Neuro Club: Skull Base Tumours - Case Based Learning Session

1. Suggested Topic List for the Session

2. The CBL Case: "The Woman Who Almost Got a Psychiatric Referral"

Tumour: Vestibular Schwannoma (Right CPA)

PATIENT SCRIPT

Character Name: Mrs. Amara Osei, 44F

Instructions for the actor: You are a patient, NOT a doctor. You don't know your diagnosis. Answer only what is asked. Use the responses below. If asked something not covered, improvise naturally based on your symptoms. Be slightly nervous. You have been told by two previous doctors this is "probably stress." You are frustrated but polite.

IDENTITY / OPENING

Sighs "Thank you for seeing me, Doctor. I've been going back and forth between different hospitals for almost two years now. I was told it's anxiety, then maybe my blood pressure, then Meniere's disease - but nothing they gave me really helped. I'm a teacher, I'm 44 years old, and honestly I'm just tired of not getting answers. My left ear..." pauses "...my RIGHT ear has been... not right... for a long time."

CHIEF COMPLAINT (when asked to describe the main problem)

"It started with ringing in my right ear. Then I noticed I wasn't hearing well on that side - especially on the phone. I'd hold it to my left ear automatically. Then the dizziness started."

HISTORY OF PRESENTING ILLNESS

"The ringing - the tinnitus - probably two and a half, maybe three years ago. I ignored it, thought it was nothing."

"It's constant. High-pitched. Only in the right ear. It doesn't come and go like waves - it's always there, always the same pitch. It never goes away completely."

"No. That's what puzzles me. It just... gradually got worse. One day I realized I couldn't really follow conversations in a noisy room if people were on my right side. It didn't suddenly drop or come back. It just kept slowly getting worse."

"It's not the room spinning like everyone says. It's more like... I feel off-balance. Unsteady, especially in the dark or when I close my eyes in the shower. Sometimes when I walk, particularly on uneven ground, I feel like I might drift to one side. But I don't get sudden attacks of spinning where I have to grab the wall. It's more like I've lost my sea legs."

"Mild nausea sometimes when I'm very unsteady. But I've never vomited or been bedridden from it. Nothing dramatic."

"Now that you mention it... yes. In the last maybe six months, the right side of my face sometimes feels slightly numb. Like when the dentist's anaesthesia is wearing off. I thought maybe I was sleeping on that side too much."

"No. The face moves normally, I think. My smile looks the same."

"I've had some headaches over the past few months. At the back of my head and neck, sort of a pressure feeling. Not like a migraine. Worse when I lean forward or strain."

"No, Doctor."

"Hmm... now that you ask, sometimes things seem a bit blurry when I move my head quickly. But it clears immediately. I never thought it was related."

PAST MEDICAL HISTORY

"I have mild hypertension, well controlled on amlodipine. I'm not diabetic. I had an ear infection when I was a teenager but nothing major since."

"A caesarean section 12 years ago. Nothing involving the ears or head."

"I had a CT scan two years ago at the government hospital. They said it was 'normal.' I also had audiometry done - the hearing test - and they told me there was some hearing loss in the right ear but they said it could just be age-related or noise exposure."

PAST DRUG AND ALLERGY HISTORY

"Amlodipine 5mg once daily. I was given betahistine for the Meniere's diagnosis but I stopped it because it wasn't helping at all."

"None that I know of."

FAMILY HISTORY

"My mother had... hmm... I think they said it was a brain tumour. She was operated in her 30s. She also had some skin lumps. She passed away some years ago. I'm not sure of the exact diagnosis."

"I have one brother. He's 38. Funnily enough, he complained last year about ringing in his ears. He hasn't been checked properly."

SOCIAL HISTORY

"I'm a secondary school teacher. Classroom environment, no industrial noise. No concerts, no heavy equipment use."

"I don't smoke. I drink socially, maybe one or two glasses of wine at weekends."

"No long trips."

"Significantly. I can't use the phone on my right side. I've had to rearrange my classroom so students sit on my left. I've stopped driving at night because the disorientation in the dark frightens me. I've had two sick days this term. And honestly... I've been quite anxious and low in mood about all this, which is why one of the doctors thought it was anxiety. But I know my own body - something is wrong."

SEXUAL AND REPRODUCTIVE HISTORY

"I'm married, yes. I'm on no oral contraceptive. I haven't started menopause yet - my periods are regular."

REVIEW OF SYSTEMS (Actor answers these as a prompt from the doctors)

EXAMINATION FINDINGS (Facilitator reads these out when audience asks to examine)

Vital Signs

• BP: 132/84, HR 76 regular, RR 16, SpO2 99%, Afebrile

General: Well-groomed, mildly anxious woman, no dysmorphic features. BMI 24.

Cranial Nerve Examination

TRAP for the audience: In SNHL, Rinne is AC > BC (positive Rinne - air conduction better than bone). The actor/facilitator should ask the audience what they find. If they say "negative Rinne on the right = conductive hearing loss," challenge them. The correct finding in SNHL is positive Rinne on the affected side (AC > BC) because both are reduced but AC remains relatively better. Weber lateralises to the OPPOSITE (better) ear in SNHL. This is a classic examination MCQ and OSCE trap.

Head Impulse Test (HIT/Halmagyi-Curthoys Test)

• Positive on the RIGHT: corrective saccade seen when head is thrust rapidly to the right.
• This indicates failure of the right vestibulo-ocular reflex (VOR) - a peripheral vestibular lesion on the right.

Romberg Test

• Stands with feet together, eyes open: stable
• Eyes closed: sways and falls to the right

Unterberger/Fukuda Stepping Test

• Marches on the spot with eyes closed: rotates to the right (towards the lesion)

Cerebellar Examination

• Mild right-sided dysmetria on finger-nose testing and heel-shin testing (cerebellar compression by the tumour)
• Gait: wide-based, slightly unsteady, no frank ataxia

Otoscopy

• Tympanic membranes: Bilateral normal appearance. No effusion, no perforation.

Skin

• Two small, firm, non-tender subcutaneous nodules palpable over the right paraspinal area and left forearm.

INVESTIGATIONS DISCUSSION (Audience Should Request These)

What the audience should ask for (prompt if they don't):

• Expected: Right-sided sensorineural hearing loss, worse at high frequencies. Speech discrimination score disproportionately poor compared to pure tone average (rollover phenomenon). This is a red flag for retrocochlear pathology.

• Expected: Prolonged wave I-III and I-V interpeak latency on the right (delay in neural transmission along the 8th nerve and brainstem). This is the classic electrophysiological signature of acoustic neuroma.

• Expected: "Ice cream cone" shaped enhancing mass in the right internal auditory canal extending into the CPA cistern. Widening of the IAC porus acusticus on the affected side. The tumour is heterogeneously enhancing, T1 isointense, T2 hyperintense. No hydrocephalus at this stage (tumour is ~2.8 cm).

• May show widening/erosion of the right internal auditory canal. Misses small tumours.

• Given the family history, test for NF2 gene mutation (chromosome 22q12). If confirmed, screen the brother.

• To look for posterior subcapsular cataracts (a feature of NF2 in young patients) and papilloedema.

DIAGNOSIS REVEAL

Diagnosis: Right-sided Vestibular Schwannoma (Acoustic Neuroma) in the context of Neurofibromatosis Type 2 (NF2)

Why tricky?

• 2.5-year diagnostic delay in the case
• Misdiagnosed as Meniere's disease, then anxiety
• CT was falsely reassuring - tumour was intracanalicular initially
• Family history (NF2) only revealed on targeted questioning
• Hearing loss is unilateral and progressive, not episodic - key differentiator
• CN V involvement (facial numbness) is a late sign that points away from Meniere's
• Physical signs require specific tests (HIT, Romberg) that are easy to forget

PATHOPHYSIOLOGY TEACHING POINTS

Origin

Why does it cause SNHL if it's on the vestibular nerve?

Why is facial nerve (CN VII) spared early?

Why does CN V get involved?

Histology

• Antoni A: Dense fibrillary spindle cells in palisading rows (Verocay bodies)
• Antoni B: Loose, myxoid, hypocellular stroma

NF2

• Autosomal dominant, chromosome 22q12, loss of merlin (schwannomin) tumour suppressor protein
• Hallmark: bilateral vestibular schwannomas (pathognomonic)
• Also: meningiomas, ependymomas, posterior subcapsular cataracts, skin schwannomas/plaques
• Presents before age 21 in classic cases; can be later with incomplete penetrance

TREATMENT DISCUSSION

Three options - tailor to tumour size, age, hearing status:

For THIS case (NF2, 2.8cm, still has serviceable hearing):

DISCUSSION QUESTIONS FOR THE AUDIENCE

1. What is the single most important imaging investigation and why does CT fail here?
2. How do you clinically differentiate vestibular schwannoma from Meniere's disease at the bedside?
3. What is the significance of the family history and what screening does it trigger?
4. Why does the facial nerve survive early in the disease course?
5. If this were a bilateral vestibular schwannoma in a 22-year-old - what diagnosis must you consider?
6. What does a positive Head Impulse Test tell you, and where is the lesion?
7. The audiogram showed rollover phenomenon - what is this and what does it mean?
8. The patient asks: "Doctor, will I go deaf?" - How do you counsel her?

FACILITATOR TIPS

• Don't let them ask leading questions. If someone says "do you have any numbness?" before examining the cranial nerves, just note it.
• The CT was normal - drive this point home. CT scanning intracanalicular tumours is notoriously insensitive. The answer is MRI with gadolinium.
• Time the case: History should take 15 minutes, examination findings 10 minutes, investigations discussion 10 minutes, diagnosis + pathophysiology 15 minutes, treatment 10 minutes.
• Throw a curveball at the end: "The MRI shows a second enhancing lesion along the left jugular foramen" - now ask the audience: does this change the diagnosis? (Yes - now NF2 is almost certain. Could be a meningioma or contralateral schwannoma.)
• The skin lumps will be missed by 90% of the audience. Plant them in the examination and see who picks it up.

The Case That Breaks Everyone

Why Cavernous Sinus Syndrome is the Perfect CBL Pick

• The MRI can be normal or show non-specific enhancement - and even when it's abnormal, the same finding looks identical in: meningioma, metastasis, lymphoma, Tolosa-Hunt, IgG4 disease, mucormycosis, and sarcoid
• The definitive test changes depending on which diagnosis you're chasing
• Steroids can help AND harm - if you give them empirically and it responds, was it Tolosa-Hunt, or did you just suppress a lymphoma temporarily?
• The audience will want to "MRI it and be done" - but then you show them the MRI report says "non-specific enhancing lesion in the left cavernous sinus - differential includes inflammatory vs. neoplastic process, clinical correlation recommended" - and watch their faces

CBL Script: "The Eye That Wouldn't Move"

Diagnosis: Cavernous Sinus Syndrome secondary to IgG4-Related Disease (masquerading as Tolosa-Hunt, then lymphoma, then meningioma)

• Rare enough that medical students won't name it in the first round
• Mimics every other cavernous sinus diagnosis on imaging
• Responds to steroids (so the "let's just give steroids and see" crowd gets briefly vindicated then has to think harder)
• Increasingly recognized, clinically relevant, and genuinely interesting
• Tissue biopsy is required for diagnosis - imaging alone cannot confirm it

PATIENT SCRIPT

Character: Mr. Haruto Mensah, 52M, Accountant

Actor instructions: You are an accountant. You are precise, analytical, and mildly obsessive about details - it's part of your character. You have been to an ophthalmologist, then a GP, and now a neurology team. You've been told it might be a blood clot in a vein behind your eye, then possibly a tumour, then possibly inflammation. You are visibly worried but composed. You keep trying to figure out the logic of your symptoms yourself, which is annoying but endearing. Your left eye has been the problem. You do NOT volunteer information unless directly asked. Make the doctors work for it.

IDENTIFICATION

CHIEF COMPLAINT

"My left eye. Something is wrong with it. It started with pain - and then it wouldn't move properly. I thought I was having a stroke at first."

HISTORY OF PRESENTING ILLNESS

"About six weeks ago. First there was pain. Just behind the left eye - deep, boring, constant. Not like a headache I'd normally get. More like pressure from the inside, like something is sitting behind the eye and pushing outward. I'd rate it maybe six out of ten at rest, going to eight if I try to move the eye to the left."

"It built up over three to four days. It wasn't there one morning and then - in stages - it got worse. I thought it was a sinus infection at first."

"About five days into it, I noticed double vision. When I looked to the left, I was seeing two images side by side - horizontally. I thought I was tired. Then it didn't go away. That's when I went to the ophthalmologist."

"Initially just to the left. But in the last two weeks, it's been worse. Now my eye doesn't seem to close all the way when I look to the upper left - and I have some double vision looking straight ahead too."

"She said my eye wasn't moving fully to the left, and there was some problem with the upper movement too. She was worried and sent me to you. She also mentioned my pupil on that side looked... larger? Or smaller? I can't remember."

"There is some redness - the white of the left eye looks a bit pink. And yes, actually... the left eye seems to sit slightly more forward than the right. My wife noticed it before I did."

"The left upper eyelid - yes, it's been a bit heavy. Droopy. Like when you're very tired."

"Yes - around the left eye and left side of the forehead. A bit numb. Like the area is wrapped in cotton wool. I can feel touch but it's dulled."

"The cheek I'm not sure - maybe a little. Lower jaw is fine."

"No fever that I've noticed. I haven't been sick. No dental work recently. I did have a sinus infection about three months ago but it cleared up with antibiotics. I didn't think it was related."

"My vision in that eye has been slightly blurry, but I thought it was because the eye keeps moving wrong. No darkness or patches I'd say."

"No, my face is symmetric. I can close both eyes and smile normally."

"No."

"No... wait. Actually, sometimes when it's very quiet at night I can hear a faint humming from the left side. Near the ear. I assumed it was tinnitus."

PAST MEDICAL HISTORY

"I was told I have type 2 diabetes about four years ago. Well controlled - my last HbA1c was 6.8%. I also have mild hypertension - on ramipril. Nothing else I know of."

"I wear reading glasses, just for presbyopia. No other eye history."

"No."

"No formal diagnosis. But I have had... recurrent episodes of dry eyes and dry mouth for the past couple of years. I mentioned it to my GP who said 'probably just age' and didn't investigate further."

"You know... yes. I had some swelling under my jaw on both sides about a year ago. It came and went. My GP said it might be a salivary gland stone but imaging at the time was normal. It's mostly resolved now."

PAST DRUG AND ALLERGY HISTORY

"Ramipril 5mg once daily. Metformin 1g twice daily. No supplements."

"Penicillin - rash. I carry a card."

FAMILY HISTORY

"My father had bowel cancer. Mother has rheumatoid arthritis. No eye problems in the family that I know of."

SOCIAL HISTORY

"I've never smoked. I drink socially - maybe three to four units a week."

"Office work only. No unusual exposures."

"I visited family in Ghana about eight months ago. About two weeks. No illness during the trip."

SEXUAL HISTORY

"I've been in a monogamous marriage for 24 years. I have not had any STI testing recently."

REVIEW OF SYSTEMS TABLE (for actor to use when students ask systems review)

PHYSICAL EXAMINATION FINDINGS

Vital Signs

• BP 138/88, HR 82 regular, T 37.1°C, RR 16, SpO2 98%

General

• Well-dressed, mildly anxious, no obvious cachexia. BMI 28.

Cranial Nerves - the core of the case

Horner vs CN III ptosis: Ask the audience to differentiate. CN III ptosis = complete/subtotal, pupil dilated. Horner = partial ptosis, pupil miotic (small), lower lid elevation, anhidrosis. In this case it's CN III. A Horner might coexist if sympathetics are also damaged but is harder to appreciate alongside a dilated CN III pupil.

Ocular bruit

• Auscultation over the closed left eye: soft systolic bruit audible. (This is a carotid-cavernous fistula sign - if students don't ask for it, the facilitator should ask "does anyone want to listen to anything?")

TWIST: The bruit is present but soft and low-grade. This does NOT confirm CCF - it narrows the DDx but doesn't close it. A CCF would classically have a loud bruit + pulsating exophthalmos + marked conjunctival engorgement. This is subtle.

Other Examination

• Left supraclavicular firm, non-tender, 1.5cm lymph node (students who asked about the "collarbone lump" in history will find it on examination - classic IgG4 lymphadenopathy)
• Salivary glands: mildly enlarged bilateral submandibular glands, non-tender, rubbery
• Chest, heart, abdomen: unremarkable
• No skin rash, no joint swelling

INVESTIGATIONS - THE JOURNEY (This is where the case comes alive)

Round 1: What does the audience order first?

Round 2: Imaging

"Enhancing soft tissue mass in the left cavernous sinus, extending to the superior orbital fissure. Left cavernous sinus is mildly expanded. No obvious internal carotid artery encasement or thrombosis. No frank bone destruction. Enhancement pattern is homogeneous. Differential diagnosis includes: inflammatory process (Tolosa-Hunt syndrome, IgG4-related disease, sarcoidosis), meningioma, lymphoma, or metastatic disease. Clinical correlation is recommended. MR angiography: no definite carotid-cavernous fistula identified on MRA, though a small dural AV fistula cannot be excluded."

1. This needs tissue - we can't diagnose from MRI alone
2. We need to rule out lymphoma and metastasis before giving steroids
3. We need to look for systemic disease
4. Serum IgG4, chest CT, and a biopsy plan should be the next steps

"Should we try steroids? If it responds it's Tolosa-Hunt."

Round 3: Further Workup

Round 4: The Tissue Question

Cavernous sinus biopsy is technically feasible but high risk (CN III, IV, VI, ICA all in the way). Best practice: biopsy the most accessible involved site - in this case, the enlarged left submandibular gland or a hilar lymph node via bronchoscopy/EBUS.

"Dense lymphoplasmacytic infiltrate with storiform fibrosis. Immunohistochemistry shows IgG4:IgG plasma cell ratio >40% and IgG4+ plasma cells >10/HPF. Features consistent with IgG4-related disease."

DIAGNOSIS REVEAL

Final Diagnosis: Cavernous Sinus Syndrome secondary to IgG4-Related Disease (IgG4-RD) with multi-organ involvement (cavernous sinus, submandibular glands, mediastinal nodes, periaortic region, kidneys)

PATHOPHYSIOLOGY TEACHING POINTS

Anatomy of the Cavernous Sinus - Localization in Clinical Neurology, 8e

Why CN VI goes first in many cavernous sinus lesions:

IgG4-Related Disease:

• A fibro-inflammatory condition characterised by tumour-like masses in multiple organs
• Histology: dense lymphoplasmacytic infiltrate rich in IgG4+ plasma cells, storiform fibrosis, obliterative phlebitis
• Serum IgG4 elevated in ~70% (NOT pathognomonic - elevated in many conditions, but >4x normal is highly suggestive)
• Classic sites: salivary glands (Mikulicz disease), pancreas (autoimmune pancreatitis type 1), retroperitoneum, kidneys, orbits, meninges, cavernous sinus
• Responds dramatically to steroids - but tissue diagnosis before steroids is best practice

The Pupil Rule:

• Compressive CN III palsy (aneurysm, tumour, IgG4 mass): pupil DILATED, poorly reactive. Parasympathetic fibres are on the outside of CN III - compressed first by external mass.
• Microvascular CN III palsy (diabetes, hypertension): pupil SPARED. Ischaemia damages the interior of the nerve (motor fibres) more than the surface (parasympathetic). - Adams & Victor, p.289

TREATMENT DISCUSSION

IgG4-RD:

If you had given steroids empirically before biopsy and the patient improved:

DISCUSSION QUESTIONS

1. Why is an isolated CN VI palsy in a diabetic patient different from multiple CN palsies with pain and proptosis in the same patient?
2. What is the anatomical reason CN VII is never involved in cavernous sinus syndrome?
3. The MRI shows enhancement in the cavernous sinus. List five diagnoses you cannot rule out from that finding alone. What single investigation would most change your next step?
4. The registrar wants to give steroids immediately because the patient is in pain. What is your argument for biopsy first?
5. A soft bruit is heard over the closed left eye. What does this suggest and how would you investigate it?
6. The serum IgG4 is elevated. A colleague says "that confirms IgG4-RD, no biopsy needed." Do you agree?
7. What non-neurological complications of IgG4-RD could this patient develop if untreated?
8. Why does the pupil become dilated in a compressive CN III palsy but not in a diabetic one?

FACILITATOR CHEAT SHEET: The Traps