Late-onset dysphagia in a giant vertebrobasilar aneurysm: The critical role of cerebrospinal fluid in brainstem protection

INTRODUCTION

Introduction (Simplified and Integrated) Aneurysms of the vertebral artery (VA) represent <5% of all cerebral aneurysms, and vertebrobasilar junction (VBJ) aneurysms account for only 3–4% of posterior circulation aneurysms.^[1,2] Although rare, giant VBJ aneurysms are clinically significant due to their high risk of rupture and the complexity of management. When ruptured, they can lead to catastrophic hemorrhage; however, even unruptured aneurysms can cause progressive neurological deficits, especially due to brainstem compression.^[3,4]

Dysphagia is one of the key clinical signs, often resulting from compression of cranial nerves IX and X. Interestingly, symptoms may remain absent for years despite aneurysm growth. This delayed presentation is thought to be due in part to the gradual nature of aneurysm expansion, which may allow the brainstem to slowly shift and adapt. Moreover, the confined space of the posterior fossa would typically suggest early symptom onset, yet clinical signs often appear only after the aneurysm reaches a substantial size.^[5-7]

In some cases, associated hydrocephalus may further obscure symptoms, particularly those related to brainstem compression.^[8] Surgical intervention, such as ventriculoperitoneal (VP) shunting, while necessary to relieve intracranial pressure (ICP), may abruptly remove cerebrospinal fluid (CSF) buffering, resulting in sudden symptom progression.

We hypothesize that CSF dynamics, particularly the buffering effect of CSF around the brainstem play a critical role in delaying the onset of symptoms in vertebrobasilar aneurysms, and that abrupt CSF loss can unmask these symptoms.

CASE PRESENTATION

A 54-year-old male presented to the emergency department with severe headache, vomiting, gait disturbance, instability, and urinary incontinence consistent with the classic triad of Adams-Hakim syndrome. He had a history of mild vertigo for a month, with worsening headache and vomiting in the past 3 days. Neurological examination revealed a Glasgow coma scale of 15 and no focal deficits. The patient was admitted to the Neurosurgery Department of Research Education Hospital in Samsun, Türkiye in 2019.

Cranial computed tomography (CT) revealed obstructive hydrocephalus with enlarged lateral ventricles and marked periventricular edema due to fourth ventricle entrapment. Further evaluation showed a giant lesion in the posterior fossa, approximately 37 mm in diameter, compressing the brainstem and causing hydrocephalus [Figure 1]. Magnetic resonance imaging (MRI) and CT images demonstrated posterior displacement of the medulla oblongata, pons, and fourth ventricle, yet no clinical signs of brainstem or lower cranial nerve compression were noted at admission. The lesion was suspected to be a giant thrombosed vertebrobasilar aneurysm, based on its location and lack of contrast enhancement on MR angiography. T1- and T2-weighted magnetic resonance (MR) images confirmed intraluminal thrombus [Figure 2]. The aneurysm had been incidentally discovered 8 years earlier, and the patient had since been on antiplatelet therapy without intervention.

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Figure 1:

Computed tomography (CT) ımages. (a) Giant aneurysm (37 × 29 mm) at brainstem level (large arrow); posterior brainstem displacement (small arrow). (b) Hydrocephalus with periventricular edema. (c) Early post-ventriculoperitoneal shunt control CT. (d) One-month follow-up CT showing reduced ventricles and resolution of edema.

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Figure 2:

Magnetic resonance (MR) imaging findings. (a) T1 sagittal: Intraluminal thrombus in aneurysm (arrow). (b) T2 sagittal: Thrombosed aneurysm (arrow). (c) Aneurysm compressing and displacing the brainstem posteriorly (Brainstem Shift) (arrow and dotted lines). (d) Enlarged ventricles with prominent periventricular cerebrospinal fluid leakage (arrow). (e) MR angiography showing flow void (arrow); aneurysm excluded from circulation.

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Initial treatment involved medical management for brain edema, followed by VP shunt placement after 2–3 days. The patient’s hydrocephalus-related symptoms completely resolved postoperatively. One-month follow-up imaging showed decreased ventricular size and stable aneurysm dimensions. However, at the end of the first month, the patient developed progressive dysphagia, particularly with liquids, accompanied by impaired cough reflex. Although the aneurysm size remained unchanged, MR images suggested increased brainstem compression, likely due to loss of CSF buffering after VP shunting. It was concluded that the aneurysm began transmitting pulsatile forces more directly to the brainstem, leading to new-onset dysfunction of the lower cranial nerves. The clinical course of the patient is given in Table 1.

The patient’s brainstem compression symptoms gradually increased. Intervention for the aneurysm could not be performed. Aspiration pneumonia occurred due to difficulty swallowing. Therefore, he was admitted to the intensive care unit of the hospital due to severe respiratory failure. He could not overcome the pulmonary organ failure and exitus occurred after one month.

DISCUSSION

In this case, a large thrombosed vertebrobasilar aneurysm led to progressive hydrocephalus, which masked brainstem compression for nearly a decade. Dysphagia in VA and VBJ aneurysms is typically caused by direct brainstem compression, and symptom severity increases as the aneurysm enlarges. However, hydrocephalus can delay the emergence of these symptoms by creating a cushioning effect, and paradoxically, VP shunting may worsen dysphagia by removing CSF protection, thereby increasing direct aneurysm-brainstem contact.^[8-10] Only a few studies in the literature have directly addressed this phenomenon.

Brainstem shift and the protective role of CSF

This case demonstrates that hydrocephalus can initially mask brainstem compression and that sudden CSF depletion after VP shunting can accelerate the progression of dysphagia. The gradual displacement of the brainstem over several years (brainstem shift) further supports the neuroprotective role of CSF.^[5] In this patient, CSF acted as a natural cushion, allowing the brainstem to gradually adapt to the growing aneurysm without immediate compression.^[6] This displacement reduced mechanical stress on the brainstem and delayed clinical symptoms [Figure 1].

MRI findings confirmed that the brainstem had slowly shifted away from the aneurysm, protecting it from direct pulsatile forces.^[7] After CSF depletion, however, this buffer was lost, and the brainstem became exposed to unmitigated arterial pulsations, resulting in the rapid development of dysphagia.^[8] Brainstem shift is occasionally observed in cases of acute subdural hemorrhage following trauma, but such displacements are usually fatal and incompatible with life.^[11]

The pathophysiological mechanism underlying the progression of dysphagia is detailed in Table 2, and the protective role of CSF is illustrated in Figure 3.

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Figure 3:

Illustration showing (a) cerebrospinal fluid (CSF) -mediated brainstem protection and (b) direct arterial pulsation on the brainstem following CSF loss after shunting.

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Table 2: Change in clinical progression of dysphagia.

The role of aneurysm growth and CSF changes in dysphagia progression
1	Hydrocephalus as a masking factor	CSF serves as a mechanical buffer between the aneurysm and the brainstem, delaying the onset of dysphagia symptoms.
2	Brainstem shift and delayed symptoms	The brainstem had been gradually repositioning over time, supported by CSF, but once the CSF cushion was lost, neurological symptoms appeared abruptly.
3	Impact of VP shunting	The abrupt loss of CSF following VP shunting removed this protective buffer, allowing direct pulsatile forces from the aneurysm to act on the brainstem, leading to sudden dysphagia onset.

VP shunt: Ventriculoperitoneal shunt, CSF: Cerebrospinal fluid.

CONCLUSION

This case demonstrates how CSF plays a protective role in brainstem compression by vertebrobasilar aneurysms, delaying symptom onset through gradual brainstem displacement (brainstem shift). However, CSF depletion after VP shunting eliminates this protection, leading to sudden dysphagia progression. These findings highlight the need for careful CSF management to prevent abrupt neurological complications in hydrocephalus patients with posterior circulation aneurysms.

As a single-subject case report, the findings may not be generalizable; however, they underscore the need for prospective studies exploring CSF dynamics and brainstem compression in posterior circulation aneurysms.