Brainstem and Cranial Nerves: Pons

The pons extends from the pontomedullary junction to an imaginary line drawn from the exit of cranial nerve IV. Dorsal to the pons lies the cerebellum, which receives information and projects information back to the brainstem through the inferior, middle, and superior cerebellar peduncles. Important structures at this level include the corticospinal tracts, corticopontocerebellar fibers traveling through the middle cerebellar peduncle, the cerebellum, and cranial nerves V through VIII. Blood supply to the pons is from the basilar artery and its perforating vessels.

Fenestration of intracranial neurenteric cyst: A case report

Background: Neurenteric cysts are rare congenital lesions of endodermal origin which result from the failure of the neurenteric canal to close during embryogenesis. The majority of neurenteric cysts occur in the spinal cord, though in rare instances can occur intracranially, typically in the posterior fossa anterior to the pontomedullary junction (80%) or in the supratentorial region adjacent to the frontal lobes (20%). Case Description: We present the case of a 75-year-old woman with an extra-axial cystic lesion centered in the premedullary cistern causing brainstem compression. The lesion was later histopathologically confirmed to be a neurenteric cyst. She presented initially with a 4-month history of worsening headache, dizziness, and unsteady gait. We performed a left retrosigmoid craniotomy for cyst fenestration/biopsy with the aid of operating microscope and stealth neuronavigation. Following the procedure, the patient recovered without complications or residual deficits. Conclusion: This case illustrates the successful fenestration of an intracranial neurenteric cyst with good clinical outcome. We present the pre- and post-operative imaging findings, a technical video of the procedure, histopathological confirmation, and a brief review of the relevant clinical literature on the topic.

Endoscope-assisted microsurgical resection of intrinsic brainstem epidermoid: technical note and review of the literature

Intrinsic epidermoid tumors of the brainstem are rare, histologically benign lesions associated with high surgical morbidity and mortality due to their eloquent location. The authors report a child with progressive severe neurological deterioration from a large midline intrinsic brainstem epidermoid at the pontomedullary junction. The mass was removed through a posterior fossa craniotomy and midline endoscope-assisted microsurgical corridor through the floor of the fourth ventricle, using neurophysiological monitoring. Postoperatively, there was dramatic improvement in the patient’s symptoms. Early recurrence of the mass necessitated reoperation with more aggressive resection of the cyst capsule, which led to complete radiographic reconstitution of the brainstem. The patient remains well with a durable recovery 7 years after presentation. The authors review the literature on brainstem epidermoids and discuss the differential diagnosis and management strategies for approaching these lesions, advocating for conservative surgery with resection of as much of the tumor capsule as is safely possible.

Medial Pontomedullary Stroke Mimicking Severe Bell’s Palsy: A Case Report

Introduction: Patients with acute unilateral upper and lower facial palsy frequently present to the emergency department fearing they have had a stroke, but many cases are benign Bell’s palsy. Case Report: We present a rare case of a medial pontomedullary junction stroke causing upper and lower hemifacial paralysis associated with severe dysphagia and contralateral face and arm numbness. Conclusion: Although rare, pontine infarct must be considered in patients who present with both upper and lower facial weakness. Unusual neurologic symptoms (namely diplopia, vertigo, or dysphagia) and signs (namely gaze palsy, nystagmus, or contralateral motor or sensory deficits) should prompt evaluation for stroke.

External syringomyelia in longstanding benign foramen magnum tumors

Background: The effect of benign foramen magnum tumours on cranial and spinal dimensions and cerebrospinal fluid (CSF) spaces is unclear. In this study, we measured alterations in cerebrospinal fluid (CSF) spaces in the spinal canal and in the posterior cranial fossa distant from the site of benign foramen magnum tumors. Methods: Twenty-nine magnetic resonance imaging scans of patients with foramen magnum tumors (8 meningiomas and 21 C2 neurinomas) were identified for radiological morphometric analysis and compared with normal control scans. The anterior-posterior distance between the pontomedullary junction and the clivus, the spinal canal diameter, spinal cord diameter, and cord-canal ratios were measured at the C6 and T2 levels. Results: The mean spinal canal diameter was significantly higher in tumor scans at both the C6 and T2 spinal levels than in controls (13.8 mm vs. 11.4 mm at C6; p<0.0001, and 12.9 mm vs. 11.9 mm at T2; P=0.01). Further, the mean cord:canal ratio was significantly lower in tumor scans at both levels (0.49 vs. 0.64 at C6; P<0.0001, and 0.45 vs. 0.54 at T2; P=0.0009). There was no significant difference in mean anteroposterior distance from the clivus to the pontomedullary junction (10.4 mm vs. 10.3 mm; P=0.91). Conclusion: In the presence of benign foramen magnum tumors, the spinal canal diameter and CSF volume in the spinal canal increased at the C6 and T2 levels, distant from the tumor site, a phenomenon we describe as “external syringomyelia”.

Resection of brainstem cavernous malformation via perifacial zone through retrosigmoid supracondylar approach

Hemorrhagic brainstem cavernous malformations carry a high risk of progressive neurological deficits owing to recurrent hemorrhages and hence require complete surgical resection while minimizing damage to the dense concentration of nuclei and fibers inside the brainstem. To access lesions inside the lower pons, the senior author (H.B.) has preferred to approach the lesions via the “perifacial zone” through the pontomedullary sulcus from the inferior surface of the pontine bulge for more than 20 years.1,2 This video demonstrates a case of a cavernous malformation inside the lower pons, which was surgically treated via the pontomedullary junction through the retrosigmoid supracondylar approach in a half-sitting position. The lesion was completely removed in piecemeal fashion through a tiny incision on the sulcus, which did not cause any new neurological deficits. The modified Rankin Scale improved from 4 before the surgery to 1, and the patient had no recurrence during the 2 years of follow-up. The advantage of this access and the dissection techniques for this challenging lesion are introduced, based on our experience with more than 230 surgeries of brainstem cavernoma.The video can be found here: https://youtu.be/0H_XqkQgQ9I.

Microsurgical resection of an enlarging lateral pontomedullary cavernous malformation

The extended retrosigmoid approach provides an excellent corridor to the lateral aspect of the pontomedullary junction (PMJ).1,2 This video demonstrates a microsurgical resection of a progressive enlarging cavernous malformation (CM) of the PMJ. The patient is a 33-year-old woman with progressive symptoms, including right facial droop, left hemianesthesia, diplopia, and nystagmus. The patient underwent a right extended retrosigmoid approach with intraoperative neuronavigation and neuromonitoring. Lower cranial nerve dissection allowed access to the lateral PMJ. A longitudinal corticotomy was performed above the glossopharyngeal. The CM was removed in a piecemeal fashion. Postoperative MRI confirmed gross-total resection and the patient remained neurologically stable.The video can be found here: https://youtu.be/K_TtiTo1RsQ.

Hemidysgeusia, phantosmia and respiratory arrest: a case of CLIPPERS

A 56-year-old man presented with a relapse of likely chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids (CLIPPERS) after a reduction of steroid dose. MRI demonstrated new perivascular FLuid-Attenuated Inversion Recovery (FLAIR) signal hyperintensity involving the dorsal pontomedullary junction and progressing inferiorly into the dorsal medulla oblongata. His admission to hospital was complicated by a respiratory arrest.

A midline prepontine cyst: Serial magnetic resonance imaging over 20 years shows very slow growth after its rapid shrinkage

An otherwise healthy 22-month-old boy suffered high fever, irritability, nausea, dysphagia, dysarthria and right hemiparesis. Magnetic resonance imaging showed a cystic mass, 15 mm in diameter, with surrounding oedema in the base of the lower pons. The symptoms subsided in about 10 days after onset, followed by a rapid decrease of the cyst size to 5 mm. Thereafter, the patient’s psychomotor growth has been normal. Annual follow-up magnetic resonance imaging scans showed very gradual enlargement of the cyst located on the ventral surface of the pontomedullary junction, reaching 16 mm in diameter in 21 years after onset. It was hyperintense on T1-weighted and isointense on T2-weighted magnetic resonance imaging. No haemosiderin deposition or gadolinium enhancement was seen. This is a rare report of a two decade longitudinal follow-up of a midline prepontine cyst showing asymptomatic and very slow growth. The possible nature of the cyst includes neurenteric, dermoid and epidermoid cyst.

Extended Retrosigmoid Approach for the Resection of a Pontomedullary Junction Cavernous Malformation

Objectives To describe an extended retrosigmoid approach for the resection of a cavernoma involving the ponto-medullary junction, with emphasis on the microsurgical anatomy and technique. Design A retrosigmoid craniotomy is performed in the lateral decubitus position and the sigmoid sinus exposed. After opening the dura, sutures are placed medial to the sinus to allow its gentle mobilization. Cerebrospinal fluid (CSF) is drained from the cisterna magna, and cerebellopontine cistern, and dynamic retraction is used over the cerebellum. Subarachnoid dissection of the cerebellopontine angle gives access to cranial nerves IX/X, VII/VIII, and VI. Inspection of the pontomedullary junction medial to the facial nerve reveals hemosiderin staining in that region. A small pial opening is made, exposing the hemorrhagic cavity. The cavernous malformation is then identified, dissected circumferentially, and resected. Photographs of the region are borrowed from Dr Rhoton's laboratory to illustrate the microsurgical anatomy. Participants The senior author performed the surgery. The video was edited by Drs. J.B. and V.N. Outcome Measures Outcome was assessed with extent of resection and postoperative neurological function. Results A gross total resection of the lesion was achieved. The patient did not develop any postoperative deficits. Conclusion Understanding the microsurgical anatomy of the cerebellopontine angle and meticulous microneurosurgical technique are necessary to achieve a complete resection of a brainstem cavernoma. The extended retrosigmoid approach provides an adequate corridor to the pontomedullary junction.The link to the video can be found at: https://youtu.be/FIKixWJT75w.