Background

Wernekinck syndrome, sometimes called superior cerebellar peduncle decussation syndrome, results from a lesion at the midline crossing of the superior cerebellar peduncles in the caudal midbrain. This rare syndrome classically produces bilateral cerebellar ataxia, with a prominent disturbance of gait and truncal stability, often accompanied by dysarthria. Most documented cases arise from focal vascular events, demyelinating plaques, or neoplastic infiltration. However, structural distortion of the midbrain from external forces can also produce this clinical picture, and an expanding body of case literature describes brainstem compression syndromes related to low cerebrospinal fluid pressure.

Case Presentation

A 34-year-old woman with a known history of joint hypermobility and chronic musculoskeletal pain presented with a three-week history of severe orthostatic headaches. The headaches reliably worsened within two minutes of standing and resolved completely with recumbency. Alongside the headache, she reported a positional hearing loss, describing a feeling of aural fullness and a distinct reduction in auditory sensitivity when upright, with normal hearing when lying flat. Audiometric assessment confirmed a low-frequency sensorineural pattern that reversed on assuming a supine posture.

Over the following days, she developed progressive unsteadiness. Neurological evaluation revealed a wide-based gait, difficulty performing tandem gait, and bilateral dysmetria on finger-to-nose and heel-to-shin testing. Speech was mildly scanning, and saccadic eye movements showed impaired smooth pursuit. There were no long-tract signs, cranial nerve deficits other than the auditory complaint, or cognitive changes. The combination of bilateral cerebellar signs in an acute-on-subacute setting raised suspicion for a midline midbrain lesion, and the clinical picture was consistent with Wernekinck syndrome.

Imaging and Diagnostic Findings

Magnetic resonance imaging of the brain demonstrated features of intracranial hypotension, including diffuse pachymeningeal enhancement, sagging of the optic chiasm, effacement of the prepontine cistern, and downward descent of the cerebellar tonsils. In addition, coronal heavily T2-weighted imaging showed abnormal hyperintensity at the level of the inferior colliculus, with visible distortion of the superior cerebellar peduncle decussation, correlating with the patient's bilateral cerebellar signs.

Because the patient was hypermobile and had no history of a dural puncture, a search for a spontaneous spinal CSF leak was undertaken. Magnetic resonance myelography revealed a focal paraspinal fluid collection in the upper thoracic region, and subsequent digital subtraction myelography identified a cerebrospinal fluid-venous fistula at the right T4 nerve root sleeve. This abnormal communication between the subarachnoid space and an epidural vein was considered the primary source of the cerebrospinal fluid leak, a finding increasingly recognised in the hypermobile patient population.

Treatment and Rebound Intracranial Hypertension

The patient underwent surgical ligation of the CSF-venous fistula. Within 48 hours, her orthostatic headaches and positional hearing loss resolved, and her gait began to improve. However, on the third postoperative day, she developed a new, constant, non-positional headache accompanied by nausea and blurred vision. Fundoscopic examination revealed bilateral papilledema, and lumbar puncture demonstrated an opening pressure of 32 cm H₂O, confirming the diagnosis of rebound intracranial hypertension.

This complication is well recognised following surgical correction of a chronic spinal CSF leak. The patient was treated with acetazolamide, and her symptoms gradually settled over several weeks. The cerebellar ataxia improved in parallel, and repeat imaging showed complete resolution of the midbrain distortion and reconstitution of the superior cerebellar peduncle decussation. At three-month follow-up, neurological examination was entirely normal apart from mild residual gait hesitancy.

Discussion

This case illustrates that Wernekinck syndrome can be a manifestation of reversible mechanical distortion of the midbrain in patients with spontaneous intracranial hypotension. The mechanism likely involves downward brain sagging with compression of the dorsal midbrain against the tentorial edge, producing focal ischaemia or direct mechanical dysfunction of the decussating cerebellar outflow fibres.

• CSF-leak: Chronic spinal CSF leak caused by a CSF-venous fistula was the underlying trigger in this case.
• Hypermobile: Joint hypermobility is a recognised risk factor for spontaneous CSF leaks and CSF-venous fistulas, and this patient's connective tissue laxity likely contributed to the formation of the abnormal fistula.
• Positional hearing loss: This unusual otologic symptom is an underrecognised feature of intracranial hypotension, attributed to altered intralabyrinthine fluid pressure that shifts with posture.
• Case: This report adds to the small literature on brainstem syndromes arising from low CSF pressure and demonstrates the value of recognising a surgically correctable cause.
• CSF-venous fistula: These fistulas are increasingly diagnosed with advanced myelographic techniques and should be considered in hypermobile patients with spontaneous intracranial hypotension and no preceding dural puncture.
• Rebound intracranial hypertension: Clinicians must monitor for this complication after fistula repair, as rapid restoration of CSF volume can overwhelm the brain's autoregulatory capacity.

Key clinical takeaways are the importance of a postural history in any patient presenting with ataxia and hearing disturbance, the need for dedicated imaging of the spinal CSF spaces when intracranial hypotension is suspected, and the possibility that a midbrain syndrome with bilateral cerebellar signs may be fully reversible when the underlying leak is repaired and rebound intracranial hypertension is managed appropriately.