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Lindsay YoungUT Southwestern Medical CenterEmail: lyoun2@parknet.pmh.org

Objectives: 1. Describe the imaging findings of the membranous labyrinth, facial nerve, and cochleovestibular nerve in patients with pontine tegmental cap dysplasia (PTCD). 2. Correlate the imaging findings and the potential for successful cochlear implantation.

Methods: A retrospective case series at a tertiary care pediatric hospital was performed. Three patients were identified with PTCD. High-resolution CT and MR scans were reviewed by a pediatric neuroradiologist. Variables evaluated included radiographic findings typical of PTCD, the presence and course of cranial nerves, the appearance of the cochlea and vestibule, the size of the IAC and the presence of a duplicated IAC. Clinical data was reviewed.

Results: All patients demonstrated characteristic brain MRI findings of PTCD. Mild, bilateral cochlea dysplasia was noted in two patients and all patients had a normal vestibular labyrinth. The cochleovestibular nerves were absent bilaterally in all patients. The facial nerves were subjectively small bilaterally in one patient, unilaterally in the second patient, and normal in the third. Bilateral accessory canals for the seventh cranial nerve were present in all patients (duplicated IAC). ABR testing revealed profound bilateral sensorineural hearing loss in all the patients. No patient had facial weakness. One patient was implanted with bilateral cochlear implants and had minimal response to sound-field audiometry at one-year follow-up.

Conclusions: Bilateral profound hearing loss in patients with PTCD appears to be the result of absence of the cochleovestibular nerve. The entity should be recognized and prognosis for successful cochlear implantation is poor.

Imaging of 7th and 8th Cranial Nerve Anomalies in Pontine Tegmental Cap DysplasiaLindsay Young, MD1, Tim Booth, MD2, Peter S. Roland, MD1, J. Walter Kutz, Jr., MD1,Mario Miranda, MD3

1Department Of Otolaryngology, UT Southwestern Medical Center, 2 Pediatric Neuroradiology, UT Southwestern Medical Center, Dallas, Texas 3Radiology Division, Department of Medicine, School of Medicine, University of Panama

A retrospective case series at a tertiary care pediatric hospital was performed. Three patients were identified with PTCD. High-resolution CT and MR scans were reviewed by a pediatric neuroradiologist. Variables evaluated included radiographic findings typical of PTCD, the presence and course of cranial nerves, the appearance of the cochlea and vestibule, the size of the IAC and the presence of a duplicated IAC. Clinical data was reviewed.

PTCD is a newly discovered brain malformation with only 15 casespreviously reported in the literature. In our series, all three patients had an absent cochleovestibular nerve by MR imaging. In addition, mild cochlear dysplasia was seen in 2 patients. An accessory canal (or duplicated IAC) for the facial nerve was present in all patients, though the nerve was deficient at least on one side in 2 patients. The exit of the facial nerve from the brainstem was noted to be more superior and posterior than normal. Clinical findings were variable; however, all patients had profound SNHL None of our patients had facial paralysis; however, some of the cases reported in the literature do have a facial palsy.

Patient 3, was implanted with bilateral cochlear implantation. At one year follow up, she had minimal benefit.

Children with PTCD have consistent MR imaging findings, including absent 8th cranial nerves, duplicated IACs and aberrant position of the 7th cranial nerves. Further case series will help delineate whether our findings are universal among patients with PTCD. The duplicated IAC is a rare anomaly also found in patients without PTCD; this may provide clues in the pathogenesis of this disorder. Due to the absent 8th nerve, cochlear implantation is unlikely to be successful.

INTRODUCTION

1. Barth, P., et al. Pontine tegmental cap dysplasia: a novel brain malformation with a defect in axonal guidance. Brain 2007; 130: 2258-2266.

2. Jissendi-Tchofo, P., et al. Pontine tegmental cap dysplasia: MR Imaging and diffusion tensor imaging features of impaired axonal navigation. American Journal of Neuroradiology 2009; 30: 113-19.

3. Rauscher, C., et al. Pontine tegmental cap dysplasia: the severe end of the clinical spectrum. Neuropediatrics 2009: 40; 43-46.

4. Macferran K., et al. Pontine tegmental cap dysplasia with a 2q13 Microdeletion involving th NPHP1gene: Insights into malformations of the mid-hindbrain. Semin Pediatr Neurol 2010: 17; 69-74.

5. Kono, T., et al. Narrow Duplicated Internal Auditory Canal. Archives of Otolaryngology Head and Neck Surgery 2009; 135: 1048-1051.

CONCLUSIONS

DISCUSSION

METHODS

REFERENCES

Bilat

Bilat

Bilat.

Acccanal

Small

Small

SmallL>R

IAC

AbsentDef R, LNLMildPatient 3

AbsentNLNLMildPatient 2

AbsentDef RNLNLPatient 1

8th7thVestibuleCochlea

ABSTRACT

CONTACT

RESULTS

IAC=internal auditory canal; Acc=accessory canal; NL=normal; Mild=mild cochlear dysplasia; Def=deficient;

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+

+

Neuro-trophicCornea

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-

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Seizure

--+TermPatient 3

+-+TermPatient 2

+-+TermPatient 1

Dev. Delay

VII Paralysis

Profound SNHLBirth

Pontine Tegmental Cap Dysplasia is a novel brain malformation, with only 15 cases described in the literature. Features include vermian hypoplasia, subtotal absence of the middle cerebellar peduncles,flattened ventral pons, vaulted pontine tegmentum, molar tooth appearance of the pontomesencephalic junction, and absent inferior olivary prominence.

Clinical findings are variable, and may include developmental delay, rib and/or vertebral malformations, ocular abnormalities, impaired swallowing, epilepsy, and ataxia. Cranial nerve involvement may include 5, 7, and/or 9; however, 8 appears universally involved.

Figures 1a, 2a and 3a, are midline sagittal T1 weighted images showing the typical appearance of the brainstem in PTCD which includes; flattening of the ventral pons, a thin isthmus (ponto-mesencephalic junction), caplike bulging of the dorsal upper pons (yellow arrow) protruding into the 4th ventricle, and vermian hypoplasia, which was most severe in patient 3. There is also a lipoma present within the interpeduncular cistern (white arrow).

No previous case series have looked specifically at the course of the cranial nerves and the status of the labyrinth. We describe 3 new cases of PTCD and look specifically at the course of the 7th and 8th cranial nerves in these patients, in an effort to anatomically explain sensorineural hearing loss in these patients.

Clinical Characteristics+ feature present; - feature not presentLegend for Figures

Patient 1, Figs. 1b. Sagittal 3D T2 image through the mid IAC and CP angle. The IAC is empty with no 7th

or 8th nerve seen (blue arrow). 1c. Axial CT shows left accessory seventh canal (pink arrow).

Patient 2, Figs. 2b. Sagittal 3D T2 image mid IAC shows an empty IAC (blue arrow) and accessory IAC with seventh cranial nerve (pink arrow). 2c, Axial 3D T2 image lower pons shows a deficient right 7th nerve with both 7th nerves exiting abnormally posterior from the brainstem (pink arrows). 2d, Axial 3D T2 image slightly superior. Accessory 7th canals are seen with the facial nerve demonstrated entering (pink arrows).

Patient 3, Figs. 3b. Sagittal 3D T2 image mid IAC. No nerves are demonstrated. 3c. Axial CT superior to a small IAC shows the left accessory 7th canal (arrow). 3d. Axial 3D T2 image at the same level show the fluid filled accessory canals (pink arrows). Hypoplastic middle cerebellar peduncles are present (blue arrows), which are seen in PTCD.

Fig. 3a, Patient 3

Fig. 2a, Patient 2 Fig. 2b, Empty IAC, Accessory 7th

Fig. 3b, Empty IAC Fig. 3c, CT, Accessory 7th canal Fig. 3d, MR, Accessory 7th canal

Fig. 2c, Aberrant 7th Fig. 2d, Accessory 7th nerve canals

Imaging Findings

Fig. 1b, Empty IACFig. 1a, Patient 1 Fig 1c, CT, Accessory 7th canal