Trigeminal schwannomas

Introduction

Trigeminal schwannomas are rare benign primary intracranial tumors that arise from Schwann cells that are responsible for the myelin sheath around the nerve axons. They make up 0.1% to 0.4% of all intracranial tumors and 1% to 8% of intracranial schwannomas. These tumors can develop anywhere along the trigeminal nerve from the brainstem origin or the cisternal location to the peripheral divisions of the ophthalmic, maxillary, and mandibular divisions. Depending on their origin, these tumors can be intradural, extradural, intracranial, or extracranial. As a result, there are a variety of surgical approaches that have been developed for these tumors depending on tumor location, patient characteristics, and surgeon preference. In this chapter, we present a case of a patient with a trigeminal schwannoma.

Example case

Chief complaint: headaches and left facial numbness

History of present illness

A 65-year-old, right-handed man with a history of hypertension, hypercholesterolemia, and depression presented with headaches and left facial numbness. For the past 3 to 6 months, he had complained of worsening headaches and numbness in the upper and lower jaw on the left side. He had undergone prior imaging, and there was notable interval growth of a left-sided brain lesion ( Fig. 69.1 ).

Medications : Aspirin, lisinopril, atorvastatin, sertraline.
Allergies : No known drug allergies.
Past medical and surgical history : Hypertension, hypercholesterolemia, depression, appendectomy, right carpal tunnel, left meniscus.
Family history : No history of intracranial malignancies.
Social history : Nurse, no smoking or alcohol.
Physical examination : Awake, alert, oriented to person, place, time; Cranial nerves II to XI, except left V2 to V3 facial numbness; Moves all extremities with good strength.

	Michael R. Chicoine, MD, Washington University, St. Louis, MO, United States	William T. Couldwell, MD, PhD, University of Utah, Salt Lake City, UT, United States	Eslam Mohsen Mahmoud Hussein, MBBS, MSc, Ain Shams University, Cairo, Egypt	Graeme F. Woodworth, MD, University of Maryland, Baltimore, MD, United States
Preoperative
Additional tests requested	CT and CTA Audiogram	CT	CT EEG Audiogram	CT
Surgical approach selected	Left middle fossa craniotomy with lumbar drain +/– abdominal fat graft	Left middle fossa craniotomy	Left temporal craniotomy with posterior petrosectomy	Left temporal and subtemporal craniotomy
Other teams involved during surgery	ENT	None	ENT	None
Anatomic corridor	Left middle fossa	Left middle fossa, extra- and intradural	Left subtemporal with posterior petrosal	Left subtemporal
Goal of surgery	Maximal resection with preservation of neurologic function, diagnosis	Gross total resection	Radical resection	Gross total resection, diagnosis, nerve preservation
Perioperative
Positioning	Left supine with right rotation	Left lateral	Left supine with 70-degree right rotation	Left supine with lateral head position
Surgical equipment	Lumbar drain Surgical navigation IOM (SSEP, MEP, EMG of cranial nerves VII–VIII) Surgical microscope Microdoppler	Surgical navigation IOM (SSEP, MEP) Surgical microscope Ultrasonic aspirator	Surgical navigationIOM (SSEP, MEP, EMG of cranial nerves VII-VIII)Surgical microscope Ultrasonic aspirator	Surgical navigation Surgical microscope IOM (SSEP)Ultrasonic aspirator
Medications	Steroids Mannitol Antiepileptics	Steroids Mannitol	AntiepilepticsSteroids	Steroids Mannitol Antiepileptics
Anatomic considerations	Superficial temporal artery, temporal bone, floor of middle fossa (arcuate eminence, GSPN, ICA, MMA, cranial nerves V/VII/VIII), vein of Labbe, left temporal lobe	Meckel cave, greater superficial petrosal nerve	Vein of Labbe, greater superficial petrosal nerve, Meckel cave	Temporal lobe, vein of Labbe, optic nerve, trochlear nerve, trigeminal nerve, PCOM
Complications feared with approach chosen	Injury to temporal lobe, vein of Labbe, petrous ICA, cranial nerves V/VII/VIII, CSF leak	Subtotal resection	Temporal lobe venous infarct	Temporal lobe injury, venous infarct
Intraoperative
Anesthesia	General	General	General	General
Skin incision	Curvilinear preauricular	Linear	Linear	Inverted U over EAM
Bone opening	Left frontotemporal	Left temporal	Left temporal and posterior petrous	Left temporal, subtemporal
Brain exposure	Left temporal lobe	Left temporal lobe	Left temporal	Left temporal lobe
Method of resection	Placement of lumbar drain, neck and abdomen prepped, myocutaneous flap, frontotemporal craniotomy down to zygoma, extradural dissection of middle fossa, coagulation of MMA and sectioning, identify V3 at foramen rotundum/arcuate eminence/GSPN, petrous ICA, Meckel cave, direction stimulation of GSPN, base of the tumor dissected from cranial nerve V with sharp dissection, additional drilling of petrous bone if needed, dura opened on temporal floor to separate tumor from inferior temporal lobe, tumor debulked, dural closure with dural substitute, obliterate mastoid air cells with fat if needed	Craniotomy centered over root of zygoma, bone wax to tegmen tympani, subtemporal extradural dissection identifying GSPN, enter into Meckel cave, debulk tumor, open temporal dura and debulk more tumor	Left temporal craniotomy, exposure of the Trautman triangle, opening of dura across middle cranial fossa to protect vein of Labbe, division of superior petrosal sinus, resection of tentorium cerebelli, exposure of lateral brainstem, debulking of tumor	Possible lumbar drain, inverted U-shaped incision based on EAM, temporal craniotomy based on navigation that is low to the skull base, cruciate dural opening, relax brain with CSF diversion and gentle brain retraction under microscopic visualization, biopsy and internal debulking of tumor, if frozen reveals radiosensitive tumor then less aggressive approach
Complication avoidance	Lumbar drain, identify skull base anatomy, extradural dissection, sharp dissection from nerves, leave tumor if cannot be separated from nerve, obliterate air cells with fat	Identification of GSPN, bone wax to skull base, intra- and extradural tumor removal	Protect vein of Labbe, expose middle and posterior cranial fossa	Possible lumbar drain, relax brain with CSF drainage early, care taken to avoid venous injury, goal of resection depending on frozen pathology
Postoperative
Admission	ICU	ICU	ICU	ICU
Postoperative complications feared	Temporal lobe swelling, CSF leak, facial numbness or pain, diplopia, facial weakness, hearing loss, dry eye	CSF leak	Temporal lobe infarction, seizures	Temporal lobe edema, venous infarction, seizures
Follow-up testing	MRI 3–6 months after surgery Audiogram	MRI within 24 hours after surgery	CT immediately after surgery MRI 2 months after surgery	CT immediately after surgery MRI within 24 hours after surgery, 4–6 weeks after surgery
Follow-up visits	2–3 weeks after surgery	1 month after surgery	2 months after surgery	2 weeks, 4–6 weeks after surgery

Adjuvant therapies recommended	Observation vs. SRS	Observation, radiation if regrows	SRS	Observation for small residual, SRS for large residual