Clarifying the Premise

Why the Brain Itself Feels No Pain

What is Awake Craniotomy?

• Speech and language (Broca's and Wernicke's areas, usually left hemisphere)
• Motor function (primary motor cortex)
• Sensory function (primary sensory cortex)
• Memory (mesial temporal structures)

"Awake craniotomy allows for speech, motor, or sensory cortical mapping in real time, hence facilitating a more aggressive resection of the tumor and minimizing risk to function."

• Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e

"Awake craniotomies are performed when tumors or epileptic foci lie close to cortical areas required for either speech or motor function, or to mesial-temporal structures critical to short-term memory."

• Miller's Anesthesia, 10e

How is the Patient Managed (If Not Under GA)?

1. Scalp Nerve Block / Field Block

• Supratrochlear nerve
• Supraorbital nerve
• Zygomaticotemporal nerve
• Auriculotemporal nerve
• Lesser occipital nerve
• Greater occipital nerve

2. Sedation Techniques

3. Intraoperative Cortical Mapping

Conditions Treated with Awake Craniotomy

• Brain tumours near eloquent cortex (especially gliomas)
• Epilepsy surgery (resection of seizure foci in temporal lobe)
• Arteriovenous malformations near speech/motor areas

Complications to Watch For

• Disinhibited or uncooperative patient
• Oversedation (unable to complete neuropsychological testing)
• Respiratory depression / airway obstruction
• Intractable brain oedema
• Intraoperative seizures - treated with cold saline poured on the cortex + small bolus of propofol (20 mg IV)
• Uncontrollable pain

Key Takeaway

How to Read a PET Scan Image

1. What a PET Scan Actually Measures

1. FDG is injected intravenously
2. Cells with high glucose demand (cancer, inflammation, active brain, heart) absorb more FDG
3. Unlike real glucose, FDG gets trapped inside the cell after phosphorylation - it cannot be metabolised further
4. Trapped FDG emits positrons, which produce pairs of gamma rays detected by the scanner
5. A 3D map of metabolic activity is reconstructed

"FDG competes with glucose for transport into the cell and for enzymatic phosphorylation by hexokinase. Unlike glucose, once phosphorylated to FDG-6-phosphate, it does not undergo further metabolism and is trapped inside the cell."

• Fishman's Pulmonary Diseases and Disorders

2. The Colour Scale (Colour Map)

3. The SUV - The Most Important Number

SUV = Tracer uptake in region (MBq/mL) ÷ [Administered activity (MBq) / Body weight (kg)]

• SUV < 2.5 - generally considered benign (e.g. pulmonary nodule)
• SUV 2.5 - 4 - equivocal, needs clinical correlation
• SUV > 4-5 - suspicious for malignancy in most contexts
• SUV of lymphoma, aggressive cancers - can exceed 10-20

4. PET/CT - Reading the Fusion

• PET alone shows WHERE metabolic activity is (but the anatomy is blurry)
• CT shows the precise anatomical structure
• Fused PET/CT tells you BOTH what is metabolically active AND exactly where it is

5. Normal (Physiologic) Uptake - Do NOT Mistake These for Disease

"Physiologic uptake of FDG is prevalent in the head and neck, especially during contraction of muscles (e.g., neck and thyroarytenoid muscles), and it may therefore be confused with tumor uptake."

• Cummings Otolaryngology Head and Neck Surgery

6. Causes of False Positives and False Negatives

False Positives (uptake that is NOT cancer):

• Infection / abscess - inflammatory cells have the same high glucose metabolism as cancer
• Post-surgical inflammation - scan should not be done until 8+ weeks after therapy
• Benign tumours (e.g. brown fat, sarcoidosis, thyroid disease)
• Muscle activity - patient was moving/tense during scan

False Negatives (cancer that is NOT seen):

• Hyperglycemia - high blood glucose competes with FDG for uptake, reducing signal (this is why patients must fast 4-6 hours before the scan)
• Well-differentiated / low-grade tumours - less metabolically active (e.g. mucinous CRC, some prostate cancers)
• Small lesions < 10 mm - below resolution threshold
• Slowly growing tumours (carcinoid, some thyroid cancers)

7. Key Advanced Metrics

8. Common Non-FDG Tracers (Beyond Glucose)

Summary

1. Identify hot spots - any focal area of increased uptake beyond background
2. Decide if it is physiologic or pathologic - know your normal structures
3. Quantify with SUV - number gives you an objective measure of metabolic intensity

• Sources: Fishman's Pulmonary Diseases and Disorders, Cummings Otolaryngology Head and Neck Surgery, Scott-Brown's Otorhinolaryngology, Current Surgical Therapy 14e, Grainger & Allison's Diagnostic Radiology

Ga-68 PSMA PET/CT Full Body Scan: Complete Reading Guide with Bony Metastasis

1. What is PSMA and Why it Works

• Binds directly to cancer cells (not just bone reaction like a bone scan)
• Rapid clearance from non-target tissue = high tumour-to-background contrast
• Works even at very low PSA levels (detects disease where conventional imaging cannot)
• Now FDA approved for intermediate- and high-risk prostate cancer staging and biochemical recurrence

"68Ga-PSMA PET scans have shown promise in identifying nodal and bone metastasis that would have otherwise been missed with conventional CT scans."

• Smith and Tanagho's General Urology, 19e

"This scan is now FDA approved for patients with intermediate- and high-risk prostate cancer and is substantially more sensitive and accurate in the detection of metastases compared to conventional imaging."

• Harrison's Principles of Internal Medicine, 22e

2. Normal Physiologic Uptake on Ga-68 PSMA (What You Expect to See)

3. How to Read the MIP (Maximum Intensity Projection) - The First View

1. Orient yourself - identify salivary glands (top), liver/spleen (mid-abdomen), kidneys (flanks), bladder (pelvis)
2. Scan top to bottom - skull, cervical spine, thorax/ribs, thoracic spine, lumbar spine, pelvis, femora
3. Mark any hot spot outside of expected physiologic uptake
4. Note symmetry - bilateral symmetric uptake = usually benign; asymmetric focal = suspicious
5. Fuse with CT - every suspicious PET finding must be localised on CT to confirm bony vs. soft tissue

4. Distribution of Bone Metastases on PSMA PET

Where Bone Metastases Appear - in Order of Frequency

What a Bone Metastasis Looks Like

• On MIP: A focal dark spot (greyscale inversion - hot = dark on standard PSMA display) outside of normal physiologic sites
• On PET axial slice: Focal intense PSMA uptake
• On fused PET/CT: The PET hot spot colocalises with either:
  • A sclerotic lesion on CT (blastic met - white on CT)
  • A lytic lesion on CT (dark/destructive on CT)
  • No visible CT change (early micrometastasis - PSMA detects before CT changes occur)

PSMA detects bone metastases by targeting the cancer cells directly, not the bone reaction. This is why it detects early lesions that are invisible to conventional bone scan.

5. PSA Level and Bone Metastasis Detection Rate

6. Interpreting the Bone Lesion - What to Report

Oligometastatic vs. Widespread Disease - Clinical Significance

7. PSMA vs. Conventional Bone Scan - Head-to-Head

• Bone scan detects osteoblastic reaction (indirect signal) - misses early lesions and lytic metastases
• PSMA PET detects cancer cells directly - positive even before bone reaction starts
• Bone scan cannot detect nodal or visceral disease simultaneously
• PSMA PET is a whole-body staging tool in one examination

8. Pitfalls and False Positives to Know

9. Theranostics - PSMA as Treatment

• 177Lu-PSMA-617 (Lutetium-177) - beta emitter for treatment of metastatic CRPC
• 225Ac-PSMA (Actinium-225) - alpha emitter for more resistant disease

"A targeted radio-ligand therapy, 177Lu-PSMA-617, targets prostate-specific membrane antigen, which is highly expressed in prostate cancer, as demonstrated by a positive prostate-specific membrane antigen PET."

• Goldman-Cecil Medicine

10. Reporting Checklist for a Full Body Ga-68 PSMA Scan

• PSMA-avid lesion in prostate/bed? SUVmax?

• Pelvic nodes (internal iliac, external iliac, obturator, presacral)
• Para-aortic / retroperitoneal nodes
• Mediastinal / supraclavicular nodes

• Skull and calvarium
• Cervical spine (C1-C7)
• Thoracic spine (T1-T12)
• Ribs and sternum, clavicles
• Lumbar spine (L1-L5)
• Sacrum and pelvis (iliac wings, acetabulum, pubis, ischium)
• Proximal femora and humeri
• Distal long bones (if total-body FOV)

• Liver, lung, adrenal lesions

T12 Metastasis with SUVmax 18 on Ga-68 PSMA PET - Full Interpretation

What This Finding Means

SUVmax of 18 - How Significant Is It?

PSMA is expressed 100-1000 fold higher in prostate cancer cells vs. normal tissue, giving very high lesion-to-background ratios. An SUVmax of 18 far exceeds physiologic background at any spinal level.

Why T12 Specifically Matters

"The thoracic spinal column is most commonly involved... Prostate and ovarian cancers occur disproportionately in the sacral and lumbar vertebrae, probably from spread through Batson's plexus, a network of veins along the anterior epidural space."

• Harrison's Principles of Internal Medicine, 22e

What to Look for on the Fused CT at T12

Urgent Red Flags to Assess Clinically

• Back pain at T12 level (worse at night, with coughing/movement)
• Bilateral leg weakness or heaviness
• Numbness / tingling in lower limbs or saddle area
• Bowel or bladder dysfunction (conus = early sphincter involvement)

"Pain is usually the initial symptom of spinal metastasis; it may be aching and localized or sharp and radiating... A recent onset of persistent back pain, particularly if in the thoracic spine (which is uncommonly involved by spondylosis), should prompt consideration of vertebral metastasis."

• Harrison's Principles of Internal Medicine, 22e

"Up to 40% of patients who present with cord compression at one level are found to have asymptomatic epidural metastases elsewhere - imaging of the entire length of the spine is important."

• Harrison's Principles of Internal Medicine, 22e

Mandatory Next Step: MRI Spine

• Epidural extension (tumour pushing into the spinal canal)
• Degree of cord compression if any
• Vertebral height and structural integrity
• Other unsuspected vertebral lesions not yet causing bone reaction

Clinical Management Pathway for T12 Met (SUVmax 18)

If This is the ONLY Bone Lesion (Oligometastatic)

"Stereotactic body radiotherapy, which delivers high doses of focused radiation, is preferred for radioresistant tumor types and for patients requiring re-irradiation."

• Harrison's Principles of Internal Medicine, 22e

If Multiple Bone Lesions (Polymetastatic)

If Cord Compression Signs Present

1. Dexamethasone 10 mg IV immediately - reduces cord oedema
2. Maintain on dexamethasone 4 mg every 6 hours orally
3. Urgent MRI whole spine - same day
4. Urgent surgical/neurosurgical review - decompression if indicated
5. Radiotherapy as definitive treatment post-surgery or as primary treatment

"Motor deficits (paraplegia or quadriplegia), once established for >12 h, do not usually improve, and beyond 48 h, the prognosis for substantial motor recovery is poor."

• Harrison's Principles of Internal Medicine, 22e

Summary Box

Suture Choice for Sharp Laceration Over the Anterior Leg

Why the Anterior Leg is a Special Problem

• Skin here is thin, tightly adherent, with minimal subcutaneous fat
• Sits directly over the tibia with almost no subcutaneous cushion
• Blood supply is poor - the skin is a watershed zone
• Particularly in elderly patients, the skin is extremely fragile and tears easily around sutures
• High tension on wound edges (from oedema, dependent swelling)
• Healing is slow - on average 60 days even with good closure

1. Minimally reactive (to avoid inflammatory breakdown)
2. Non-cutting (monofilament preferred over braided to reduce drag)
3. Tension-distributed (suture technique matters as much as material)

Recommended Suture: 3-0 or 4-0 Nylon (Monofilament Non-Absorbable)

First Choice: Monofilament Nylon (Ethilon / Dermalon)

"Nylon: General surgical use - skin closure, abdominal wall mass closure, hernia repair, plastic surgery, neurosurgery, microsurgery, ophthalmic surgery. Contraindications: None."

• Bailey and Love's Short Practice of Surgery, 28e

Second Choice: Polypropylene (Prolene / Surgipro)

What NOT to Use on the Anterior Leg

Suture Size Guide for the Anterior Leg

"The distance of insertion from the edge of the wound should correspond to the thickness of the tissue being sutured. Each successive suture should be placed at twice this distance apart."

• Bailey and Love's Short Practice of Surgery, 28e

Best Technique: Simple Interrupted Sutures

• If one suture cuts through the fragile skin, the entire closure does not fail
• Allows wound inspection between sutures
• Can be selectively removed if infection develops

• Place sutures 5-8 mm apart and 5 mm from wound edge (adjust for tissue thickness)
• Do not tie too tightly - oedema will cause sutures to cut through if overtightened at the time of placement

Alternative Technique: Vertical Mattress Suture

• Evert the wound edges (reduces dead space)
• Distribute tension over a wider area (critical in thin pretibial skin)
• Prevent skin edge inversion which causes poor healing

"Mattress sutures... are very useful in producing an accurate approximation of wound edges, especially when the edges to be anastomosed are irregular in depth or disposition."

• Bailey and Love's Short Practice of Surgery, 28e

Deep Layer (If Wound is Deep)

• Use 3-0 Vicryl (polyglactin 910) as a buried absorbable deep layer first
• This reduces wound tension on the skin edges before nylon skin closure
• Vicryl retains ~60% tensile strength at 2 weeks, ~30% at 3 weeks

When NOT to Close Primarily (Important!)

• Wound is contaminated or > 6-8 hours old (risk of infection)
• Skin flap is ischaemic or purple/congested - primary closure will necrose
• Elderly/fragile skin with large flap - tension closure risks total flap loss

Summary Recommendation

Lab Report Interpretation - Mr. Dhaval Dama, Male, 28 Years

The Two Key Findings at a Glance

Understanding Each Finding

1. Elevated AEC = 1388 /cmm

• Parasitic (helminth) infections
• Allergic/atopic conditions
• Certain drugs and autoimmune conditions

"Eosinophilia is present if blood eosinophils exceed ~0.35-0.5 × 10⁹/L. Reactive eosinophilia is typically associated with allergic processes and parasitic infections."

• Henry's Clinical Diagnosis and Management by Laboratory Methods

2. Elevated Total IgE = >1000 IU/mL

• Mediates immediate hypersensitivity (Type I allergic) reactions
• Is produced in large quantities in response to helminthic parasites
• Triggers mast cell and basophil degranulation (allergic symptoms)

Why These Two Together Are Very Significant

"Moderate to severe peripheral eosinophilia is most commonly associated with infection by helminths, including nematodes, trematodes, and cestodes."

• Henry's Clinical Diagnosis and Management by Laboratory Methods

"Key causes of eosinophilia: Parasitic - trichinosis, filariasis, schistosomiasis; Allergic - urticaria, hay fever, asthma"

• Henry's Clinical Diagnosis (Box 34.4)

Differential Diagnosis - Most Likely to Least Likely

🔴 Most Likely: Parasitic (Helminthic) Infection

🟡 Also Consider: Allergic / Atopic Conditions

• Bronchial asthma (exogenous/allergic type)
• Allergic rhinitis / hay fever
• Atopic dermatitis / eczema
• Urticaria

🟢 Less Likely but Must Rule Out

• Drug reaction (check current medications)
• Hyper-IgE syndrome (Job's syndrome) - rare, would have recurrent skin abscesses + IgE usually >2000
• Hodgkin lymphoma (if constitutional symptoms present)
• Churg-Strauss syndrome / EGPA (if asthma + systemic features)

What Further Investigations to Order

First-Line (Essential - Order Now)

Second-Line (Based on Clinical Suspicion)

Treatment

Step 1 - Empirical Anthelmintic Therapy

• Effective against: roundworm, hookworm, whipworm, Strongyloides, Toxocara
• Repeat dose after 2 weeks for hookworm/strongyloides

• Ivermectin 200 mcg/kg single dose - especially if Strongyloides suspected (causes very high IgE)
• Diethylcarbamazine (DEC) 6 mg/kg/day × 12 days - if filariasis suspected

Step 2 - Treat Allergic Component (if present)

Step 3 - If No Parasites Found (After Thorough Workup)

• Allergist/Immunologist - for specific IgE testing and allergy management
• Haematologist - if AEC rises > 1500 or organ involvement suspected (Hypereosinophilic syndrome)

Patient Advice (What to Tell Mr. Dhaval Dama)

🔵 Lifestyle and Hygiene

1. Wash hands thoroughly before eating and after toilet
2. Wear footwear always outdoors - especially in soil/garden areas (prevents hookworm entry through feet)
3. Drink only boiled/filtered water - do not drink tap or well water directly
4. Avoid eating unwashed raw vegetables and undercooked meat
5. Deworm the entire household - all family members should take albendazole 400 mg single dose (as routine deworming)
6. Pet hygiene - if dogs/cats at home, deworm pets regularly; wash hands after contact

🔵 Diet

• No raw/undercooked pork or meat (Trichinella, Taenia risk)
• Avoid walking barefoot in soil (especially after rain)
• Wash fruits and vegetables with clean water before eating

🔵 Symptoms to Watch For (Return Immediately)

🔵 Follow-Up

• Repeat AEC in 4-6 weeks after treatment - should fall significantly if parasitic cause
• Repeat IgE in 3 months - will take longer to normalise
• Bring stool report to follow-up visit

Summary for Clinician