesive arachnoiditis (Fig. 1c-d). On CT myelography, the central canal and syrinx of the conus and epiconus and the subarachnoid space were delineated immediately after the administration of nonionic contrast agents (Fig. 2a-d). Thus, the communication between the central canal and the subarachnoid space could be confirmed (Fig. 2d). Additional laminectomy, dissection of the arachnoid adhesion, syringo-subarachnoid shunt, and duroplasty were performed (Fig. 3). Due to the intense adhesions, the subarachnoid space was exposed by dissection from the intact area. Intraoperative ultrasound confirmed that it was definitely the syrinx and myelotomy was performed. A shunt tube 1.4 mm in diameter and 40 mm long was placed in the syrinx on one side and in the caudal ventral subarachnoid space on the other side. In addition, a drainage tube was placed to connect the cephalocaudal side of the intact subarachnoid space across the adhesion site, and duroplasty with an artificial dura mater was performed (Fig. 3). Postoperatively, her lower limb muscle weakness, and urinary retention also gradually improved. Two years after the last surgery, her muscle weakness and urinary retention completely resolved, but the MRI showed partial residual syrinx (Fig. 4a-c).
Preoperative and 3 months postoperative T2-weighted magnetic resonance imaging. (a) Sagittal and (b) axial images before surgery. (c) Sagittal and (d) axial images 3 months after surgery. A white arrow indicates syringomyelia. A white arrowhead indicates the enlargement of the central canal.
CT myelogram 3 months postoperatively. (a) Sagittal and (b-c) axial images. A white arrow indicates syringomyelia. A white arrowhead indicates the enlargement of the central canal. (d) Reconstructed CT image focused on the central canal. A white arrowhead indicates the enlargement of the central canal. A white arrow indicates the communication between the central canal and the subarachnoid space.
Intraoperative photograph. The shorter green tube implanted into the syrinx is syringo-subarachnoid shunt tube, and the longer one is the drainage tube connecting the intact subarachnoid space.
The 18-month postoperative T2-weighted magnetic resonance imaging. (a) Sagittal and (b-c) axial images. A white arrow indicates the residual syrinx.
We reported a rare case of L1/2 ILDH. To the best of our knowledge, 76 new ILDH cases have been reported since Kataoka et al.2) reported their review in 1990, with L1/2 ILDH accounting for 12%. Postoperative adhesive arachnoiditis and syringomyelia were not reported in all papers regarding L1/2 ILDH,9) and case reports including cervical and thoracic intradural disc herniation did not mention postoperative adhesive arachnoiditis and syringomyelia, indicating that this is the first report of such a rare case. Syringomyelia must be considered one of the differential diagnoses, and when neurological symptoms recur after surgery for ILDH more cranial than L2/3, MRI must be performed.
CSF was thought to be a tertiary circulation; however, a recent study reported that CSF does not flow in one direction.10) Although the pathogenesis of syringomyelia caused by adhesive arachnoiditis has not been clarified, it is believed to be caused by CSF retention in the spinal cord parenchyma resulting from the obstruction of venous return on the spinal cord surface caused by the adhesion of the subarachnoid space. In the present case, the main cause of syringomyelia and adhesive arachnoiditis was intradural inflammation caused by the surgery. It is also relevant that ILDH occurs around the medullary cone, where the spinal cord and numerous cauda equina are intermingled. In addition, the lack of closure of the hernia gate may have been a contributing factor. Previous reports on ILDH suggest that closure of the ventral dura corresponding to the hernia gate is performed in half of the cases, suggesting that closure is not always necessary. However, most cases of ILDH occur in the lower lumbar spine and not in lesions close to the spinal cord, as in the present case. The ventral dura was not repaired in this case due to its severe adhesion and excessive bleeding. Based on the course of this case, it is better to perform the repair of the ventral dura whenever possible for ILDH occurring near the spinal cord.
This is the first time that the communication between the central canal of the conus medullaris and the subarachnoid space was visualized in vivo by CT myelography. This communication most likely occurs through the caudal aperture. The central canal and subarachnoid space through the caudal aperture were accidentally possibly connected in this case, or the syringomyelia caused perforation between the central canal and subarachnoid space. However, a previous cadaver study reported that the central canal of the conus medullaris and subarachnoid space may be histologically connected through the caudal aperture.8) This aperture has been reported to be approximately 150 μm long and 130 μm wide and located at approximately 16.5 ± 5.0 mm caudally from the most cranial root of the 5th sacral nerve. Accordingly, it is possible that the central canal, which is obstructed with age, reopened by syringomyelia associated with adhesive arachnoiditis and enlargement of the central canal in the conus medullaris, detecting a communication between the central canal of the conus medullaris and the subarachnoid space through the caudal aperture in CT myelography.
To our knowledge, this is the first report of a rare case of L1/2 ILDH with postoperative spinal adhesive arachnoiditis and syringomyelia accompanied by central canal expansion. In this case, the syringomyelia was mainly caused by intradural surgical manipulation. The communication between the central canal and the subarachnoid space was visualized by CT myelography for the first time. This communication most likely occurs through the caudal aperture.
We thank Enago for the English language editing.
HH: study design, collecting clinical data, and drafting the manuscript; TY: study design, collecting clinical data, and revision of the manuscript; YM: study design and collecting clinical data; MK: study design, collecting clinical data, and critical revision of the manuscript.
The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.
The study was conducted following the Declaration of Helsinki and with the approval of the ethical review boards of our institution and Osaka University Hospital (approval no. R4-6/11360-6).
Informed consent was obtained from the patient and opt-out information was posted on the hospital's homepage.
All authors have no conflict of interest.
