Idiopathic Normal Pressure Hydrocephalus with Brain Herniation into the Arachnoid Granulation of the Lateral Lacuna of the Superior Sagittal Sinus: A Case Report

Ryusei NOBORI; Hisaaki UCHIKADO; Jin KIKUCHI; Takehiro MAKIZONO; Yosuke HASHIMOTO; Motohiro MORIOKA

doi:10.2176/jns-nmc.2025-0432

Abstract

Idiopathic normal pressure hydrocephalus is a disease of unknown cause that occurs in people aged 60 years or older and causes gait disturbance, cognitive decline, and urinary problems. A 63-year-old man with untreated diabetes presented with unsteady gait and amnesia. Head magnetic resonance imaging revealed disproportionately enlarged subarachnoid-space hydrocephalus and brain herniation into the para-superior sagittal sinus arachnoid granulation. Although the patient experienced generalized convulsions immediately before surgery, a lumbo-peritoneal shunt was performed, and symptoms improved. These brain herniations into the arachnoid granulation might accelerate the pathology, and idiopathic normal pressure hydrocephalus with brain herniation into the arachnoid granulation of the lateral lacuna of the superior sagittal sinus is extremely rare and has not been reported previously.

Introduction

Idiopathic normal pressure hydrocephalus (iNPH) is a disease that presents with gait disturbance, followed by dementia and urinary incontinence.¹⁾ iNPH occurs in people aged 65 and older.¹⁾ However, iNPH is rare in individuals younger than 65 years, and a secondary factor should be considered. We report an extremely rare case of iNPH with brain herniation into the arachnoid granulation of the lateral lacuna of the superior sagittal sinus (SSS).

Case Report

The patient was a 63-year-old male taxi driver with diabetes and cervical ossification of the posterior longitudinal ligament. He visited the hospital with complaints of gait disturbance and cognitive decline. Neurological findings showed no myelopathy but demonstrated unsteady gait and amnesia. Brain computed tomography (CT) findings showed ventricular enlargement with an increased Evans index²⁾ (31%; Figure 1A). The patient was diagnosed with iNPH, and a spinal tap test (initial pressure 160 mmH₂O) was performed, which showed improvement in symptoms. A CT scan showed calcification in the area of the right diploic vein (Figure 1B and C), and coronal sections showed disproportionately enlarged subarachnoid-space hydrocephalus (DESH)¹⁾ and brain herniation in the arachnoid granulation bilaterally without T2 WI hyperintensity of the lateral lacuna of the SSS on Magnetic resonance imaging (MRI) (Figure 1D). Although the patient was in late middle age, the diagnosis of iNPH was consistent, and the treatment plan was a lumbo-peritoneal (L-P) shunt.

Figure 1

Axial CT image showing an Evans index of 31% and ventricular enlargement (A). Coronal CT image showing a small calcified lesion (asterisk) in the LL of the right parasagittal sinus (B). Sagittal CT image showing small calcified lesions (asterisk) at the border between the right frontal and parietal lobes (C). Coronal MRI image showing DESH and brain herniation (BH); BH (yellow arrow) in both SSSs (D).

CT: computed tomography; DESH: disproportionately enlarged subarachnoid-space hydrocephalus; MRI: magnetic resonance imaging

During anesthesia induction, a seizure occurred and was controlled with anticonvulsants. The L-P shunt was performed without any complications, with the pressure set at 160 mm H₂O. Gait disturbance improved, as assessed by the timed up-and-go test, from a preoperative time of 10.77 to a postoperative time of 8.94 milliseconds. Regarding cognitive function, the patient showed no improvement in the mini-mental state examination score (21 points before and after surgery). An electroencephalogram acquired 2 days after surgery showed spike waves predominantly in the parietal lobe of the right hemisphere (Figure 2A). MRI performed 6 months after surgery showed an improvement in the Evans index (28%), and no brain herniation was observed (Figure 2B). After surgery, the patient showed improvement in gait disturbance, and epileptic seizures were controlled with medication.

Figure 2

After surgery, a spike wave was observed in the right parietal lobe during resting electroencephalogram (A). An MRI 2 years after the L-P shunt surgery showed ventricular shrinkage and disappearance of the brain herniation (BH) (B).

MRI: magnetic resonance imaging

Discussion

Observations

iNPH

Normal pressure hydrocephalus (NPH) is a reversible neurological disorder that occurs primarily in older adults and is characterized by the typical clinical triad of gait disturbances, urinary incontinence, and cognitive impairment. The pathogenesis is multifactorial, and the cause remains unknown; however, it is gradually being elucidated.³⁾ There are 2 types of NPH: secondary NPH and iNPH. It is widely believed that ventriculomegaly resulting from cerebrospinal fluid (CSF) dynamics initiates a vicious cycle of neurological damage in patients with iNPH. Pathophysiological factors of hypoperfusion, glymphatic impairment, metabolism disturbance, astrogliosis, neuroinflammation, and blood-brain barrier disruption collectively cause white and gray matter lesions, which eventually lead to various iNPH symptoms.⁴^,⁵⁾ Xiao et al.⁶⁾ reported recent advances in understanding the neurobiological mechanisms of cognitive impairment in iNPH, with a particular focus on (1) abnormal CSF dynamics, (2) dysfunction of frontostriatal and entorhinal-hippocampal circuits and the default mode network, (3) abnormal neuromodulation, and (4) the presence of amyloid-beta and tau pathologies. Additionally, in 2024, the term iNPH was changed to Hakim's disease by the International Hydrocephalus Society.⁷⁾ Hakim's disease can be classified into 7 groups, and the current case is classified as late midlife hydrocephalus, based on the patient's age.

CSF meningeal lymphatic drainage

In recent years, the concept of the glymphatic and CSF meningeal lymphatic system has become increasingly important in the context of Alzheimer's disease and other conditions, representing a future research topic for intractable neurological diseases.⁸⁾ A significant proportion of CSF absorption is thought to occur via the arachnoid granulation in the region of the SSS, especially along the parasagittal dura, where arachnoid granulations are surrounded by intradural venous channels (i.e., lateral lacunae) and contiguous diploic veins involved in CSF drainage.⁹^,¹⁰⁾ Lymphatic vessels are involved in CSF absorption.¹¹⁾ Following the recent high-profile rediscovery of meningeal lymphatic vessels located in the dura mater, there has been debate regarding the exact anatomical pathways through which CSF reaches the lymphatic system.¹²⁾ Ringstad and Eide,¹³⁾ Melin et al.,¹⁴⁾ and Ringstad and Eide¹⁵⁾ demonstrated that the parasagittal dura is not the main CSF outflow route but rather a neuroimmune interface via arachnoid granulations. Furthermore, Ko et al.¹⁶⁾ reported dynamic MRI findings of CSF transport through arachnoid granulations.

Brain herniation into the arachnoid granulation

In a study of 6,160 brain MRIs conducted by Battal et al.,¹⁷⁾ brain herniation was found in 21 cases (0.32%), of which 18 were in the dural venous sinus, and 3 were in the calvarium. Brain herniation into the arachnoid granulation frequently causes tinnitus in the transverse sinus (TS).¹⁸⁾ In a study of 68 brain herniations into arachnoid granulations in 38 patients, the most common sites were the occipital squama, TS, lateral lacunae of the SSS, and straight sinus.¹⁹⁾ Brain herniation into the arachnoid granulations is associated with brain tissue damage²⁰⁾ and can also cause conversion seizures.²¹⁾

The pathology of this case was considered NPH with DESH owing to impaired meningeal lymphatic drainage accelerated by brain herniation into the arachnoid granulation between the lateral lacunae of the SSS and the diploic vein (Figure 3).

Figure 3

Anatomical medical illustration of the case.

DM: dura mater; DV: diploic vein; LV: lateral ventricle; SAS: subarachnoid space; SC: skull calvaria

Limitations

Because this is a single case report, the involvement of glymphatic drainage or meningeal lymphatic drainage remains unclear. However, we speculate that this case report suggests that brain herniation into the arachnoid granulation in iNPH with DESH contributed to the rapid progression of symptoms.

Conclusions

Although the pathology of iNPH has not yet been fully elucidated, several complex pathological mechanisms may contribute to its development. Brain herniation into the arachnoid granulation may accelerate the pathology of iNPH, and iNPH with Brain herniation into the arachnoid granulation of the lateral lacunae of the SSS is extremely rare and has not been reported previously.

Acknowledgments

We thank Sarina Iwabuchi, PhD, from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.

Conflicts of Interest Disclosure

All authors have no conflict of interest.

Informed Consent

Informed consent was obtained from the patient.

References

責任著者(Corresponding author)

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