Epidermoid

Introduction

Epidermoid tumors are also called pearly tumors and cholesteatomas, and are benign tumors that account for approximately 0.1% of all intracranial tumors. ^, They typically arise from displaced dorsal ectodermal cell rests during neural tube closure between the third and fifth weeks of embryogenesis. ^, These lesions grow by accumulation of keratin and cholesterol from breakdown or desquamation of epithelial cells and tend to grow along the cisternal spaces. ^, This growth allows them to reach large sizes before they exert clinically significant mass effect, and typically present with cranial nerve symptoms. The goal of surgical treatment is complete resection with preservation of neurologic function, but truly complete resection is challenging, as these lesions are typically adherent to cranial nerves, reach large sizes, and reside in difficult to visualize cisternal spaces. The most common locations are the cerebellopontine angle (CPA) and parasellar locations, in which approximately 40% occur in the CPA. ^, In this chapter, we present a case of a patient with a CPA epidermoid.

Example case

Chief complaint: headaches, nausea, imbalance

History of present illness

A 30-year-old, right-handed woman with no significant past medical history presented with progressive headaches, nausea, and imbalance. Over the past 3 months, she complained of progressive headaches with more frequent nausea without vomiting. In addition, she felt as though her coordination was off in which she felt like she was swaying ( Fig. 75.1 ).

Medications : None.
Allergies : No known drug allergies.
Past medical and surgical history : None.
Family history : No history of intracranial malignancies.
Social history : Restaurant worker, no smoking, occasional alcohol.
Physical examination : Awake, alert, oriented to person, place, time; Cranial nerves II to XII intact; No drift, moves all extremities with good strength; Right greater than left finger-to-nose-dysmetria.

	Bernard R. Bendok, MD, Devi Prasad Patra, MD, Mayo Clinic, Phoenix, AZ, United States	Michael T. Lawton, MD, Barrow Neurological Institute, Phoenix, AZ, United States	Reid C. Thompson, MD, Vanderbilt University, Nashville, TN, United States	Gelareh Zadeh, MD, PhD, Farshad Nassiri, MD, Toronto Western Hospital, Toronto, Canada
Preoperative
Additional tests requested	Audiogram ENT evaluation Swallow and vocal cord evaluation Anesthesia evaluation	High-resolution MRI	Audiogram Neuro-otology evaluation	Audiogram Neuroophthalmology evaluation CTA/CTV
Surgical approach selected	Right far lateral retrosigmoid craniotomy	Stage 1–Right retrosigmoid craniotomy Stage 2–right pterional craniotomy	Right retrosigmoid craniotomy	Right retrosigmoid craniotomy
Anatomic corridor	Right far lateral retrosigmoid	Right retrosigmoid and right trans-Sylvian	Right retrosigmoid, CPA	Right retrosigmoid, CPA
Goal of surgery	Complete resection with preservation of cranial nerve function	Gross total resection	Maximal resection with preservation of cranial nerve function	Maximal safe resection, decompression of brainstem and neural structures, preservation of lower cranial nerves
Perioperative
Positioning	Right lateral park bench	Stage 1–Right lateral Stage 2–Right supine	Right park bench	Right park bench
Surgical equipment	Surgical navigation IOM (EMG for facial and lower nerves, BAERs) Surgical microscope Ultrasonic aspirator Doppler	Surgical navigation IOM (EMG for cranial nerves) Surgical microscope	Surgical microscope IOM (cranial nerve VII EMG, BAERs)	Surgical navigation Surgical microscope IOM Doppler
Medications	Steroids Mannitol, hypertonic saline	Steroids	Steroids Mannitol	Steroids Mannitol
Anatomic considerations	Cranial nerves III–XII, PICA, AICA, SCA, PCA, basilar, vertebral, brainstem	Cranial nerves	Cranial nerves arterial branches off of basilar, brainstem, cerebellum	Transverse-sigmoid sinuses, cranial nerves III–XII, mastoid air cells, vertebral artery/AICA/SCA
Complications feared with approach chosen	Hearing loss, facial weakness, lower cranial nerve dysfunction, vasospasm, chemical meningitis, vascular injury to PICA/AICA/veterbral, venous sinus injury, brainstem injury, cerebellar swelling	Cranial neuropathy	Hearing loss, lack of visualization	Cranial nerve injury, venous sinus injury
Intraoperative
Anesthesia	General	General	General	General
Skin incision	Hockey stick from 1 cm behind mastoid centered at asterion extending to above inion and then below to C2 spinous process	Stage 1–linear Stage 2–pterional	Sigmoid	Sigmoid
Bone opening	Retrosigmoid, suboccipital, right medial one-third occipital condyle, medial posterior arch of C1	Stage 1–retrosigmoid Stage 2–frontotemporal	Retrosigmoid, suboccipital	Retrosigmoid, suboccipital with foramen magnum +/– C1 lamina
Brain exposure	CPA and right cerebellum	Stage 1–CPA and right cerebellum Stage 2–frontotemporal	CPA and right cerebellum	CPA and right cerebellum
Method of resection	Hockey stick incision, form skin flaps along paraspinal and nuchal muscles, suboccpital bone exposed inferiorly to foramen magnum laterally up to transverse/sigmoid junction and digastric groove as well as posterior arch of C1 and C2, burr hole made medial and inferior to the asterion with navigation confirmation, second burr hole lateral to midline, craniotomy made after separating dura, bone drilled to expose edges of transverse and sigmoid sinus, coagulate mastoid emissary vein, removal of suboccipital bone and foramen magnum and posterior arch of C1 approximately 1.5 cm from midline, T-shaped dural opening based on transverse-sigmoid sinus, CSF drainage from cisterns and reverse Trendelenburg positioning, separate arachnoid layer over epidermoid with microscopic visualization starting in middle and proceeding superiorly and inferiorly, identify and separate cranial nerves VII/VIII and AICA, separate lower cranial nerves/PICA/vertebral artery from tumor, separate trigeminal nerve and SCA, as well as cranial nerve VI more medially and cranial nerve IV along tentorium, fine dissection from the brainstem with preservation of perforators and veins, careful inspection of cisterns with mirrors and endoscopes, possible intraoperative MRI or CT, primary dural closure with pericranium and fat if necessary	Stage 1–right retrosigmoid craniotomy up to sinuses, dural opening, relaxation of CSF, dissection in CPA, identify cranial nerves IX–XII/VII–VIII/V, work between nerves with resection up to tentorium Stage 2–reposition, right pterional craniotomy, open dura, trans-Sylvian opening, debulk tumor until no residual	Subperiosteal exposure to foramen magnum including transverse-sigmoid junction, suboccipital craniotomy approximately 4 cm, wax mastoid air cells, open dura, enter cisterna magna and relax CSF, minimize retraction on cerebellum but can place fixed brain retractors if necessary, remove epidermoid piecemeal under microscopic visualization, have neuro-otology on standby for tumor in IAC, early identification of cranial nerves VII and VIII, gentle microdissection away from lower cranial nerves, debulk tumor enough to see vasculature including basilar perforators, deliver rostral component if comes easily with awareness of PCA, decompress cranial nerve 5, remove tumor that delivers easily, leave small sheets of tumor along critical neurovasculature structures if difficult to dissect, dural closure with dural substitute	Subcutaneous tissue and muscles divided to expose posterior fossa to level of C2 lamina, harvest pericranial graft for closure, map transverse-sigmoid sinus with navigation, burr hole placed inferomedial to transverse-sigmoid junction and 3-cm craniotomy to level of foramen magnum and exposure of edges of transverse and sigmoid sinuses, removal of foramen magnum +/– C1 laminectomy, wax mastoid air cells, bring microscope in, Y-shaped dural opening, open cisterna magna and drain CSF, no need for retraction of cerebellum, stimulate for facial nerve starting at 1.0 mA and decreasing to 0.1 mA when closer to facial nerve, Doppler to find vertebral artery at craniocervical junction, identify safe entry zone, tumor removal with sequential intracapsular debulking and internal decompression with ultrasonic aspirator and sharp dissection of capsule from arachnoid, frequent stimulation to monitor cranial nerves, leave capsule if adherent to arachnoid, keep arachnoid plane intact, identify interface of tumor and brainstem with care to protect brainstem venous drainage system, removal of IAC component with drilling bone over canal with diamond drill, follow tumor into middle fossa based on path of tumor, identify fourth nerve near incisura, repair IAC with Tisseel, watertight dural closure with pericranium
Complication avoidance	Large bony opening, meticulous dissection of capsule from the neurovascular structures, leave portion of capsule if adherent to neurovascular structures, minimize manipulation of vessels to avoid spasm, inspection with mirrors and endoscopes, intraoperative imaging, use of fat to augment dural closure	Two-stage approach, large bony opening, identification of cranial nerves	Large bony opening, debulk tumor to find critical neurovasculature structures, remove tumor that delivers itself	Large bony opening, frequent stimulation to monitor cranial nerves, leave adherent capsule behind, keep arachnoid plane intact, follow tumor into middle fossa
Postoperative
Admission	Intermediate unit	ICU	ICU	ICU
Postoperative complications feared	Cranial neuropathy, vasospasm, chemical meningitis, hydrocephalus, CSF leak, brainstem injury, significant residual lesion	Cranial neuropathy, meningitis	Cranial neuropathy (facial weakness, hearing loss, dysphagia), CSF leak, chemical meningitis, delayed hydrocephalus	Cranial neuropathies (facial, lower cranial nerves), venous sinus injury, CSF leak, hydrocephalus, injury to brainstem
Follow-up testing	MRI with DWI within 72 hours, 6 months, 1 year after surgery	MRI within 24 hours after surgery	MRI with DWI night of surgery	MRI with DWI within 48 hours after surgery Audiogram 12 weeks after surgery
Follow-up visits	14 days after surgery 6 weeks, 6 months, 1 year after surgery	14 days after surgery 6 weeks after surgery	14 days after surgery 6 weeks after surgery	4–6 weeks after surgery 6 months after surgery