Skull Base Surgery

Question 1

What are 10 surgical approaches to the sphenoid sinus?

Answer 1

1. Transantral
2. Transpalatal
   - Tumors involving the nasopharynx, posterior pharyngeal wall, and choanae
   - Risk of postoperative VPI
3. Transeptal
   - Sublabial approach
   - Intranasal approach
   - External Rhinoplasty
4. Endoscopic
   - Transnasal
   - Transethmoidal
   - Transantral

Question 2

List the differential diagnosis of primary spheoid masses - 10

Answer 2

A. INFLAMMATORY
1. Mucous retention cyst
2. Mucocele

B. BENIGN
1. Papilloma
2. Fibrous dysplasia
3. Adenoma
4. Fungal ball
5. Clival chordoma

C. MALIGNANT
1. Adenocarcinoma
2. Chondrosarcoma
3. Lymphoepithelioma

Question 3

What are the boundaries of the pituitary fossa/sella turcica?

Answer 3

1. Superior: Tuberculum sellae –> optic chiasm; & Diaphragm sellae
2. Inferior: Sella Turcica –> Sphenoid sinus
3. Anterior: Tuberculum sellae (a bony elevation just posterior to chiasmatic groove and anterior to sella)
4. Posterior: Dorsum sellae
5. Lateral: Cavernous sinus

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Question 4

Discuss the components of the pituitary gland.
What does each component secrete?

Answer 4

1. Adenohypophysis (anterior)
   - Derived from Rathke’s pouch (ectoderm)
   - Secretes ACTH, FSH/LH, GH, PRL, TSH
2. Neurohypophysis (posterior)
   - Axons of cell bodies from supraoptic & paraventricular nuclei of hypothalamus
   - Secretes oxytocin & ADH

Question 5

What is the classification of pituitary adenoma and name the system

Answer 5

Hardy Classification:
1. Grade 1: Microadenoma (< 10mm)
2. Grade 2: Macroadenoma (>10mm)
3. Grade 3: Macroadenoma (>10mm) with focal sellar erosion (outside of sella)
4. Grade 4: Total destruction of sellar floor; Infiltrates sphenoid or cavernous sinus, optic chiasm or cranial nerve compression, and/or invasion into adjacent brain

Question 6

What is the most common type of pituitary adenoma?

Answer 6

Most common = non-secreting
The most common secretory adenoma is a prolactinoma

Question 7

What is the cause of low sodium post-pituitary adenoma surgery?
What are 4 investigational findings on labs/other tests?
What is the treatment? List 4

Answer 7

SIADH = Inappropriate AntiDiuretic Hormone secretion (absorbs water)
- Increased ADH secretion - cannot eliminate free water

Findings:
1. Low serum sodium
2. High urine FeNA (fractional excretion of sodium)
3. High urine specific gravity
4. High urine sodium (>25mequ/L)

TREATMENT:
1. Fluid restriction (< 1L/day)
2. Can consider treating with 3% saline
3. Can consider loop diuretics (e.g. Lasix)
4. Can consider vaptans (tolvaptan); Vasopression (ADH receptor antagonists)
5. Do not increase sodium by more than 12 meq/day - risk of central pontine demyelinosis

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Question 8

Discuss Diabetes Insipidus - what is it? 2
What are the findings? 2
How do you treat it? 2

Answer 8

DIABETES INSIPIDUS:
- Decrease ADH secretion = High urine output (or lack of response to ADH)
- >250mL/hr x 2 hours

Findings:
- Serum Na > 150
- Dilute urine (specific gravity < 1.005)

Treatment:
1. Mild - fluid and electrolyte management
2. Severe - DDAVP - acts as vasopressin (ADH)

Question 9

What are the complications of transphenoidal surgery?
List 9

Answer 9

A. NASAL
1. Saddle nose deformity
2. Perforation
3. Infection
4. Epistaxis

B. CNS
1. CN3-6 injury in cavernous sinus
2. Optic nerve injury
3. CSF leak

C. VASCULAR
1. Cavernous sinus injury
2. ICA injury

Question 10

What are the most common flaps used in skull base reconstruction and what are their blood supplies? 6

Answer 10

1. Nasoseptal flap: Posterior septal artery from the posterior nasoseptal artery (SPA)
   - Can use the entirety of the unilateral septal and floor of nose mucosa with a 1.2mm pedicle
2. Turbinate flap - posterior lateral nasal artery
3. Pericranial flap (letter boxed superiorly)
4. Buccal free mucosal graft
5. Lateral nasal wall mucosal graft
6. Free flap

Question 11

What are the structures of the superior orbital fissure and tendon of Zinn?

Answer 11

ANNULUS OF ZINN:
1. Optic canal
- Optic nerve
- Ophthalmic artery

2. Superior orbital fissure
   - Oculomotor (superior and inferior branches)
   - Abducens (VI)
   - Nasociliary (V1)

SUPERIOR ORBITAL FISSURE:
1. Lacrimal nerve (V1)
2. Frontal nerve (V1)
3. Trochlear nerve (IV)

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Question 12

Describe the features of superior orbital fissure syndrome. 8

Answer 12

INVOLVEMENT:
1. CNIII, IV, V1, VI
2. Differs from orbital apex syndrome in that CN II usually not involved since its in its own canal

CAUSES:
1. Sphenoid sinusitis
2. Neoplasm
3. Trauma

FEATURES:
1. Orbital pain
2. Photophobia
3. Proptosis
4. Ophthalmoplegia
5. Failure of accomodation
6. Upper eyelid paralysis
7. Absence of corneal reflex
8. Forehead paresthesia/hypoesthesia

Question 13

Describe the features of orbital apex syndrome. 5

Answer 13

INVOLVEMENT:
1. CNII, III, IV, VI, V1, V2

Features:
1. Ophthalmoplegia
2. Ptosis
3. Fixed Pupillary dilatation
4. Blindness and decreased visual acuity
5. Anesthesia of upper eyelid and forehead

Basically everything in the back of the orbit

Question 14

Discuss Cavernous Sinus Syndrome:
1. What are the causes?
2. Features? 5
3. Imaging?
4. Treatment?

Answer 14

CAUSES:
1. Ethmoiditis - 80% mortality rate

SYMPTOMS/FEATURES:
1. Orbital pain (V1)
2. Proptosis
3. Photophobia
4. Ophthalmoplegia (CNIII, IV, VI involvement)
5. Venous congestion of retina, lids, conjunctiva

IMAGING:
1. Brain MRI and MR Venography
2. CT Venogram if MR not available

TREATMENT:
1. Antibiotics
2. Anticoagulation

Question 15

Differentiate Orbital apex, superior orbital fissure, and cavernous sinus syndrome based on the nerves involved and not involved

Answer 15

ORBITAL APEX SYNDROME:
- Involved: 2, 3, 4, 6, ± V1/V2 (from inferior orbital fissure)

SUPERIOR ORBITAL FISSURE SYNDROME:
- Involved: 3, 4, 6, ± V1
- Not involved: 2

CAVERNOUS SINUS SYNDROME:
- Involved: 3, 4, 6, ± V2
- Not involved: 2, V1 (except ophthalmic branch)

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Question 16

Discuss Oculomotor (CNIII) nerve palsy:
1. What muscles does it innervate? 5
2. What are the clinical features? 4

Answer 16

MUSCLES:
1. Superior rectus
2. Inferior rectus
3. Medial rectus
4. Inferior oblique muscle (extorsion, elevation, abduction)
5. Levator palpebrae

Features of palsy:
1. Diplopia and ptosis
2. Pupil normal or dilated (mydriasis)
3. Response to direct light may be sluggish or absent (efferent defect)
4. Gaze: Deviate out and down (with straight gaze) - superior oblique making you look down, lateral rectus making you look out

Movements:
- Adduction is slow and may not proceed past the midline
- Upward gaze is impaired
- Downward gaze: superior oblique muscle causes the eye to adduct slightly and rotate inward

Vancouver 454 - EYE MOVEMENTS DIAGRAM!!

Question 17

Discuss Trochlear (CNIV) nerve palsy:
1. What muscles does it innervate?
2. What are the clinical features?

Answer 17

MUSCLE: Superior oblique muscle (intorsion, depression, abduction)

FEATURES:
1. Vertical diplopia
2. Difficult looking down and inward - makes going downstairs difficult
- Can tilt the head to the side opposite which can compensate and eliminate the diplopia

Question 18

Discuss Abducens (CNVI) nerve palsy:
1. What muscles does it innervate?
2. What are the clinical features?

Answer 18

MUSCLES: Lateral rectus ipsilateral, partially contralateral medial rectus
- Palsy of this causes ipsiliateral medial rectus muscle to be unopposed

FEATURES:
1. Binocular horizontal diplopia when looking to lesioned side
2. Eye is slightly adducted at rest
3. Abduction is sluggish, and when maximal abduction, lateral sclera is exposed

Question 19

If you have a CSF leak of the anterior skull base, what is the size of defect that is suitable for:
1. Mucosa only coverage
2. Composite (multilayer coverage)

Answer 19

• Mucosa only coverage: < 3 or 5mm - mucosal defect
• Composite coverage: > 3 or 5mm mucosal defect or >2cm bone defect

Question 20

Define a complete classification and differential for CSF rhinorrhea

Answer 20

TRAUMATIC VS. NON-TRAUMATIC

TRAUMATIC:

A. ACCIDENTAL
1. Immediate
2. Delayed

B. SURGICAL
1. Complication of neurosurgical procedures
- Transsphenoidal hypophysectomy
- Frontal craniotomy
- Other Skull base procedures
2. Complication of rhinologic procedures
- Sinus surgery
- Septoplasty
- Other combined SB procedures

NON-TRAUMATIC

A. ELEVATED INTRACRANIAL PRESSURE
1. Intracranial neoplasm
2. Hydrocephalus (Non-communicating vs. Obstructive)
3. Benign intracranial hypertension
4. Normal intracranial hypertension

B. CONGENITAL ANOMALY

C. SB NEOPLASM
1. Nasopharyngeal carcinoma
2. Sinonasal tumors

D. SKULL BASE EROSIVE PROCESS
1. Sinus mucocele
2. Osteomyelitis
3. Granulomatous inflammatory processes (e.g. GPA)

E. IDIOPATHIC

Question 21

What is the prevalence of the main etiologies for CSF leak?

Answer 21

1. 80% accidental trauma
2. 16% iatrogenic
3. 4% varied etiologies

Statpearls

Question 22

What is the differential diagnosis of CSF rhinorrhea that may not be CSF? 4

Answer 22

1. Retained nasal irrigation fluid
2. Ruptured sinus retention cyst
3. Sinonasal inflammatory conditions
4. Allergic or vasomotor rhinitis

Question 23

What are two areas of inherent skull base weakness (anteriorly)?

Answer 23

1. Long lamella of cribriform plate (weaker if longer)
2. Persistence of lateral craniopharyngeal (Sternberg’s) canal

Question 24

What are two factors that must exist for a CSF leak to occur?

Answer 24

1. Disruption of barriers (arachnoid and dura mater, paranasal sinus mucosa, and bone)
2. Pressure gradient to produce flow of CSF

Question 25

For an anterior skull base CSF leak, what are the ways to diagnose a CSF Leak? 7

Answer 25

1. BETA-2 TRANSFERRIN - Most common protein in CSF - Transportation time may degrade sample - Also present in: aqueous humor, perilymph, serum of patients with alcohol-related chronic liver disease, patients with inborn errors of metabolism 2. BETA-2 TRACE - Second most common protein in CSF - Produced by meninges and choroid plexus - Present in serum (much lower concentration) - 100% sensitivity and specificity - Unreliable in patients with renal insufficiency or bacterial meningitis 3. POSITION OF SKULL BASE DEFECT - Require an active leak to identify location (can be challenging when leak is intermittent) 4. INTRATHECAL FLUORESCEIN - Requires LP - Dilution of 0.1ml of 10% fluorescein in 10cc patients own CSF, infused over 30 minutes 5. RADIONUCLEOTIDE (Radioactive iodine serum albumin, technetium-labelled serum albumin, indium-labelled) - Requires LP - Cannot be sole test for CSF leak due to unacceptable rate of false-positives and indeterminate results - Intranasal pledgets placed in close proximity to skull base and assayed for tracer 12-24 hours latera - Limited by poor spatial resolution 6. CT CISTERNOGRAPHY - Requires LP - 80% CSF leak can be confirmed through CT cisternography 7. MRI CISTERNOGRAPHY - No LP requires - Heavily T2-weighted image with fat suppression and video reversal - Thick image slices may not identify small skull base defects - Detail of soft tissue (coincident meningocele, empty sella)

Question 26

List 9 complications of intrathecal fluorescein

Answer 26

1. Generalized seizures 2. Opisthotonos (hyperextension and spasticity) 3. Lower limb weakness/paresthesia 4. Headache 5. Cranial nerve deficits Dizziness NV Pulmonary edema Death

Question 27

Describe the 3 conservative treatment for CSF leak

Answer 27

1. 1-2 weeks strict bed rest with head elevation 2. Continuous subarachnoid drainage with LP 3. Avoid coughing, sneezing, nose blowing, straining (stool softener recommended) Similar to post-op care: 24h bed rest, HOB elevated, avoid valsalva/intracranial pressure, stool softeners, lumbar drain at 10cc/h for 24-48 hours

Question 28

Indication for operative CSF leak repair

Answer 28

1. Failed conservative management 2. Intraoperative leak - large defects/leaks 3. Idiopathic leaks 4. Open traumatic head wounds with CSF leak

Question 29

What are 3 approaches to anterior skull base CSF leak repair?

Answer 29

1. Intracranial 2. Extracranial (external) 3. Endoscopic Can be overlay or underlay (>5mm) Usually a sandwich technique (inlay followed by overlay)

Question 30

Describe briefly how to perform a transcranial repair of anterior SB CSF leak. What are 3 different graft materials that can be used? What are 4 complications?

Answer 30

1. Craniotomy, identify defect, tissue graft placed Graft: 1. Fascia lata 2. Fat plug 3. muscle plug 4. pedicled galeal flap High failure rate: 25% Complications: 1. Brain compression 2. Hematoma 3. Seizure 4. Anosmia

Question 31

Describe briefly how to perform a extracranial repair of an anterior SB CSF leak. When can you use a mucosal graft vs. composite closure? What are 8 options for graft material?

Answer 31

1. Endoscopic dissection to visualize skull base 2. Intrathecal fluorescein may be administered 3. Bipolar any concomitant meningoencephalocele 4. Mucosa within 5mm margin of defect is removed 5. Repair defect with graft based on a no-flow, low-flow, or high-flow approach A. No Flow = free mucosal graft B. Low-flow = Multilayer closure with autografts and/or synthetic dural replacement C. High-flow = Multilayer reconstruction with autografts, synthetic dural replacements, and vascularized tissue flaps Graft Material (choice does not seem to alter outcome of repair) 1. Temporalis fascia 2. Fascia lata 3. Fat plug 3. Muscle plug 4. Pedicled middle turbinate flap 5. Free cartilage graft 6. Free bone graft 7. Acellular dermal allograft 8. Autogenous fat

Question 32

Regarding Pseudotumor Cerebri Syndrome, discuss: 1. What are the other names for this? 2 2. Pathophysiology? 3. Epidemiology, what do the patients typically stereotype like?? 3 4. Symptoms? 4 5. Diagnosis? Outline the whole criteria 4 7. Management? 7

Answer 32

PSEUDOTUMOR CEREBRI SYNDROME - Aka. Idiopathic intracranial hypertension (IIH) - Aka. Benign intracranial hypertension (BIH) PATHOPHYSIOLOGY: Unclear EPIDEMIOLOGY: 1. Women of child-bearing age 2. Obese 3. F:M 3:1 SYMPTOMS: 1. Headache 2. Visual changes: (a) transient visual obscuration lasting seconds at a time (unilateral or bilateral); (b) loss of visual acuity; (c) visual field loss; (d) Diplopia - rare 3. Unilateral pulsatile tinnitus 4. Can present with a CSF leak (ear or nose) DIAGNOSIS: MODIFIED DANDY CRITIERA (most widely accepted) ALL of the following much be met: 1. Symptoms and signs of increased intracranial pressure (headache, transient visual obscuration, pulse synchronous tinnitus, papilledema, visual loss) 2. No other neurological abnormalities or impaired level of consciousness 3. Elevated intracranial pressure (≥200mmH2O) with normal CSF composition (on LP) 4. A Neuroimaging study that shows no etiology for intracranial hypertension (need to order an MRI standard) MANAGEMENT: A. Medical 1. Weight loss 2. Low sodium diet 3. Acetazolamide (diuretic that decreases IOP) 4. Topiramate (carbonic anhydrase activity and headaches management) 5. Lasix (not very effective) B. Surgical 1. Optic nerve sheath fenestration (for visual loss) 2. VP shunting ## Footnote Vancouver 456 Normal optic nerve: https://prod-images-static.radiopaedia.org/images/148/5c6cd30d7250650becbd1c6659220f_big_gallery.jpeg

Question 33

What are the imaging findings of BIH? 7

Answer 33

IMAGING: 1. Normal CT usually 2. Empty sella 3. Slit like ventricles 3. Posterior aspect of the globe flattening 4. Perioptic arachnoid space distension (prominence subarachnoid space around the optic nerves) 5. Turtuous optic nerves 6. Transverse venous sinus stenosis - collapsible portions of the sinuses; superior sinus is incorporated in dura and sigmoid sinus is outside the cerebrum, high pressure collapses it SPEFTT Slit like ventricles Perioptic arachnoid space distension (prominent space around optic nerves) Empty sella Flattening of the posterior aspect of the globe Tortuous optic nerves Transverse venous sinus stenosis (collapsable portion of the sinuses)