Brainstem auditory evoked potentials in Chiari-II malformation

Prognostic value of newborn hearing screening in patients with myelomeningocele

OBJECT

Brainstem dysfunction occurs in a minority of patients with myelomeningocele (MMC), most of whom have Chiari Type II malformation. Some surgeons advocate early identification of these patients for craniocervical decompression to avoid significant mortality. The auditory brainstem response has been found to be abnormal in most children with MMC. The present study examines whether failure of routine newborn hearing screening (NHS) predicts brainstem dysfunction in MMC patients.

METHODS

The charts of 40 newborns with MMC and 50 newborns without MMC who stayed in the neonatal intensive care unit were reviewed. Results of NHS, brainstem symptoms, birth demographics, and surgical history were retrospectively examined. Differences in the presence and onset of brainstem symptoms by NHS result were assessed.

RESULTS

Failure of NHS was more common among newborns with MMC who developed brainstem symptoms (31%, 4 of 13 patients) than among newborns without MMC (0%, 0 of 50 patients; p = 0.001). Among the 40 newborns with MMC, brainstem symptoms were more common in those who failed NHS (80%, 4 of 5 patients) than in those who passed (26%, 9 of 35 patients; p = 0.031). Respiratory symptom onset occurred later in patients who failed NHS (median 16 months) than among those who passed (median 0 months; p = 0.022). The positive and negative predictive values of NHS for brainstem dysfunction in MMC were 0.80 and 0.74, respectively.

CONCLUSIONS

Results of NHS may help predict future brainstem dysfunction in patients with MMC and may be useful to incorporate into prognostic assessment and surgical decision making.

Shunt malfunction causing acute neurological deterioration in 2 patients with previously asymptomatic Chiari malformation Type I. Report of two cases

Patients with symptomatic Chiari malformation Type I (CM-I) typically exhibit a chronic, slowly progressive disease course with evolution of symptoms. However, some authors have reported acute neurological deterioration in the setting of CM-I and acquired Chiari malformations. Although brainstem dysfunction has been documented in patients with CM-II and hydrocephalus or shunt malfunction, to the authors' knowledge only 1 report describing ventriculoperitoneal (VP) shunt malfunction causing neurological deterioration in a patient with CM-I exists. The authors report on their experience with the treatment of previously asymptomatic CM-I in 2 children who experienced quite different manifestations of acute neurological deterioration secondary to VP shunt malfunction. Presumably, VP shunt malfunction created a positive rostral pressure gradient across a stenotic foramen magnum, resulting in tetraparesis from foramen magnum syndrome in 1 patient and acute ataxia and cranial nerve deficits from syringobulbia in the other. Although urgent shunt revisions yielded partial recovery of neurological function in both patients, marked improvement occurred only after posterior fossa decompression.

Chiari I malformation presenting with hearing loss: surgical treatment and literature review

OBJECTS

Chiari I malformations can present with a number of clinical signs and symptoms.

METHODS

We present a case of an 11-year-old girl that presented with significant sensorineural hearing loss as her only Chiari-related symptom. The patient had four audiograms that all demonstrated progressive bilateral hearing loss between 10 and 30 dB. On magnetic resonance scan, the patient was found to have a Chiari I malformation. The patient had 9 mm of tonsillar herniation but no syrinx or hydrocephalus was present. On exam, the patient did not exhibit any other symptoms of her Chiari malformation or cranial nerve abnormalities other than sensorineural hearing loss. The patient underwent a suboccipital craniotomy, C1 laminectomy, and duraplasty. The patient noted a subjective improvement in hearing and an audiogram performed at 3 months postoperatively demonstrated normal hearing bilaterally.

CONCLUSIONS

Sensorineural hearing loss may be caused by Chiari I malformations. This symptom may improve following decompression.

Auditory brainstem response abnormalities and hearing loss in children with craniosynostosis

OBJECTIVES

Craniosynostosis is a devastating disorder characterized by premature closure of the cranial plates before or shortly after birth. This results in an abnormally shaped skull, face, and brain. Little is known about hearing disorders in such patients, and nothing has been published about their auditory brainstem responses. Our objective was to evaluate such patients for auditory brainstem response and hearing disorders with the long-term goal of improving patient evaluation and management.

PATIENTS AND METHODS

We evaluated the auditory brainstem responses, hearing, and brain images of children with fibroblast growth factor receptor 2 craniosynostosis (n = 11).

RESULTS

Prolongation of the auditory brainstem response I-to-III interpeak latency was a frequent characteristic of fibroblast growth factor receptor 2 craniosynostosis, occurring in 91% of our patients. Prolongation of the III-to-V interpeak latency was an occasional characteristic, occurring in 27% of our patients. Whenever the I-to-III interpeak latency was prolonged, wave II was always abnormal. Associated morbidities included sensorineural hearing loss (27%), recurrent otitis media (100%), and Arnold-Chiari malformation (27%). Cranial decompression improved the interpeak latencies of 2 children.

CONCLUSIONS

These previously undocumented auditory brainstem response abnormalities reflect abnormal neural transmission, which could cause peripheral and central auditory processing disorders. We speculate that the major pathogenic basis of the I-to-III interpeak latency and wave II abnormalities is compression of the auditory nerve as it passes through the internal auditory meatus and posterior fossa, which would explain the auditory nerve hearing loss, tinnitus, and vertigo that affect these children. Awareness of these abnormalities could lead to important advancements in the auditory and neurosurgical assessment and management of this overlooked patient group. We provide recommendations for the improved assessment and management of these patients. In particular, we recommend that auditory brainstem response diagnostics become standard clinical care for this patient group as the best way to detect auditory nerve compression.

Masseter reflex and blink reflex abnormalities in Chiari II malformation

Masseter reflex and blink reflex were evaluated in 64 patients with a myelomeningocele and Chiari II malformation. In 46 patients, no brainstem signs or symptoms were present. Brainstem dysfunction related to Chiari II malformation occurred in 18 patients. The masseter reflex was more frequently abnormal in the symptomatic than asymptomatic patients (P = 0.02). Although the blink reflex was similarly affected in the two groups of patients (P > 0.1), it was very sensitive, being abnormal in 83% of symptomatic and 65% of asymptomatic patients. Concomitant abnormality of masseter reflex and the late contralateral blink reflex component (R2c) was almost exclusively found in symptomatic patients and reached the highest significance in separating the two groups (P = 0.002).

Assessment of brainstem function in Chiari II malformation utilizing brainstem auditory evoked potentials (BAEP), blink reflex and masseter reflex

Brainstem dysfunction was evaluated in 67 patients with myelomeningocele and Chiari II malformation using brainstem auditory evoked potentials (BAEP), blink reflex (BR) and masseter reflex (MR). Signs and symptoms related to Chiari II malformation were observed in 18 patients while 49 patients had normal brainstem findings. BAEP and BR showed a higher sensitivity of brainstem involvement than MR (BAEP=1.0, BR=0.83, MR=0.50). BR, and in particular, MR were of higher accuracy (BR=0.52, MR=0.72) than BAEP (0.39) in separating patients with brainstem signs and symptoms related to Chiari II malformation. We feel that this is due to anatomic and physiologic peculiarities of the brainstem structures mediating BR and MR. Our results suggest that brainstem reflexes can support the decision of further treatment.

Audio-vestibular manifestations of Chiari malformation and outcome of surgical decompression: a case report

Sensorineural hearing loss, tinnitus, dizziness and ataxia are recognised symptoms associated with Chiari malformations but they are rarely the presenting complaints. Patients with such symptoms are frequently referred to otolaryngologists and audiological physicians. We report a case of a 13-year-old girl who presented complaining of tinnitus and impaired hearing, and was subsequently diagnosed as having a type I Chiari malformation. Pure tone audiogram showed a mild hearing impairment on the left side and the speech audiogram was normal. Auditory brain stem responses and the electronystagmography were abnormal. The patient underwent posterior fossa decompression following which her tinnitus disappeared, the hearing problem recovered and some of the abnormal electrophysiological parameters were corrected.

Brainstem auditory and visual evoked potentials in infants with myelomeningocele

Brainstem auditory evoked potentials (BAEPs) and visual evoked potentials (VEPs) were recorded in 47 infants with myelomeningocele to determine if the evoked potentials reflected the early neurological status, and if they had prognostic value as to the children's neurological outcome. The infants were tested between 1 day and 3 months of age (mean 24 days), while still in hospital after the myelomeningocele repair. Outcome was assessed at a mean of 2 years of age. Normal BAEPs were found in 41% and normal VEPs in 62% of the patients. BAEPs were abnormal in all infants studied who had symptomatic Arnold-Chiari (AC) malformation (n = 9); VEPs were abnormal in only 55% of symptomatic infants. Of the infants who did not have symptomatic AC malformation, 53% had normal BAEPs, 69% had normal VEPs. Of the patients with normal BAEPs, 81% had normal cerebral function on follow-up. Of the patients with abnormal BAEPs, 87% had central neurological abnormalities on follow-up. Of the patients with normal VEPs, 63% were normal on follow-up; of the patients with abnormal VEPs, 71% were abnormal on follow-up. Thus, the VEPs studied early in the neonatal course do not appear to be sufficiently sensitive to be valuable prognostically in these infants. However, the BAEPs were consistently abnormal in symptomatic AC malformation and showed a positive predictive value of 88% and an accuracy in predicting central neurological sequelae of 84%.

BAEPs in infants with myelomeningocele and later development of Chiari II malformation-related brainstem dysfunction

Thirty-seven infants with myelomeningocele received brainstem auditory evoked potentials (BAEPs) at a median age of eight days. No infant had brainstem dysfunction at the time of testing. Median follow-up was at 30 months. Of 12 infants who subsequently developed brainstem dysfunction at a median age of three months, 11 had had abnormal neonatal BAEPs. In contrast, only 10 of 25 infants who did not develop brainstem dysfunction had abnormal BAEPs. The mean average I-V interpeak latencies was greater among those who developed symptoms than among those who did not. Neonatal BAEPs can identify a group of asymptomatic infants with myelomeningocele who need close follow-up for the subsequent development of brainstem dysfunction.

Evoked potentials in infant brainstem syndrome associated with Arnold-Chiari malformation

This study evaluated the contribution of brainstem auditory evoked potentials (BAEPs) and median nerve somatosensory evoked potentials (SEPs) to the assessment of brainstem dysfunction in infants with myelomeningocele and Arnold-Chiari malformation. 16 infants under one year of age were studied. Six had infant brainstem syndrome (IBS). 11 had abnormally prolonged I-V interwave latency (brainstem transmission time, BSTT); BSTT did not differentiate those patients with and without IBS. The cortical 'N20' component of the median-nerve SEPs was absent or had low amplitude and prolonged latency in all six patients with clinical signs of brainstem dysfunction and in four without. Median-nerve SEPs were normal in the patients without IBS. There was a significant difference between patients with and without IBS. Median-nerve SEPs may be a helpful measure of brainstem function in infants with Arnold-Chiari malformation.

Brain stem auditory-evoked potentials in meningomyelocele. Natural history of Chiari II malformations

Brain stem auditory-evoked potentials (BAEPs) were recorded in 30 patients with meningomyelocele and shunted hydrocephalus ranging in age from birth to 33 years. Twenty-two of them had Chiari II malformation, one of which was symptomatic. In 22 cases, including 15 with Chiari II malformation, BAEPs were recorded repeatedly after periods ranging from 18 months to 7 years. The results were as follows: (1) III-V interpeak latency (IPL) decreased progressively from prolonged to the normal range with growth until 25 years of age; (2) I-III IPL tended to prolong gradually from the normal range; (3) these findings may indicate that the natural history of Chiari II malformation is delayed maturation of the brain stem and intensification in the elongation and stretching of the hindbrain and lower cranial nerves.

Abnormal control of ventilation in adolescents with myelodysplasia

Infants with myelomeningocele have abnormalities in ventilatory control. To determine whether these persist into later life, we studied 14 patients with myelomeningocele and Arnold-Chiari malformation (age 18.0 +/- 0.8 (SE) years), and compared them with 14 control subjects (age 24.0 +/- 0.9 years). Pulmonary function and ventilatory muscle strength did not differ between patients with myelomeningocele and control subjects. Hypercapnic ventilatory responses were significantly lower in the group with myelomeningocele (1.98 L/min/mm Hg) compared with control values (3.33 L/min/mm Hg; p less than 0.01). Hypoxic ventilatory responses (-1.4 L/min/%oxygen saturation of hemoglobin in arterial blood) were not significantly different from control values (-2.14 L/min/%oxygen saturation). In control subjects the hypercapnic and hypoxic ventilatory responses were highly correlated with each other within subjects (r = 0.84; p less than 0.002) but not in those with myelomeningocele (r = 0.34; not significant). We concluded that adolescents and young adults with myelomeningocele have abnormalities in control of ventilation during sleep and wakefulness. We speculate that the Arnold-Chiari malformation interferes with central chemosensitivity (hypercapnic ventilatory response) and central integration of chemoreceptor output.