Pontine brainstem low-grade glioma

Introduction

Surgery in the brainstem can be associated with significant morbidity and mortality. ^, This is because the brainstem has a high density of eloquent gray and white matter structures, including cranial nerve (CN) nuclei, CN tracts, and craniospinal tracts, among others. ^, With a better understanding of brainstem anatomy, improved neuroimaging, and advances in surgical techniques and monitoring, surgery within the brainstem can occur with reduced morbidity. ^, In this chapter, we present a case of dorsal pontine brainstem lesion.

Example case

Chief complaint: left facial weakness

History of present illness

A 19-year-old, right-handed woman with no significant past medical history presented with prolonged facial weakness. Six months prior she developed left-sided facial weakness with inability to close her eye. She was treated for Bell palsy with steroids with no improvement after 6 months. Imaging was done and revealed a brain lesion ( Fig. 13.1 ).

Medications : None.
Allergies : No known drug allergies.
Past medical and surgical history : None.
Family history : No history of intracranial malignancies.
Social history : College student. No smoking or alcohol.
Physical examination : Awake, alert, oriented to person, place, and time; Language: intact naming and repetition; CNs II to XII intact except left House-Brackmann 5/6; No drift, moves all extremities with full strength.

	Clark C. Chen, MD, PhD, University of Minnesota, Minneapolis, MN, United States	Shlomi Constantini, MD, Danil A. Kozyrev, MD, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel	George I. Jallo, MD, Johns Hopkins All Children’s Hospital, St. Petersburg, FL, United States	Vicent Quilis-Quesada, MD, PhD, University of Valencia, Valencia, Spain
Preoperative
Additional tests requested	Spine MRI Neuroophthalmology evaluation ENT evaluation Speech and swallow evaluation Intraoperative MRI	Diffusion MRI Spine MRI	Spine MRI	Spine MRI Lumbar puncture/CSF analysis DTI Echocardiogram
Surgical approach selected	Midline suboccipital craniotomy with intraoperative MRI	Midline suboccipital craniotomy for open biopsy	Midline suboccipital craniotomy	Midline suboccipital craniotomy
Anatomic corridor	Telovelar	Target inferior medullary aspect	Left telovelar	Left telovelar
Goal of surgery	Diagnosis, maximal resection	Diagnosis	Maximal resection without neurological deficit	GTR
Perioperative
Positioning	Prone	Prone	Prone	Semisitting
Surgical equipment	Surgical navigation IOM (MEP, SSEP, BAERs, facial nerve EMG) Intraoperative MRI with 5-ALA	Ultrasound IOM Surgical microscope Electrified ultrasonic aspirator	Surgical navigation IOM (SSEP, MEPs, BAERs, cranial nerve EMG) Ultrasound Surgical microscope Nerve stimulator	IOM (SSEP, MEPs, BAERs, cranial nerve EMG) Surgical microscope Ultrasonic aspirator
Medications	Steroids Mannitol	Steroids	Steroids	None
Anatomic considerations	Inion, foramen magnum, C1, torcula, transverse sinus, sulcus arteriosus	Cerebellar tonsils	Cerebellar tonsils, PICA, floor of fourth ventricle	Floor of the fourth ventricle, PICA, dentate nuclei
Complications feared with approach chosen	Venous sinus and vertebral artery injury, brainstem/spinal cord injury	Injury to cranial nerves VI–VII, paramedian pontine reticular formation	Injury to cranial nerves at fourth ventricular floor, PICA stroke	Venous air embolism
Intraoperative
Anesthesia	General	General	General	General
Skin incision	Midline linear from 1–2 cm above inion to C1	Midline linear from under inion to C2	Midline linear from under inion to C2	Midline from inion to C2
Bone opening	Midline occipital bone below transverse sinus, including foramen magnum	Midline occipital bone below transverse sinus, including foramen magnum	Midline occipital bone below transverse sinus, including foramen magnum	Midline occipital bone 1 cm below superior nuchal line, including foramen magnum
Brain exposure	Cerebellum, tonsils	Cerebellum	Cerebellum, tonsils	Cerebellum, tonsils
Method of resection	Mark Frazier burr hole, incision with preservation of the pericranium, midline muscle dissection with exposure of C1, midline craniotomy, Y-shaped dural opening, open cerebellomedullary fissure, dissect up to rostral half of fourth ventricle, identify abnormal region and confirm with navigation, establish new baseline IOM, biopsy lesion, repeat IOM, debulk lesion and attempt to identify plane, intraoperative MRI to assess need for further resection, watertight closure with pericranium, bone flap fixation	Midline muscle dissection, stripping muscle from C1 and atlanto-axial membrane, midline craniotomy below transverse sinus, opening of foramen magnum, midline Y-shaped dural opening, separate tonsils to visualize the fourth ventricle, biopsy of exophytic medullary component leaving floor of fourth ventricle intact	Midline muscle dissection, exposing C1 lamina, midline occipital craniectomy below sinus incorporating foramen magnum, midline Y-shaped dural openings, section arachnoid between tonsils, identifying and incising tela choroidea +/– inferior medullary velum on left, ultrasound probe and navigation to confirm lesion location if not readily apparent on fourth ventricular floor, stimulate with nerve stimulator to confirm no facial nerve activity, intralesional debulking with suction, stop if lesion is fibrous or neuromonitoring changes, watertight dural closure with synthetic graft, bone flap fixation	Midline muscle dissection, suboccipital craniotomy, Y-shaped dural openings, cerebellomedullary fissure dissection, left tonsil dissection and left PICA protection, open vallecula to expose fourth ventricle, division of inferior medullary velum and tela choroidea, removal of inferior part of the lesion, expose left MCP and SCP and remove remainder, reconstruct cisterna magna with 9-0 suture, watertight dural closure, bone flap fixation
Complication avoidance	Frazier burr hole preparation, pericranium for closure, opening foramen magnum, telovelar approach, repeated IOM, intraoperative MRI	Separate muscle from atlanto-occipital membrane, opening foramen magnum, working between cerebellar tonsils, biopsy only exophytic medullary component, leave floor of fourth ventricle intact	Opening foramen magnum, left-sided telovelar opening, ultrasound and navigation to confirm lesion, nerve stimulator to identify safe entry zone, intralesional debulking	IOM, left PICA identification and protection, telovelar tonsillar opening, removal of inferior or exophytic portion first
Postoperative
Admission	ICU	ICU	ICU	ICU
Postoperative complications feared	Facial nerve injury, cerebellar retraction injury, CSF leak	Loss of cough and gag reflexes, posterior fossa syndrome, eye movement issues	Facial nerve weakness, diplopia, dysphagia, aspiration, CSF leak	Cranial neuropathies, motor deficit, respiratory insufficiency
Follow-up testing	MRI within 48 hours after surgery Swallow evaluation Physical and occupational therapy	MRI within 48 hours after surgery	MRI within 48 hours after surgery Swallow evaluation	MRI within 24 hours after surgery
Follow-up visits	2 weeks after surgery Initiation of radiation/chemotherapy pending diagnosis	14 days after surgery MRI 3 months after surgery	14–21 days after surgery MRI 3 months after surgery	14 days after surgery
Adjuvant therapies recommended
Diffuse astrocytoma (IDH mutant, retain 1p19q)	STR–chemotherapy, delayed radiation for recurrence GTR–observation	STR–radiation/chemotherapy GTR–observation	STR–observation GTR–observation	STR–radiation/PCV GTR–radiation/PCV
Oligodendroglioma (IDH mutant, 1p19q LOH)	STR–radiation/PCV GTR–observation	STR–chemotherapy GTR–observation	STR–observation GTR–observation	STR–radiation/PCV GTR–radiation/PCV
Anaplastic astrocytoma (IDH wild type)	STR–radiation/temozolomide GTR–radiation/temozolomide	STR–radiation +/– chemotherapy GTR–radiation +/– chemotherapy	STR–radiation/temozolomide GTR–radiation/temozolomide	STR–radiation/temozolomide GTR–radiation/temozolomide