2025 Volume 12 Pages 221-226
We report a case of syringomyelia in a 55-year-old man with a unique obstruction of Magendie's foramen. Spinal magnetic resonance imaging revealed a large syrinx extending from C1 to C3, with intermittent syringomyelia extending down to Th11. While the obstruction was not clearly evident on T2-weighted imaging, three-dimensional constructive interference in steady-state imaging demonstrated a thickened membranous tissue blocking the cerebrospinal fluid outlet, leading to syrinx formation.
Surgical intervention, involving the resection of the thickened membrane to open the foramen of Magendie, resulted in considerable improvement in the syringomyelia and neurological symptoms. Histopathological examination revealed gliomesenchymal tissue, suggesting an embryonic origin of the obstruction. This case highlights the importance of detailed imaging, particularly three-dimensional constructive interference in steady-state sequence, in diagnosing foramen of Magendie obstruction and the potential for successful surgical treatment in selected cases. Histopathological examination is crucial for differentiating gliomesenchymal tissue from adhesive arachnoiditis.
Obstruction of the cerebrospinal fluid (CSF) outlet from the fourth ventricle often leads to hydrocephalus and/or syringomyelia.1-6) Membranous anomalies around the foramen of Magendie have been associated with congenital disorders in children, such as Dandy-Walker syndrome, Arnold-Chiari malformation, and Blake's pouch cysts. In adults, such obstructions can result from adhesions due to infection, trauma, or intraventricular hemorrhage.7,8) It is well known that syringomyelia can also occur in Chiari type 1 malformation, although the underlying mechanism differs. We report an adult case of syringomyelia associated with foramen of Magendie obstruction due to abnormally thickened tissue, which is pathologically rare and of embryological interest.
A 55-year-old man with no significant medical history, trauma, or family history of neurological disorders was referred to our hospital due to the slow progression of left lower extremity paresis and sensory disturbance that began in his 30s. He had no headaches, cranial nerve symptoms, or urinary disturbances. Examination revealed mild paresis of the left lower extremity and a mildly spastic gait on the left side. The patient also reported a diffuse decrease in pain, touch, and vibration sensations on the left side, particularly below the Th10 level. All deep tendon reflexes were hyperactive, and the Babinski sign was positive in the left lower extremity.
Magnetic resonance imaging (MRI) revealed a large syrinx extending from C1 to C3, with intermittent syringomyelia extending down to Th11, along with spinal cord atrophy (Fig. 1A). A more detailed evaluation using three-dimensional constructive interference in steady-state (3D-CISS) MRI of the region around the foramen magnum showed a thickened tissue structure occupying the posterior cistern of the foramen magnum. This structure appeared to obstruct the CSF outlet by adhering to the brain tissue around the obex and occluding the foramen of Magendie (Fig. 1B). The fourth ventricle itself was not enlarged, but the inferior portion of the foramen of Magendie was enlarged (Fig. 1C), and there appeared to be a connection between the cervical syrinx and a thin central canal-like structure (Fig. 1D). The bilateral Luschka foramina appeared open (Fig. 1E), and the third and lateral ventricles were normal in size (Fig. 1F).
Preoperative MRI scans. (A) T2-weighted sagittal MRI of the spine shows a large syrinx extending from C1 to C3, with intermittent syringomyelia extending to Th11 and associated spinal cord atrophy. The obstruction of the foramen of Magendie is not clearly visualized (black arrow). Sagittal CISS MRI sequences (B and C) reveal a thickened membrane (white arrow) overlying the foramen of Magendie and inferior enlargement of the fourth ventricle. There is no evidence of aqueductal stenosis or third ventricle dilatation. Reconstructed CISS images (D) show a narrow central canal connecting the syrinx to the fourth ventricle. Axial CISS images (E) show that the foramina of Luschka are normal in size. A T2-weighted axial image of the brain (F) shows that the lateral ventricles are normal in size. CISS: constructive interference in steady-state; MRI: magnetic resonance imaging
We determined that the patient's progressive symptoms were due to syringomyelia and that opening the foramen of Magendie could be an effective treatment. Therefore, we planned surgical intervention. During surgery, the patient was placed in the prone position, and foramen magnum decompression, along with C1 laminectomy, was performed. After opening the dura mater around the foramen magnum, a thickened, complex membranous tissue was found occupying the cistern and adhering to the inferior cerebellum and dorsal cervical spinal cord (Fig. 2A and B). The membrane was carefully dissected and resected piece by piece to clear the dorsal cisterna magna. The fourth ventricle was then exposed (Fig. 2C), and the space was further enlarged to ensure adequate CSF outflow from the fourth ventricle (Fig. 2D). We confirmed that sufficient communication was established between the fourth ventricle and the dorsal cistern of the upper cervical region. Since complete removal of the membranous tissue was not feasible, the remaining lateral portions were sutured and fixed to the dura mater to prevent midline adhesion (Fig. 2D, arrowhead). For duraplasty, an artificial dura mater (Gore-Tex Surgical Membrane) was used to create additional space within the region.
Intraoperative findings. In all images, the top corresponds to the caudal direction, and the bottom corresponds to the cranial direction. (A) After dural opening, a thickened membranous structure covering the foramen of Magendie (asterisk) was identified. (B) A magnified view of the area enclosed by the dotted line. (C) The membranous structure was dissected, and the fourth ventricle was opened. The choroid plexus within the fourth ventricle is indicated by the black arrow. (D) The remaining thickened membrane was sutured to the right dura mater to prevent obstruction of the cerebrospinal fluid outflow pathway (white arrowhead).
The pathological findings are shown in Fig. 3. The excised membranous structure mainly consisted of connective tissue with interspersed glial tissue. The glial tissue was predominantly composed of astrocytes, and no neurons were observed. There was no evidence of inflammatory cell infiltration or tumor cells. Based on these findings, the excised membrane was diagnosed as gliomesenchymal tissue, composed of both neuroglial and mesenchymal components.
Photomicrographs showing histopathological features of the resected membrane. (A) Low-magnification view showing a predominant connective tissue component. (B and D) GFAP-positive glial tissue intermingled within the connective tissue. (C) Higher-magnification view demonstrating astrocytes and numerous corpora amylacea (black arrow). Neurons, inflammatory cells, and neoplastic cells were not identified. Stains used: Elastica–Goldner (A and B), H&E (C), and GFAP staining (D). Scale bars: 225 μm (A), 110 μm (B and D), and 45 μm (C). GFAP: glial fibrillary acidic protein; H&E: hematoxylin and eosin
The patient was discharged 12 days postoperatively without any complications and with some improvement in preoperative sensory symptoms. Postoperative MRI showed sufficient removal of the abnormal tissue, a widely opened foramen of Magendie in the surgical region (Fig. 4A), and a marked decrease in the syrinx (Fig. 4B). During the 5-year follow-up period, there was no symptom deterioration or recurrence on imaging. The patient's spastic gait improved to the extent that it no longer interfered with daily activities.
Postoperative MRI scans. (A) Sagittal CISS images show that the foramen of Magendie is widely opened, and the fourth ventricle has decreased in size. (B) T2-weighted sagittal MRI of the spine shows a marked reduction in the size of the syrinx. CISS: constructive interference in steady-state; MRI: magnetic resonance imaging
Syringomyelia in the present case, with a slow progression of clinical symptoms from the patient's 30s to 50s, is extremely rare. The cause was a thickened gliomesenchymal tissue mass located in the dorsal cisterna magna, which should be considered one of the congenital anomalies. Typically, syringomyelia due to pathological lesions around the foramen magnum is associated with cerebellar tonsillar herniation in patients with Chiari type 1 malformation, which can often be treated with foramen magnum decompression alone. Cases have also been reported where impaired spinal fluid outflow, due to post-inflammatory adhesive arachnoiditis, resulted in syringomyelia.9) However, to our knowledge, there have been no reports of adult-onset syringomyelia caused by congenital remnants, as seen in the present case.
The etiology of syringomyelia is complex, with no single prevailing theory. In this case, the foramina of Luschka were normal, and only the inferior end of the fourth ventricle was enlarged, with the cervical syrinx appearing to be connected through a narrow central canal. This suggests a classic communication mechanism in syringomyelia. Gardner's "water-hammer" theory offers a plausible explanation for the pathophysiology of this condition. According to this theory, partial obstruction of the fourth ventricular outlet leads to an influx of CSF into the patent central canal during systole, driven by pulsatile pressure, resulting in syrinx formation.10) In the present case, even though the foramina of Luschka were normal, complete obstruction of the foramen of Magendie by thick membranous tissue likely caused CSF pressure from the fourth ventricle to act linearly on the central canal of the cervical cord, creating a hammer-like effect. The narrowing of the foramen magnum due to the thickened membrane, combined with the formation of a large syrinx, may have created a pressure gradient between the spinal cord and cisternal CSF space.11) This mechanism, similar to that seen in Chiari malformation, likely contributed to the development of syringomyelia.
The membranous structure occupying the cisterna magna and obstructing the foramen of Magendie was composed of gliomesenchymal tissue, containing both neuroglial and dense connective tissue. The presence of neuroglial tissue suggests that this structure was likely a remnant of fetal development. During early embryogenesis, the roof of the fourth ventricle is divided into the anterior and posterior membranous areas by the primitive choroid plexus. The anterior membranous area typically develops into part of the choroid plexus, whereas the posterior membranous area forms Blake's pouch, a transient, finger-like ependymal-lined protrusion that normally regresses by the fourth month of gestation, after which the foramen of Magendie forms.12) In Chiari type 1 malformation, a thin glial membrane covering the foramen of Magendie-known as the arachnoid veil-has been observed.13,14) This structure is reported in 10%15) to 52.3%16) of Chiari I cases and is considered a risk factor for syringomyelia. Anatomical studies of 118 adult autopsy cases have shown that the size of the foramen of Magendie varies, with 3% of cases exhibiting an opening of approximately 1 mm and one case showing complete closure.17) We speculate that the gliomesenchymal tissue in this patient thickened with age and eventually obstructed the foramen, leading to the formation and progression of syringomyelia. It is presumed that the syrinx gradually expanded over an extended period, worsening with age and resulting in symptom onset in adulthood.
Treatment of foramen of Magendie obstruction depends on the underlying pathology, and a thorough imaging evaluation is crucial for selecting the appropriate surgical approach. We believe that 3D-CISS imaging is particularly valuable for detecting obstructive lesions, such as membranous structures in the ventricles or cisternal spaces.18) In the present case, 3D-CISS imaging confirmed the presence of thickened membranous tissue within the posterior cisterna magna, occluding the foramen of Magendie and impairing CSF communication between the fourth ventricle and the syrinx. This finding led us to consider whether tissue resection could improve syringomyelia. Some reports advocate placing an artificial shunt tube from the fourth ventricle to the cisterna magna as a treatment for hydrocephalus or syringomyelia caused by anatomical obstruction of the CSF outlet.5,19) However, we chose a surgical approach without shunt tube implantation, as we believed that careful MR evaluation and direct removal of the membrane alone would be sufficient to improve the condition.
Here, we report a case of syringomyelia caused by a thick membranous obstruction of the foramen of Magendie. Although rare, detailed imaging evaluation, including 3D-CISS imaging of the foramen magnum, enabled us to elucidate the underlying pathology and implement appropriate treatment. The resected membranous tissue was diagnosed as gliomesenchymal tissue, consisting of thickened fibrous and glial components, and was considered to be of embryonic origin. Accumulating additional cases and conducting further pathological examinations of similar membranous structures may contribute to a better understanding of the pathogenesis and optimal treatment strategies for syringomyelia associated with foramen of Magendie obstruction.
The authors would like to acknowledge S. Yamashita and B. Kikuchi for their support and valuable advice, and C. Tanda for technical assistance.
Informed consent was obtained from the patient involved in the study.
All authors have no conflict of interest.
