2026 年 13 巻 p. 167-174
Chiari malformation type I is a structural anomaly of the posterior fossa characterized by cerebellar tonsillar herniation through the foramen magnum, often associated with disrupted cerebrospinal fluid dynamics and elevated intracranial pressure. Papilledema is a rare ophthalmic manifestation in Chiari malformation type I, typically linked to increased intracranial pressure. Isolated visual symptoms without signs of intracranial pressure in pediatric Chiari malformation type I are particularly rare and poorly understood. We report a rare pediatric case of Chiari malformation type I in a 9-year-old girl presenting solely with bilateral papilledema and visual impairment, without typical symptoms of raised intracranial pressure such as headache. Magnetic resonance imaging revealed cerebellar tonsillar descent and cervical syringomyelia. Due to progressive visual decline and the absence of alternative diagnoses, the patient underwent foramen magnum decompression with C1 laminectomy. Postoperatively, visual acuity significantly improved, although papilledema persisted at 9 months. This case challenges the conventional view that papilledema in Chiari malformation type I is solely caused by elevated intracranial pressure. Alternative mechanisms, such as localized venous congestion, mechanical stress on the optic nerve, or regional cerebrospinal fluid flow disturbances, may contribute to papilledema. Persistent papilledema despite clinical improvement supports the hypothesis of localized rather than global intracranial pressure elevation. Pediatric presentations may differ from adult cases in symptomatology and pathophysiology, requiring careful diagnostic and therapeutic considerations. Surgical decompression may lead to functional visual recovery even if anatomical signs such as papilledema persist. This case underscores the need for further research into atypical presentations and underlying mechanisms of Chiari malformation type I, especially in pediatric populations.
Chiari malformation type I (CM-I) is a congenital or acquired structural anomaly of the posterior fossa, defined by the downward displacement of the cerebellar tonsils through the foramen magnum by at least 5 mm.1) This downward displacement disrupts cerebrospinal fluid (CSF) circulation and can lead to various neurological symptoms.2) The most commonly reported symptoms are headaches and posterior neck pain, exacerbated by physical exertion, Valsalva maneuvers, head dependency, and sudden changes in posture, and are attributed primarily to elevated intracranial pressure (ICP) due to impaired CSF circulation. Nystagmus, dizziness, and ataxia are also seen in patients with CM-I.3) In addition, approximately 40% of CM-I cases are associated with syringomyelia due to disturbances in CSF dynamics, which commonly result in sensory disturbances and motor deficits.4)
Ophthalmic manifestations in CM-I are relatively frequent, including nystagmus and diplopia due to cranial nerve VI palsy.5) However, visual impairment is uncommon, observed in approximately 9% of patients with CM-I.3) Papilledema is characterized by swelling and elevation of the optic disc with blurred margins due to nerve fiber edema. It occurs in only 2.5% of patients with CM-I.3) Generally, papilledema is associated with conditions causing increased ICP, such as idiopathic intracranial hypertension (IIH) or space-occupying lesions.6) Intracranial hypertension is generally defined as a sustained elevation of ICP above the normal upper limit, typically exceeding 20-25 mmHg in adults, whereas in children, normal ICP values vary with age. In clinical practice, evidence of elevated ICP is usually based on clinical and radiological findings.7) In the context of CM-I, papilledema is also thought to result secondarily from increased ICP caused by obstructed CSF flow at the craniocervical junction.5,6) Consequently, papilledema typically coexists with other ICP-related symptoms, such as headaches.
Most symptomatic cases of CM-I occur in adults, and the applicability of findings to pediatric patients remains uncertain. For instance, a recent patient-level meta-analysis by Pando et al.8) examined 27 cases of CM-I or CM-1.5 with papilledema, but only 5 patients were under 18 years of age, limiting pathophysiological insights into the pediatric group. Moreover, among these pediatric cases, isolated visual symptoms without signs of intracranial hypertension, such as headache, were extremely rare. This scarcity of data indicates that the understanding of the unique neurovascular anatomy and CSF dynamics in pediatric patients remains limited. Here, we present a rare pediatric case of CM-I initially diagnosed based solely on bilateral papilledema and visual impairment, without typical symptoms of elevated ICP. Given the limited literature on pediatric presentations, this case offers important insights into alternative pathophysiological mechanisms and clinical decision-making in children. We describe the diagnostic process, imaging findings, surgical intervention, and postoperative course in detail. This case highlights the importance of recognizing atypical presentations of CM-I and suggests the possibility of alternative pathophysiological mechanisms that may produce papilledema independently of ICP elevation.
A 9-year-old girl was referred to our hospital following the detection of decreased visual acuity during a routine school health examination. The child had no significant past medical history or prior medication use. She had no headaches, dizziness, or other neurological complaints at the time of presentation.
Ophthalmological examinationAn initial ophthalmological assessment at a local clinic revealed bilateral papilledema, prompting referral to our institution for further evaluation. On examination, the patient's uncorrected visual acuity was 0.13 bilaterally. After correction, the best corrected visual acuity (BCVA) slightly improved to 0.16. The critical flicker fusion frequency was preserved at 38 Hz in both eyes. Although dynamic visual field testing revealed concentric constriction, the responses varied between tests and showed poor reproducibility. Intraocular pressure was within the normal range. In fundoscopic examination (Figure 1A and B), the redness around the optic disc was mild, and no retinal hemorrhage was observed; however, mild venous engorgement was suspected. Optical coherence tomography (OCT) demonstrated slight thickening around the optic disc, suggesting papilledema (Figure 2A and B). Visual evoked potentials (VEPs) showed prolonged latency in both eyes. Based on the results of the critical flicker fusion frequency and visual field testing, psychogenic visual loss was considered a possible cause of the decreased visual acuity, bringing pseudopapilledema into the differential diagnosis. However, fundus autofluorescence and ocular ultrasonography were negative for optic disc drusen.
The funduscopy findings before surgery (A, B), at 1 month after surgery (C, D), and at 9 months after surgery (E, F). A, C, and E: right eye; B, D, and F: left eye. All images show papilledema.
The OCT scan before surgery (A, B), at 1 week after surgery (C, D), and at 6 months after surgery (E, F). The TSNIT graph of the left and right sides (G, H). A, C, E, and G: right eye; B, D, F, and H: left eye. The retinal fiber layer thickness was temporarily improved after surgery, but the thickness at 6 months after surgery returned to almost the same level as before surgery.
OCT: optical coherence tomography, TSNIT graph: Temporal-superior-nasal-inferior-temporal graph
Magnetic resonance imaging (MRI) of the brain, performed to rule out structural abnormalities, showed no evidence of hydrocephalus or other lesions. No narrowing of the subarachnoid space was observed around the optic nerve or the brainstem (Figure 3A and B). However, the cerebellar tonsils were observed to extend 10 mm below the foramen magnum, consistent with a diagnosis of CM-I (Figure 3C). Syringomyelia was also noted in the cervical spinal cord. Preoperative evaluation of the venous system was performed using contrast-enhanced computed tomography (Figure 3D). The transverse, sigmoid, and straight sinuses were of normal caliber, without evidence of stenosis, hypoplasia, or filling defects. The torcular Herophili was not low-lying, and no anomalous occipital sinus or other collateral drainage pathways were identified. These findings suggested no apparent major venous stenosis or occlusion. There was also no evidence of abnormal development of the straight sinus that would contraindicate dura mater incision and duraplasty. Neurological examination at the first visit of our neurosurgery department revealed no focal deficits, and there were no signs of increased ICP, such as headache or vomiting.
MRI at the first visit to our hospital. Axial slices (A) and sagittal slices (B) of the head MRI do not show hydrocephalus or intracranial space-occupying lesions. Sagittal slices of the cervical spine (C) show herniation of the cerebellar tonsils and syringomyelia.
The 3D reconstruction of the contrast-enhanced CT scan (D) shows no venous anomaly. Arrows indicate the sigmoid sinus; arrowheads indicate the transverse sinus; the area outlined by the dashed line represents an underdeveloped occipital sinus.
3D: 3-dimensional; CT: computed tomography; MRI: magnetic resonance imaging
The clinical course was atypical for CM-I, necessitating a cautious approach in determining the surgical indication. However, given the absence of alternative causes for the papilledema and the progressive visual decline, surgical intervention was considered appropriate. After a thorough discussion with the patient and her family, surgery was performed. The patient underwent foramen magnum decompression with C1 laminectomy (Figure 4A and B). Based on preoperative venous drainage information, the dura mater was incised in a Y-shaped fashion, followed by duraplasty. The procedure lasted 211 minutes, with a total blood loss of 33 mL.
CT scan (A, B) after surgery. The axial slice at the occipital bone level (A) and the axial slice at the C1 level (B) show sufficient decompression of the posterior cranial fossa. The sagittal slice of the MRI scan of the cervical spine (at 6 months after surgery) (C) shows improvement of cerebellar tonsil herniation and syringomyelia.
CT: computed tomography; MRI: magnetic resonance imaging
The patient's visual symptoms improved significantly. By postoperative day 14, she was discharged home with improved BCVA of 1.0 bilaterally. At the 6-month follow-up, MRI showed improvement in the cerebellar tonsil herniation and syringomyelia (Figure 4C). Her BCVA remained stable at 1.0 in both eyes. Although her VEP latency showed improvement, OCT and fundus examination showed only slight improvement in the thickness of the retinal nerve fiber layer and venous engorgement immediately after surgery (Figures 1C and D and 2C and D). Although the patient's visual symptoms had resolved, OCT at 6 months postoperatively demonstrated no additional reduction in the retinal nerve fiber layer thickness, and fundus examination at 9 months postoperatively still showed persistent optic disc swelling (Figures 1E and F and 2E and F).
CM-I is a congenital or acquired anomaly of the posterior fossa, defined by the herniation of the cerebellar tonsils through the foramen magnum. Symptomatic CM-I is diagnosed in approximately 1 in every 1,000 to 1,280 individuals.9-11) Many cases, however, are incidentally discovered during MRI screenings. The actual prevalence, including pediatric cases, may be as high as 1%.9,10) This structural abnormality disrupts CSF flow dynamics and can lead to various neurological manifestations. Headache is the most common neurological symptom. Ophthalmic manifestations, such as nystagmus, are also relatively frequent.3) However, papilledema is uncommon among ophthalmologic manifestations in patients with CM-I and is generally considered to result from increased ICP due to impaired CSF flow at the foramen magnum.6) Importantly, before surgery, the patient and her parents were fully informed about the atypical clinical presentation and the possibility that visual symptoms and papilledema might not improve postoperatively. Nevertheless, her visual acuity was severely impaired, and because no effective alternative treatments were available, surgery was considered the most appropriate option.
Pediatric cases of CM-I with papilledema may differ pathophysiologically and clinically from adult cases. Furthermore, pediatric patients may underreport or fail to recognize symptoms such as headache and functional vision loss, which complicates the clinical assessment.12,13) In prepubertal patients, the relative elasticity of the skull, with partially open sutures and fontanelles, may allow some buffering of raised ICP and help to maintain venous outflow, thereby modifying the clinical expression of papilledema. Furthermore, anatomical abnormalities of the dural venous sinuses can elevate venous pressure, impair CSF absorption, and contribute to intracranial hypertension even in the absence of typical symptoms.14) Fischer et al.15) demonstrated clear age-dependent differences in both the frequency and etiology of papilledema: among patients ≤5 years, 6-12 years, and ≥13 years, those ≥13 years accounted for nearly 70% of all cases, whereas children ≤5 years represented less than 10%; in addition, papilledema in children ≤5 years was almost exclusively trauma-related, venous outflow abnormalities were the most frequent cause in those aged 6-12 years, and IIH predominated in adolescents and adults. Our 9-year-old patient, therefore, falls into the 6-12-year age group in which venous outflow disturbances are particularly relevant, and in this case, serial OCT and fundus examinations provided objective documentation of optic disc edema and venous engorgement, supporting a hemodynamic contribution to the papilledema despite the absence of headache or other signs of intracranial hypertension.
This case illustrates an uncommon pediatric presentation of CM-I, characterized by bilateral papilledema and visual impairment without signs of intracranial hypertension such as headache or vomiting. Papilledema is usually regarded as a hallmark of elevated ICP and is most often discussed in the context of IIH, space-occupying lesions, and cerebral venous sinus thrombosis. Nonetheless, the relationship between ICP and optic disc swelling is more complex than a simple linear association. Papilledema can occasionally be observed even when lumbar opening pressure is within or only mildly above the conventionally normal range, presumably because of impaired CSF absorption or regional compartmentalization of CSF spaces.16) Conversely, patients with transverse sinus stenosis-associated IIH may have markedly elevated ICP without papilledema.17) This finding highlights the imperfect coupling between global ICP and optic disc swelling.18) These observations indicate that the absence of clinical signs of intracranial hypertension does not necessarily exclude clinically meaningful pressure or flow disturbances along the visual pathway.
Venous outflow impairment represents one of the plausible contributors to such discordance. Traditionally, papilledema has been regarded as a manifestation of sustained elevation of ICP, and impaired venous outflow―such as that caused by venous sinus thrombosis or jugular vein compression―is considered to induce papilledema primarily through an overall rise in ICP.19,20) In these conditions, papilledema has almost always been accompanied by elevated ICP. However, papilledema attributable to venous outflow obstruction without radiological evidence of raised ICP has been reported in conditions other than CM-I. Diskin et al.21) described a patient receiving hemodialysis with brachiocephalic vein thrombosis causing retrograde jugular-cavernous sinus reflux and optic disc edema despite an unremarkable head computed tomography scan with no evidence of increased ICP. Similarly, Eames et al.22) reported papilledema associated with brachiocephalic vein stenosis and dialysis fistula-related jugular reflux that resolved after venoplasty and stenting. Notably, venous sinus stenosis on imaging does not necessarily parallel global ICP; Bono et al.23) reported that transverse sinus stenosis persisted on magnetic resonance venography even after normalization of CSF pressure in IIH. In CM-I, previous studies have suggested that compression or obstruction of venous structures at the craniocervical junction, particularly the sigmoid sinus or transverse sinus, may lead to impaired venous drainage, resulting in increased venous pressure within the optic nerve sheath.24) Since direct measurement of perioptic subarachnoid pressure in vivo remains difficult, a compartmentalized increase in venous pressure around the optic nerve driven by venous congestion may provide a reasonable explanation for the present findings in this case.
Another potential mechanism involves direct and hemodynamic mechanical stress on the optic nerve or its blood supply. Downward displacement of the cerebellar tonsils can distort the brainstem and posterior circulation and dynamically obstruct CSF flow at the foramen magnum, acting as a "piston" that intermittently impedes CSF outflow and generates transient pressure gradients between the cranial and spinal compartments.25) These alterations in CSF dynamics may produce a local increase in CSF pressure within the perioptic subarachnoid space and compromise perioptic and ciliary circulations, leading to chronic axonal ischemia and impaired axoplasmic transport.26,27) Consistent with this concept, previous reports have shown that papilledema can occur despite normal ICP measurements when CSF absorption is impaired due to markedly elevated CSF protein, as reported in neurofibromatosis type 2-related schwannomatosis, or when pressure transmission is regionally compartmentalized.28,29) In contrast, some patients with clearly elevated ICP do not develop papilledema because pressure is not efficiently transmitted to the optic nerve head.30) Collectively, these observations support the concept that regional CSF dynamics and compartmentalization, rather than uniform elevation of global ICP alone, are critical determinants of whether papilledema develops.
Regarding papilledema in CM-I, there have been a few reports in the previous literature. The recent meta-analysis by Pando et al.8) systematically reviewed 27 cases of CM-I or CM-1.5 presenting with papilledema and highlighted notable variability in treatment responses. Among patients who underwent foramen magnum decompression, those who had received prior medical therapy―most frequently acetazolamide―showed better postoperative outcomes.8) They suggested that medical therapy may influence postoperative outcomes. However, these drugs were primarily used in patients presenting with signs of elevated ICP. In contrast, the efficacy of these treatments in patients without overt ICP-related symptoms remains uncertain. Our case, in which papilledema developed in the absence of headache, nausea, or vomiting, raises doubts as to whether ICP-lowering interventions such as acetazolamide would have had a therapeutic benefit. Thus, while the data from Pando et al.8) suggest the utility of a stepwise approach in typical IIH-like presentations, their applicability to papilledema without clinical signs of elevated ICP, especially in pediatric CM-I, remains unproven. In this case, only surgical intervention led to significant visual improvement, but papilledema persisted at 9 months postoperatively. Vaphiades et al.31) reported that papilledema was nearly resolved in half of the 4 cases of CM-I, despite full recovery of clinical symptoms.
This single-case report has conceptual limitations regarding the interpretation of the pathophysiology. The mechanisms linking Chiari malformation, CSF dynamics, venous outflow disturbance, and papilledema are inferred from indirect clinical and imaging findings in a single patient and from hypotheses proposed in previous case reports, without direct hemodynamic or ICP measurements. These mechanisms should therefore be regarded as plausible yet still speculative rather than definitive explanations of the disease process in this child. Further studies are needed to elucidate the underlying mechanisms and optimize treatment strategies for patients with CM-I presenting with atypical ophthalmologic findings.
This case illustrates a rare presentation of pediatric CM-I, characterized solely by bilateral papilledema and visual impairment, without clinical signs of elevated ICP. Despite initial diagnostic uncertainty―including the possibilities of pseudopapilledema or psychogenic visual disturbances―the presence of objective abnormalities in VEPs supported the decision for surgical intervention, leading to postoperative symptom improvement. This case highlights the diagnostic challenges associated with isolated visual symptoms in pediatric CM-I without evidence of elevated ICP and the potential benefit of surgical treatment. Further research is needed to clarify the pathophysiology of such atypical presentations and to guide effective management strategies.
Author Ryuta Saito is a member of the Editorial Board of this journal. He was not involved in the peer-review process or in any editorial decisions regarding this manuscript. The review process was conducted independently to ensure fairness and objectivity.
This manuscript underwent English language corrections using ChatGPT (GPT-4o version). All data interpretation and final manuscript revisions were conducted by the human authors.
All authors have no conflict of interest.
Informed consent was obtained from the patient's parents.
