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PAPER II - RADIOLOGY UNIVERSITY EXAM - DETAILED ANSWERS

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QUESTION 1 (30 Marks)

Radiology of CNS Manifestations of HIV - MRI Findings with Differential Diagnosis

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INTRODUCTION

┌─────────────────────────────────────────────────────────────────────┐
│              CD4 COUNT AND CNS MANIFESTATIONS IN HIV                │
│                                                                     │
│  CD4 > 500     →  Aseptic meningitis, Guillain-Barré syndrome       │
│  CD4 200-500   →  TB meningitis, Herpes zoster                      │
│  CD4 < 200     →  Toxoplasmosis, Cryptococcus, PML                  │
│  CD4 < 100     →  CMV encephalitis, Cryptococcal meningitis         │
│  CD4 < 50      →  CNS Lymphoma (PCNSL), CMV, MAC                   │
└─────────────────────────────────────────────────────────────────────┘

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A. DIRECT HIV MANIFESTATIONS

1. HIV ENCEPHALITIS / HIV-Associated Dementia (HAND)

• T2/FLAIR: Bilateral, symmetric, confluent hyperintense signal in periventricular and subcortical white matter - "diffuse white matter disease"
• T1: Hypointense white matter changes
• DWI: No restriction (differentiates from PML)
• Contrast: No enhancement (blood-brain barrier intact)
• Atrophy: Cortical and subcortical atrophy, ventricular enlargement (HIV encephalopathy end-stage)
• Basal ganglia: T2 hyperintensity in basal ganglia and thalamus

• PML (more asymmetric, U-fiber involvement, subcortical)
• CMV encephalitis (periventricular enhancement)
• ADEM

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B. OPPORTUNISTIC INFECTIONS

2. CEREBRAL TOXOPLASMOSIS

• Concentric target sign: Multiple rings of alternating signal on T2 - central T2 hypointensity (haemorrhage/calcification), surrounded by T2 hyperintensity (necrosis), outer T2 hypointense wall, peripheral edema
• Eccentric target sign: Nodular enhancement within the ring on post-contrast T1
• Location: Predilection for basal ganglia, thalamus, corticomedullary junction
• Multiple lesions (> 80% bilateral), with edema and mass effect
• May show associated hemorrhage

DIAGRAM: Toxoplasmosis Lesion Layers (Concentric Target Sign)
┌─────────────────────────────────┐
│  Perilesional edema (T2 bright) │
│  ┌──────────────────────────┐   │
│  │  Enhancing ring wall     │   │
│  │  ┌────────────────────┐  │   │
│  │  │  T2 dark rim       │  │   │
│  │  │  ┌──────────────┐  │  │   │
│  │  │  │ Necrotic core│  │  │   │
│  │  │  │ T2 bright    │  │  │   │
│  │  │  └──────────────┘  │  │   │
│  │  └────────────────────┘  │   │
│  └──────────────────────────┘   │
└─────────────────────────────────┘

• PCNSL (primary CNS lymphoma) - usually solitary, periventricular, diffusion restriction
• TB abscess/tuberculoma
• Pyogenic abscess
• Glioblastoma
• Metastasis

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3. PRIMARY CNS LYMPHOMA (PCNSL)

• Usually solitary (unlike toxoplasmosis which is multiple)
• Periventricular location (corpus callosum, basal ganglia, ependyma)
• "Butterfly" pattern crossing corpus callosum
• Subependymal spread
• May show crossing of corpus callosum (like GBM)
• Thallium-201 SPECT: hot (useful to differentiate from toxoplasmosis which is cold)

• Toxoplasmosis (multiple, target sign, responds to anti-toxo treatment)
• Glioblastoma (older patients, cortical involvement)

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4. PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY (PML)

• Asymmetric, non-enhancing white matter lesions
• Scalloped margins following gyri (U-fiber involvement)
• Favors parieto-occipital and posterior fossa white matter
• No mass effect, no edema (distinguishes from PCNSL/toxo)
• PML-IRIS (immune reconstitution): lesions may transiently enhance after ART initiation

DIAGRAM: PML vs HIV Encephalitis White Matter Changes

PML:                          HIV Encephalitis:
  [Asymmetric]                  [Symmetric bilateral]
  [Subcortical U-fibers]        [Periventricular]
  [No enhancement]              [No enhancement]
  [Parieto-occipital]           [Diffuse]

• HIV encephalitis (bilateral symmetric, no U-fiber involvement)
• CMV encephalitis (periventricular enhancement)
• MS (smaller lesions, enhancing active plaques, periventricular/callosal)

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5. CRYPTOCOCCAL MENINGOENCEPHALITIS

• Gelatinous pseudocysts ("soap bubble" appearance) in perivascular spaces (Virchow-Robin spaces) - especially basal ganglia, thalamus
• Cryptococcomas: single/multiple parenchymal lesions with ring enhancement
• Communicating hydrocephalus (obstruction of CSF drainage)
• Dilated Virchow-Robin spaces filled with organisms
• Meningeal enhancement may be absent despite active infection

• Lacunar infarcts (smaller, DWI restriction acutely)
• Cysticercosis (perilesional edema, scolex on MRI)
• Dilated perivascular spaces (no enhancement)

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6. CMV ENCEPHALITIS

• T2/FLAIR: Periventricular hyperintensity - smooth rim of signal around ventricles
• T1+Gad: Periventricular enhancement (ependymitis)
• Subependymal enhancement
• Ependymitis pattern: irregular ventricular walls
• Diffuse encephalitis: bilateral white matter changes

• HIV encephalitis
• PML
• Periventricular metastases

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7. TUBERCULOUS MENINGITIS / TUBERCULOMA

• Meningitis: Basal cistern enhancement (basal exudate), communicating hydrocephalus
• Tuberculoma: Ring-enhancing lesion; T2 hypointense centre (caseating necrosis with calcification)
• MR spectroscopy: Lipid peak at 1.3 ppm
• Central calcification ("target" appearance on CT)
• Vasculitis: infarcts in lenticulostriate territory (internal capsule, basal ganglia)

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8. HIV MYELOPATHY (Vacuolar Myelopathy)

• MRI spine: T2 hyperintensity in posterior and lateral columns
• Thoracic cord most affected
• No enhancement
• DDx: Subacute combined degeneration (B12 deficiency), MS

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SUMMARY TABLE - CNS MANIFESTATIONS OF HIV

┌──────────────────┬──────────────────┬──────────────────────┬───────────────────────┐
│  Disease         │  CD4 Count       │  MRI Hallmark        │  Key DDx              │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  HIV Encepha-    │  Any (severe     │  Symmetric bilateral │  PML, ADEM            │
│  litis/HAND      │  < 200)          │  WM T2 signal, no    │                       │
│                  │                  │  enhancement         │                       │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  Toxoplasmosis   │  < 200           │  Multiple ring-      │  PCNSL, TB abscess    │
│                  │                  │  enhancing, BG;      │                       │
│                  │                  │  concentric target   │                       │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  PCNSL           │  < 50            │  Solitary, peri-     │  Toxoplasmosis        │
│                  │                  │  ventricular,        │  (empirical Rx trial) │
│                  │                  │  diffusion restrict. │                       │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  PML             │  < 200           │  Asymmetric WM,      │  HIV encephalitis     │
│                  │                  │  U-fibers, NO        │  MS                   │
│                  │                  │  enhancement         │                       │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  Cryptococcus    │  < 100           │  Gelatinous          │  Lacunar infarcts,    │
│                  │                  │  pseudocysts,        │  cysticercosis        │
│                  │                  │  dilated VR spaces   │                       │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  CMV             │  < 50            │  Periventricular     │  HIV encepha-         │
│                  │                  │  enhancement,        │  litis, PML           │
│                  │                  │  ependymitis         │                       │
├──────────────────┼──────────────────┼──────────────────────┼───────────────────────┤
│  TB              │  Any             │  Basal enhance-      │  Bacterial meningitis │
│                  │                  │  ment, ring-enhan.   │  Cryptococcus         │
│                  │                  │  T2-dark centre      │                       │
└──────────────────┴──────────────────┴──────────────────────┴───────────────────────┘

• Multiple lesions + BG location + fever → try 2-week anti-toxoplasmosis empirically
• If no improvement → biopsy → PCNSL
• Thallium-SPECT: PCNSL is "hot", Toxo is "cold"
• MRS: PCNSL shows elevated Cho, Toxo shows lipid/lactate peak
• DWI: PCNSL shows restricted diffusion centrally; Toxo shows peripheral restriction

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QUESTION 2 (30 Marks)

Pathophysiology of Hyperparathyroidism with Detailed Skeletal Manifestations

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ETIOLOGY AND CLASSIFICATION

Primary Hyperparathyroidism (PHPT):

• 80% - Solitary parathyroid adenoma
• 15-20% - Four-gland hyperplasia
• < 0.5% - Parathyroid carcinoma
• Associated with MEN1 (MEN1 gene), MEN2A (RET gene), CDC73 mutations

Secondary Hyperparathyroidism (SHPT):

• Chronic kidney disease (most common cause)
• Vitamin D deficiency
• Malabsorption

Tertiary Hyperparathyroidism:

• Autonomous PTH secretion in long-standing SHPT (post-renal transplant)

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PATHOPHYSIOLOGY

DIAGRAM: Pathophysiology of Hyperparathyroidism

TRIGGER (Adenoma/Hyperplasia/↓Ca²⁺ in SHPT)
                │
                ▼
       ↑↑ PTH Secretion
                │
     ┌──────────┼──────────────┐
     ▼          ▼              ▼
  BONE        KIDNEY         INTESTINE
     │          │              │
↑Osteoclast  ↑Ca²⁺ reabsorption  ↑Ca²⁺ absorption
 activity    ↓Phosphate        (via ↑1,25-OH-D)
↑RANKL       reabsorption
↓OPG         ↑1α-hydroxylase
     │          │              │
     ▼          ▼              ▼
↑Ca²⁺ from  ↑Urinary Ca²⁺   ↑Intestinal Ca²⁺
  bone       (hypercalciuria)  absorption
     │
     ▼
  SKELETAL MANIFESTATIONS

PTH Mechanism at Bone Level:

1. PTH binds PTH-R1 receptor on osteoblasts
2. Osteoblasts upregulate RANKL and downregulate Osteoprotegerin (OPG)
3. RANKL binds RANK on osteoclast precursors → osteoclast activation
4. Net result: bone resorption > bone formation
5. Cortical bone preferentially affected over trabecular bone (explains distal radius bone loss vs preserved lumbar spine in PHPT)

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SKELETAL MANIFESTATIONS - RADIOLOGICAL FINDINGS

The Classic Triad: "Stones, Bones, Groans" (bones component)

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1. SUBPERIOSTEAL BONE RESORPTION

• Loss of the smooth cortical outline
• "Lacy," "frayed," or "moth-eaten" periosteal margin
• Cortical tunneling
• Intracortical striations ("railroad track" appearance)

• Medial aspect of proximal tibia and femur
• Inferior surface of clavicle (distal tapering)
• Superior aspect of ribs (rib notching)
• Medial margin of scapula
• Lamina dura around teeth - loss of lamina dura (early sign)
• Sacroiliac joints (widening, erosion - "pseudo-widening")

DIAGRAM: Subperiosteal Resorption of Phalanges

Normal:           Hyperparathyroidism:
  ┌───┐              ┌─ ─┐
  │   │              │   │  ← irregular cortex
  │   │              │   │    (frayed/lacy)
  │   │              │   │
  └───┘              └─ ─┘
Smooth cortex     Subperiosteal resorption
                  on radial side

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2. OSTEITIS FIBROSA CYSTICA (OFC)

• Generalized cortical thinning
• Diffuse skeletal radiolucency ("ground glass" osteopenia)
• Cystic bone lesions (see Brown Tumors below)
• Bone deformities in severe/chronic cases

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3. BROWN TUMORS

• Well-defined, expansile, purely lytic lesion (eccentric or central)
• No periosteal reaction, no sclerotic margin
• Long bones (femur, radius, ulna), pelvis, mandible, clavicle, ribs
• May be multiple

• T1: Heterogeneous low signal
• T2: Heterogeneous (fluid levels in cysts)
• Variable contrast enhancement

• Giant cell tumor (epiphysis, younger patients, no HPT)
• Aneurysmal bone cyst (fluid-fluid levels, posterior spinal elements)
• Metastases (multiple, irregular margins, known primary)
• Multiple myeloma (diffuse, "punched out" lesions)

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4. SALT AND PEPPER SKULL

• Granular, "moth-eaten" or "salt and pepper" appearance of the skull vault
• Loss of distinction between inner and outer tables
• Seen on lateral skull X-ray
• Spares the skull base

DIAGRAM: Salt and Pepper Skull
┌─────────────────────────────────┐
│  ··  •  ·  ••  ·  •  ·  ·     │
│  ·  ••  ·  •  ··  •  ··  •  · │  ← Granular patchy
│  •  ·  ••  ·  •  ·  ••  ·  •  │    appearance
└─────────────────────────────────┘

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5. NEPHROCALCINOSIS / RENAL CALCULI (Radiological)

• Nephrolithiasis: Radio-opaque calcium oxalate/phosphate stones on KUB, IVU, CT (non-contrast CT is gold standard)
• Nephrocalcinosis: Diffuse calcium deposition in renal parenchyma - medullary (most common) pattern on ultrasound/KUB

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6. CHONDROCALCINOSIS

• X-ray: Linear calcification in fibrocartilage (knee menisci, symphysis pubis, triangular fibrocartilage of wrist)
• Due to calcium pyrophosphate deposition (CPPD)
• May cause acute pseudogout attacks
• Seen in both PHPT and SHPT

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7. PERIOSTEAL NEW BONE FORMATION / RUGGER JERSEY SPINE

• Rugger jersey spine: Dense bands of sclerosis at the superior and inferior endplates of vertebrae, with relative radiolucency in between
• Gives a "striped jersey" or "sandwich" vertebra appearance
• Due to alternating osteosclerosis (at endplates) and osteomalacia/resorption

DIAGRAM: Rugger Jersey Spine
┌─────────────────────┐
│ ████████████████████│ ← Dense sclerotic endplate
│                     │
│                     │ ← Normal/lucent centre
│                     │
│ ████████████████████│ ← Dense sclerotic endplate
│                     │
│                     │
│ ████████████████████│
└─────────────────────┘

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8. OSTEOPOROSIS / OSTEOPENIA

• Generalized reduction in bone mineral density
• Cortical bone > trabecular bone
• Distal 1/3 of radius most affected (purely cortical)
• Pathological fractures

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9. LOOSER ZONES (in secondary HPT with osteomalacia component)

• Lucent transverse bands perpendicular to the cortex (pseudofractures)
• Commonly at femoral neck, pubic rami, medial tibia, ribs
• Symmetric distribution

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SUMMARY TABLE - Skeletal Manifestations

┌───────────────────────────────┬──────────────────────────────────────────────┐
│  Finding                      │  Radiological Appearance                     │
├───────────────────────────────┼──────────────────────────────────────────────┤
│  Subperiosteal resorption     │  Frayed cortex on radial mid-phalanges        │
│  Brown Tumors                 │  Expansile lytic lesions, long bones/jaw      │
│  Salt and pepper skull        │  Granular skull vault, lateral X-ray          │
│  Osteitis fibrosa cystica     │  Diffuse radiolucency + cysts                 │
│  Rugger jersey spine          │  Endplate sclerosis (SHPT)                    │
│  Chondrocalcinosis            │  Cartilage calcification (CPPD)               │
│  Loss of lamina dura          │  Absent white line around tooth roots (early) │
│  Looser zones                 │  Pseudofractures (SHPT+osteomalacia)          │
│  Nephrocalcinosis             │  Medullary calcification on USS/KUB           │
└───────────────────────────────┴──────────────────────────────────────────────┘

---

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QUESTION 3 (2 x 10 Marks)

Q3 Part 1: CAROTID BODY TUMOUR (Chemodectoma / Paraganglioma)

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DEFINITION AND ANATOMY

EPIDEMIOLOGY

• More common at high altitudes (chronic hypoxia → carotid body hyperplasia)
• Peak: 5th decade
• 10% familial (SDH gene mutations - SDHB, SDHC, SDHD)
• Familial cases: association with phaeochromocytoma
• Bilateral in 5% (up to 30% in familial cases)
• Usually benign; < 5% malignant

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CLINICAL FEATURES

• Slowly enlarging, painless, pulsatile lump at the carotid bifurcation
• Mobile laterally but NOT vertically (Fontaine's test)
• Bruit may be present
• Can empty on pressure then slowly refill
• 1/3 present as parapharyngeal mass (pushing tonsil medially and anteriorly)
• Neural involvement: Horner's syndrome, hoarseness, dysphagia (cranial nerves IX-XII)
• FNAC and open biopsy are CONTRAINDICATED (highly vascular, risk of haemorrhage)

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CLASSIFICATION (Shamblin System)

┌─────────────────────────────────────────────────────────────┐
│  SHAMBLIN CLASSIFICATION                                     │
│                                                             │
│  Group I:   Small tumour, minimal carotid adherence         │
│             (easily resected)                               │
│                                                             │
│  Group II:  Tumour adherent to/partially surrounds carotids │
│             (moderate complexity)                           │
│                                                             │
│  Group III: Tumour encases ICA + ECA (>270 degrees)         │
│             (high complexity, vascular surgery required)    │
└─────────────────────────────────────────────────────────────┘

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RADIOLOGY

1. ULTRASOUND (First-line investigation)

• Hypoechoic solid vascular mass at carotid bifurcation
• Color Doppler: highly vascular with multiple internal flow signals
• Splaying of ICA and ECA seen on longitudinal scan
• Cannot assess deep extent

2. CT ANGIOGRAPHY (CTA)

• Investigation of choice for surgical planning
• Hypervascular, intensely enhancing mass at carotid bifurcation
• Characteristic splaying of ICA and ECA = "LYRE SIGN"
• Assesses degree of carotid encasement (Shamblin grading)
• 3D reconstruction shows full vascular relationships
• Identifies bilateral tumours
• May show internal cystic component (necrosis)

3. MRI / MRA

• T1: Iso to hypointense compared to muscle
• T2: Hyperintense; classic "salt and pepper" pattern
  • Multiple punctate areas of HIGH signal (slow flow in vascular channels = "salt")
  • Multiple punctate areas of LOW signal (signal voids = fast flow = "pepper")
• T1+Gad: Intense heterogeneous enhancement
• MRA: Demonstrates splaying of carotid bifurcation (Lyre sign)
• Defines parapharyngeal/skull base extension

DIAGRAM: LYRE SIGN (Splaying of Carotid Bifurcation)

       ICA     ECA
        ↑        ↑
        |        |
        |        |
     [TUMOUR fills
      the fork]
        |
       CCA

4. DIGITAL SUBTRACTION ANGIOGRAPHY (DSA)

• Historically the primary modality (now reserved for pre-op embolization)
• Shows:
  • Splaying of ICA and ECA (Lyre sign)
  • Intense tumour blush (hypervascular stain)
  • "Early vein" - arteriovenous shunting (early venous opacification)
  • Main blood supply via ascending pharyngeal artery
  • Carotid occlusion test (if ICA sacrifice considered)

5. RADIONUCLIDE SCAN

• Octreotide scan (somatostatin receptor scintigraphy): Positive uptake (paraganglioma cells express somatostatin receptors)
• MIBG scan: May be positive; useful to identify functional/multifocal tumours
• 68Ga-DOTATATE PET/CT: Best sensitivity for localising multiple/metastatic paragangliomas

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DIFFERENTIAL DIAGNOSIS

┌────────────────────────────────┬────────────────────────────────────────────┐
│  DDx                           │  Key Differentiating Feature               │
├────────────────────────────────┼────────────────────────────────────────────┤
│  Schwannoma (vagal/sympathetic)│  Displaces carotid anteriorly, no lyre sign│
│  Neurofibroma                  │  Anteromedial displacement, NF1 features   │
│  Branchial cleft cyst          │  Cystic, no vascularity, lateral to carotid│
│  Lymph node metastasis         │  Multiple, irregular, known primary        │
│  Glomus vagale                 │  Higher up, post-styloid, no bifurcation    │
│  Lymphoma                      │  Multiple, soft, no vascular blush         │
└────────────────────────────────┴────────────────────────────────────────────┘

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Q3 Part 2: CYSTIC LESIONS IN THE NECK

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CLASSIFICATION

DIAGRAM: Cystic Lesions of the Neck - Classification

                    CYSTIC NECK LESIONS
                           │
         ┌─────────────────┼──────────────────┐
         ▼                 ▼                  ▼
    CONGENITAL          ACQUIRED           NEOPLASTIC
         │                 │                  │
  ┌──────┴───────┐    ┌────┴────┐         ┌──┴────────┐
  │              │    │        │         │           │
Thyroglossal  Branchial  Lymphatic  Cystic    Epidermoid
Duct Cyst     Cleft Cyst  Malform.  Hygroma   Cyst

Also: Ranula, Dermoid cyst, Thymic cyst, Parathyroid cyst,
      Laryngocoele, Cystic metastasis (HPV-related HNSCC)

---

1. THYROGLOSSAL DUCT CYST (TGDC)

• Midline or just paramedian (up to 3 cm from midline)
• Infrahyoid > juxtahyoid > suprahyoid (60:25:15)
• Moves upward on tongue protrusion or swallowing (attached to hyoid bone)

• Ultrasound: Midline, thin-walled, anechoic cyst; may be echogenic if infected/proteinaceous. "Pseudosolid" appearance. Moves with swallowing.
• CT: Well-defined midline hypodense lesion, intimately related to hyoid bone. Density varies 0-25 HU (thin fluid) to higher (infected).
• MRI:
  • T1: Low signal (fluid) or high signal (proteinaceous/infected)
  • T2: Uniformly bright
  • No enhancement (unless infected)
• Key: Rule out ectopic thyroid (always perform thyroid scan/USS to confirm normal thyroid gland exists before surgery)

---

2. BRANCHIAL CLEFT CYST

• 1st branchial cleft cyst: Periauricular/parotid region
• 2nd branchial cleft cyst (most common - 90%): Anterolateral neck, lateral to carotid space, posteromedial to SCM, anterior to external carotid
• 3rd/4th branchial cleft cyst: Posterior triangle / piriform sinus

DIAGRAM: 2nd BCC Location

  External carotid ← - - [CYST] - - → SCM (anterior/deep)
  artery (medial)                       (posterior)
  Jugular vein (medial)

• Ultrasound: Anechoic (thin fluid), thin-walled, no internal echoes; posterior enhancement; may be echogenic if infected
• CT: Well-defined, thin-walled hypodense lesion (near-water density); displaces SCM posterolaterally, displaces carotid sheath medially. Posterior triangle of neck. Wall thickening + enhancement = infection.
• MRI:
  • T1: Low (watery) to intermediate (proteinaceous)
  • T2: High signal
  • DWI: No restriction (unless epidermoid)
  • Post-contrast: Thin peripheral enhancement
• Sinus/fistula tract is pathognomonic when present

---

3. CYSTIC HYGROMA / LYMPHATIC MALFORMATION

• Macrocystic (most common, > 2 cm) or microcystic type
• Posterior cervical triangle / submandibular region; may extend to mediastinum
• Large multiloculated cystic lesion

• Ultrasound: Multiloculated, anechoic/hypoechoic cysts with thin septations; no flow in cysts (flow in septa). Compressible, insinuates around structures.
• CT/MRI: Multiloculated cystic mass, crosses spaces, follows fascial planes; no enhancement of cysts (septa may enhance)
• T2 MRI: Bright multiloculated cysts with thin septations
• Fluid-fluid levels if haemorrhage has occurred (T1 bright in lower layer)

---

4. RANULA

• Retention cyst of sublingual gland
• Simple ranula: Floor of mouth, above mylohyoid
• Plunging (diving) ranula: Herniates through mylohyoid → submandibular/submental space

• MRI: T2 bright, homogeneous cyst; "tail sign" seen at mylohyoid for plunging type
• USS: Anechoic thin-walled cyst in floor of mouth/submandibular space

---

5. DERMOID / EPIDERMOID CYSTS

• Dermoid: Contains skin adnexa (hair, sebaceous), midline, floor of mouth
• CT: Fat-containing lesion (negative Hounsfield units), "sac of marbles" appearance
• MRI: T1 bright fat, T2 intermediate; DWI - restricted diffusion (key for epidermoid)
• Epidermoid: DWI restriction is pathognomonic (distinguishes from arachnoid cyst)

---

6. CYSTIC METASTATIC LYMPHADENOPATHY

• HPV-positive oropharyngeal squamous cell carcinoma
• Thyroid papillary carcinoma (thin-walled, partially cystic node)
• May be the presenting feature

---

APPROACH TO NECK CYSTIC LESION BY LOCATION

┌──────────────────┬──────────────────────────────────────────────────┐
│  Location        │  Likely Diagnosis                                │
├──────────────────┼──────────────────────────────────────────────────┤
│  Midline         │  Thyroglossal duct cyst (child/young adult)      │
│                  │  Dermoid cyst, thyroid cyst, lymphadenopathy     │
├──────────────────┼──────────────────────────────────────────────────┤
│  Anterior        │  2nd Branchial cleft cyst                        │
│  triangle,       │  Cystic metastasis (adult > 40)                  │
│  lateral         │  Lymph node                                      │
├──────────────────┼──────────────────────────────────────────────────┤
│  Posterior       │  Lymphatic malformation                           │
│  triangle        │  3rd/4th branchial cleft cyst                    │
├──────────────────┼──────────────────────────────────────────────────┤
│  Floor of        │  Ranula, dermoid, epidermoid                     │
│  mouth           │                                                  │
├──────────────────┼──────────────────────────────────────────────────┤
│  Parotid/        │  1st BCC, parotid cyst, lymph node               │
│  periauricular   │                                                  │
└──────────────────┴──────────────────────────────────────────────────┘

---

---

QUESTION 4 (2 x 10 Marks)

Q4 Part 1: SUBCLAVIAN STEAL SYNDROME

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DEFINITION

• "Steal" = the proximal subclavian occlusion causes the arm's blood supply to be "stolen" from the vertebrobasilar circulation via reversed vertebral artery flow
• Subclavian steal phenomenon = reversed VA flow without symptoms
• Subclavian steal syndrome = reversed VA flow WITH vertebrobasilar symptoms

---

PATHOPHYSIOLOGY

DIAGRAM: Subclavian Steal Syndrome Mechanism

Normal:                        Subclavian Steal:
Aorta                          Aorta
  │                              │
  ├──→ Subclavian A.             ├──X──→ Subclavian A. [OCCLUDED]
  │        │                     │
  │        └──→ Vertebral A. ↓   │
  │                              ├──→ Vertebral A. (other side)
  └──→ Vertebral A. ↑            │         │
            │                    │         ↓ Basilar A.
            ↓                    │              │
         Basilar A.              │         Blood REVERSES back
                                 │         into ipsilateral VA
                                 │         to supply arm
  On Arm Exercise:
  ↑ Demand in arm muscles
  ↓ Peripheral resistance in arm
  ← Flow reverses up contralateral VA
     → Basilar → ipsilateral VA (retrograde)
     → Subclavian distal to stenosis

• Atherosclerosis (most common - left subclavian > right)
• Takayasu's arteritis (especially in young Asian women)
• Radiation-induced stenosis
• Congenital anomaly
• Thoracic outlet syndrome

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CLINICAL FEATURES

• Arm: Exercise-induced claudication, arm fatigue, coldness; ipsilateral arm BP lower by > 20 mmHg
• Vertebrobasilar symptoms (on arm exercise): Dizziness, vertigo, ataxia, diplopia, drop attacks, visual disturbances
• Bruit over the subclavian/supraclavicular region
• Coronary subclavian steal: In post-CABG patients with LIMA graft - arm exercise can steal flow from LIMA graft causing angina

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RADIOLOGY

1. DOPPLER ULTRASOUND (First-line)

• Colour Doppler: Retrograde/reversed flow in ipsilateral vertebral artery
• Spectral Doppler: Vertebral artery flow shows:
  • Complete reversal (continuous antegrade → complete retrograde)
  • Partial reversal ("to-and-fro" or "bunny rabbit" pattern = alternating flow)
  • Biphasic waveform (transitional steal)
• Provocative test: Arm exercise or blood pressure cuff inflation on affected arm amplifies reversed flow
• Subclavian artery: Monophasic/dampened waveform distal to stenosis; stenotic jet at origin

2. CT ANGIOGRAPHY (CTA)

• Modality of choice for vascular anatomy and surgical planning
• Shows stenosis or occlusion of proximal subclavian artery (origin)
• 3D reconstruction: Depicts collateral pathways
• Left subclavian occlusion arrow on axial CT (as seen in textbook image below)

3. MR ANGIOGRAPHY (MRA)

• Time-of-Flight (TOF) MRA:
  • "Localizer sign" (2D TOF): Normal antegrade VA flow appears bright; reversed flow appears dark on saturation pulse technique
  • Phase-contrast MRA: Directly encodes flow direction
• CE-MRA (Contrast-enhanced):
  • Demonstrates occlusion of subclavian artery
  • Time-resolved CEMRA: Shows the dynamic reversal of vertebral artery flow in real time
  • Shows filling of distal subclavian via retrograde vertebral route
• Avoids radiation (preferred in young patients)

4. DIGITAL SUBTRACTION ANGIOGRAPHY (DSA)

• Historically gold standard; now reserved for pre-intervention planning
• Demonstrates:
  • Subclavian stenosis/occlusion
  • Retrograde flow in vertebral artery (shown on sequential images)
  • Contralateral vertebral artery as the donor vessel

5. CONVENTIONAL ANGIOGRAPHY

• Retrograde filling of ipsilateral vertebral artery through basilar artery

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MRA SPECIFIC SIGNS

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TREATMENT

• Angioplasty + stenting of proximal subclavian stenosis (endovascular - first choice)
• Surgical bypass: Carotid-subclavian bypass or subclavian transposition (for long occlusions)

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DDx of Vertebrobasilar TIA

• Vestibular disease (no arm BP difference, no reversed VA flow)
• Vertebral artery dissection (MRI: T1 bright mural hematoma)
• Cardiac embolism
• Vertebrobasilar atherosclerosis (not related to arm exercise)

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Q4 Part 2: PSEUDOTUMOUR OF THE ORBIT (Idiopathic Orbital Inflammatory Disease - IOID)

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DEFINITION

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EPIDEMIOLOGY

• Most common painful orbital mass in adults
• Any age; bilateral in 10-15% (more common in children)
• Equal sex distribution

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PATHOLOGY AND CLASSIFICATION

┌──────────────────────────────────────────────────────────────────┐
│  CLASSIFICATION BY ANATOMICAL SUBTYPE                            │
│                                                                  │
│  1. Myositis (most common) - extraocular muscle                  │
│  2. Dacryoadenitis - lacrimal gland                             │
│  3. Scleritis/Perineuritis - sclera/optic nerve sheath          │
│  4. Anterior pseudotumour - anterior orbit                       │
│  5. Diffuse pseudotumour - entire orbit                          │
│  6. Apical pseudotumour - orbital apex (Tolosa-Hunt if extends   │
│     to cavernous sinus = same spectrum)                          │
└──────────────────────────────────────────────────────────────────┘

• Fibrosclerotic (densest fibrosis, less steroid responsive)
• Lymphocytic (most common)
• Mixed
• Granulomatous

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CLINICAL FEATURES

• Sudden onset painful proptosis (proptosis + pain = characteristic)
• Diplopia (muscle involvement)
• Lid swelling, chemosis, injection
• Restricted ocular movement
• Reduced vision (apical involvement → optic nerve compression)
• Bilateral in 10% (think systemic lymphoma/IgG4-related disease if bilateral)
• Dramatic response to oral steroids is both diagnostic and therapeutic

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RADIOLOGY

1. ULTRASOUND (B-scan)

• Orbital myositis: Thickened, hypoechoic extraocular muscle; INCLUDES the tendon (differs from thyroid eye disease)
• Lacrimal gland: Enlarged, lobulated
• Diffuse: Irregular hypoechoic mass with moderate internal reflectivity
• Posterior acoustic shadowing absent
• Fluid in Tenon's capsule (Tenon's cyst sign in sclerosing type)

2. CT SCAN

• Orbital myositis:
  • Diffuse thickening of extraocular muscle including tendon (key differentiator from TED)
  • Medial rectus and superior rectus most affected
  • Enhances homogeneously
• Diffuse IOID:
  • Irregular, infiltrative soft tissue mass moulding around the globe ("dirty fat" - haziness of orbital fat)
  • Poor planes of cleavage with optic nerve/muscle
  • No bony destruction (important negative finding)
• Lacrimal gland type: Enlarged, enhancing lacrimal gland in anterosuperolateral orbit
• Sclerosing type: Diffuse enhancing thickening around the sclera and Tenon's capsule

DIAGRAM: CT Orbit - Orbital Myositis in IOID

                  [Optic nerve]
         [Superior  |
         Oblique]   |    [Superior Rectus THICKENED]
    ─────────────[Globe]──────────────
         [Inferior  |    [Inferior Rectus]
         Rectus]    |
              [Medial Rectus THICKENED +
               tendon involved]
Note: Tendon involvement distinguishes IOID from TED

3. MRI (Investigation of choice)

• T1: Isointense to muscle (intermediate signal)
• T2: Classically hypointense (fibrous/sclerosing subtypes) - KEY FEATURE
  • More cellular forms may be T2 hyperintense
• T1+Gad: Moderate to marked enhancement
• Myositis type: Thickened muscle belly + tendon
• Diffuse type: Infiltrative enhancing mass surrounding the globe; fills orbital fat planes
• Apical type: Infiltrative tissue in orbital apex, may extend to cavernous sinus
• Bilateral disease: Suspect lymphoma, IgG4-RD, sarcoidosis, Wegener's

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KEY IMAGING DIFFERENTIALS

┌─────────────────────┬──────────────────────────────────────────────────────────┐
│  Condition          │  Key Distinguishing Features                             │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Thyroid Eye        │  Bilateral (90%), muscle belly SPARES tendon,            │
│  Disease (TED)      │  inferior/medial rectus > others, no pain                │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Orbital Lymphoma   │  B-cell lymphoma; bilateral; homogeneous; T1/T2 iso;     │
│                     │  molds to globe ("salmon patch"); no bony destruction;   │
│                     │  FDG-PET avid; biopsy required                           │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Orbital Cellulitis │  Pre/post-septal; sinusitis as origin; fever; USG shows  │
│                     │  subperiosteal abscess; no myositis pattern              │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  IgG4-Related       │  Bilateral dacryoadenitis, bilateral orbital disease;    │
│  Orbital Disease    │  elevated serum IgG4; multi-organ involvement            │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Cavernous          │  Circumscribed; progressive proptosis (painless);        │
│  Haemangioma        │  T2 very bright; progressive fill-in on dynamic MRI;     │
│                     │  intraconal; most common benign orbital tumour           │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Orbital Metastasis │  History of primary; bone destruction; irregular margins │
│                     │  breast (scirrhous → enophthalmos), lung, GI             │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Sarcoidosis        │  Lacrimal gland; bilateral; hilar lymphadenopathy        │
│  Orbital            │  on chest X-ray; elevated ACE; non-caseating granuloma  │
├─────────────────────┼──────────────────────────────────────────────────────────┤
│  Orbital            │  Proptosis + ophthalmoplegia + chemosis (Tolosa-Hunt);   │
│  Pseudotumour at    │  extends to cavernous sinus; very painful;               │
│  apex (Tolosa-Hunt) │  dramatic steroid response                               │
└─────────────────────┴──────────────────────────────────────────────────────────┘

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ORBITAL PSEUDOTUMOUR vs THYROID EYE DISEASE - KEY DIFFERENTIATOR TABLE

┌─────────────────┬───────────────────────────┬─────────────────────────────┐
│  Feature        │  Orbital Pseudotumour      │  Thyroid Eye Disease        │
├─────────────────┼───────────────────────────┼─────────────────────────────┤
│  Pain           │  YES (hallmark)            │  Mild/absent               │
│  Laterality     │  Unilateral (mostly)       │  Bilateral (90%)           │
│  Tendon         │  Included (thickened)      │  Spared (belly only)       │
│  Muscles        │  Any, incl tendon          │  Inferior > medial >       │
│                 │                            │  superior > lateral (IMSLO)│
│  Thyroid tests  │  Normal                    │  Abnormal                  │
│  Steroid resp.  │  Dramatic                  │  Moderate                  │
│  Bony changes   │  Absent                    │  Absent                    │
└─────────────────┴───────────────────────────┴─────────────────────────────┘

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MANAGEMENT

• Oral corticosteroids (1 mg/kg/day prednisolone) - dramatic response within 48-72 hours is both diagnostic and therapeutic
• Recurrence after steroid taper → consider biopsy to rule out lymphoma, IgG4
• Sclerosing subtype: Poor steroid response; may need radiotherapy or immunosuppressants
• Biopsy indicated when: atypical presentation, steroid failure, recurrence, bilateral disease

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