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RADIOLOGY UNIVERSITY EXAM - COMPLETE ANSWERS (50 Marks)

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Q1. Newer Imaging Techniques in PNS Pathologies Including Immune-Suppressed Patients

Conventional Approach (Baseline)

CT Advances

• Ultra-low-dose CT (ULDCT): Preserves diagnostic quality at reduced radiation dose - important for repeated imaging in chronic rhinosinusitis
• Cone-Beam CT (CBCT): Lower dose than conventional CT, used for pre-surgical planning and chronic sinonasal disease
• Multiplanar reconstruction (MPR): Coronal and sagittal reformats are mandatory for sinus surgery planning; better than axial alone
• Bone algorithm + soft tissue window: Used together - bone for bony erosion, soft tissue for mucosal and extra-sinus disease

MRI Advances

• T2-weighted sequences: Best for differentiating retained secretions (bright T2) from fungal disease (dark T2 due to metal concentration in mucin) and tumour
• Diffusion-Weighted Imaging (DWI): Increasingly important - abscesses show restricted diffusion (low ADC); helps distinguish tumour from retained secretions; useful in cholesterol granuloma
• Dynamic Contrast-Enhanced MRI (DCE-MRI): Used to assess tumour vascularity and perineural spread
• STIR sequences: Excellent for inflammatory oedema in orbit and skull base
• SWI (Susceptibility-Weighted Imaging): Detects haemorrhage and iron deposition
• MR Angiography (3D TOF): Assesses carotid artery involvement in aggressive invasive disease

PET-CT

• 18F-FDG PET-CT: Used for staging sinonasal malignancies, detecting regional nodal metastases, and surveillance post-treatment

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In Immune-Suppressed Patients (Special Protocol)

• Non-contrast CT: Hypoattenuating mucosal thickening in sinuses (early), bony erosion and perforation (later)
• Obliteration of periantral fat planes (very early and subtle - often the first CT sign)
• CT demonstrates bony destruction (skull base, orbital walls, pterygopalatine fossa)

• T2 hypointense thickened mucosa - the earliest and most frequent MRI finding (seen in ~94% of AIFRS cases)
• Necrosis - second most frequent finding
• MRI is superior for orbital involvement: inflammatory changes in orbital fat, extraocular muscle thickening, proptosis
• Leptomeningeal enhancement = early intracranial extension (pre-infarction stage)
• Cavernous sinus involvement = thrombosis, seen as expansion and filling defect on post-contrast T1
• Cerebral infarction: DWI shows restricted diffusion - represents angioinvasion-mediated thrombosis
• Periantral fat stranding and obliteration on fat-suppressed sequences indicates early extra-sinus spread

1. DWI whole brain (b-1000)
2. FLAIR whole brain
3. SWI (for haemorrhage detection)
4. T2 TSE - small FOV for PNS and orbits (coronal + axial, 3.5 mm slices)
5. STIR long TE for PNS and orbits
6. T1 TSE small FOV
7. Oblique sagittal T1 for orbits
8. Post-contrast 3D T1 fat-suppressed (DCE)
9. MR Angiography 3D TOF (carotid assessment)

Rule: In immunocompromised patients, 9/10 cases of sinus disease with orbital signs = fungal infection; 1/10 = lymphoma. A high index of suspicion is mandatory even with normal nasoendoscopy.

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Q2. Causes of Unilateral Proptosis + Imaging Features of Optic Nerve Glioma

Causes of Unilateral Proptosis (in decreasing order of frequency)

• Cavernous sinus fistula (pulsatile proptosis)
• Thyroid Eye Disease / Graves' ophthalmopathy (though classically bilateral, can be unilateral)
• Lacrimal gland tumour (adenoid cystic carcinoma, pleomorphic adenoma)
• Orbital meningioma
• Schwannoma
• Lymphoma (MALT)
• Langerhans Cell Histiocytosis

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Imaging Features of Optic Nerve Glioma

• Fusiform (spindle-shaped) enlargement of the optic nerve
• Iso- to hyperdense compared to normal nerve
• May show expansion and erosion of the optic canal
• Does NOT show calcification (unlike meningioma - important distinguishing point)
• Enhancement with contrast is variable

• Shape: Fusiform (tubular/kinking/buckling) enlargement of the optic nerve
• T1: Isointense to hypointense compared to white matter
• T2: Hyperintense
• Post-Gadolinium (T1+C): Variable contrast enhancement - may be homogeneous or heterogeneous
• Extension: May extend posteriorly through the optic canal into the optic chiasm, optic tracts, and hypothalamus (optic pathway glioma)
• NF1 association: Look for other stigmata - plexiform neurofibroma, sphenoid wing dysplasia
• No calcification (this distinguishes from optic nerve sheath meningioma)

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Q3. Carcinoma of Maxilla - Imaging

Classification Aid: Ohgren's Line

• A line drawn from the medial canthus of the eye to the angle of the mandible divides the maxilla
• Suprastructure (above Ohgren's line): Involves orbit, ethmoid, sphenoid - worse prognosis
• Infrastructure (below Ohgren's line): Involves palate, alveolus - better prognosis

Modalities Used

• Water's view: Opacification of maxillary sinus, bony erosion of antral walls
• Lateral view and OPG: Dental involvement

• Preferred: CECT with bone algorithm + soft tissue window
• Features of malignancy:
  • Ill-defined, heterogeneously enhancing bulky mass in maxillary sinus
  • Extensive bony destruction (irregular, aggressive pattern)
  • Loss of normal sinus walls
  • Nodal metastases in levels Ia, Ib, II, III
• CT assesses: Orbital floor, ethmoid sinus, pterygoid plates, pterygopalatine fossa, infratemporal fossa, palate, nasal cavity
• Bone algorithm reconstruction (MDCT): Mandatory for bony detail

• Superior for: Soft tissue invasion, perineural spread, orbital content involvement, intracranial extension, dural involvement, bone marrow invasion
• SCC of maxilla: T1 isointense, T2 intermediate-to-high signal with post-contrast enhancement
• Perineural spread: Enhancing, enlarged trigeminal nerve branches (V2 via infraorbital canal) - seen on fat-suppressed T1 post-contrast
• MRI better distinguishes tumour from retained secretions (tumour restricts diffusion on DWI; secretions do not)
• Invasion of orbital periosteum, fat, and extraocular muscles is best seen on MRI

• Detects regional and distant metastases
• Used in staging and post-treatment surveillance
• Identifies occult nodal disease and second primaries

• T1: Tumour limited to antral mucosa (no bone erosion)
• T2: Erosion of infrastructure, including hard palate
• T3: Invasion of orbital floor, ethmoid sinuses, posterior wall, pterygoid plates
• T4a: Orbital contents, cribriform plate, pterygoid fossa, nasopharynx, sphenoid - resectable
• T4b: Orbital apex, dura, brain, middle cranial fossa, cranial nerves other than V2 - unresectable

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Q4. Endocrinal (Dental) Manifestation - Thyroid Lesion: Investigation at a Fully Equipped Radiology Centre

Step-by-Step Investigation Protocol

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• Composition: Solid / mixed / purely cystic (purely cystic = benign)
• Echogenicity: Marked hypoechogenicity = suspicious
• Margins: Irregular / microlobulated = suspicious; smooth = benign
• Orientation: Taller-than-wide (anti-parallel) = suspicious
• Calcifications: Microcalcifications (punctate echogenic foci) = highest suspicion for papillary carcinoma; coarse/eggshell = benign
• Vascularity: Increased central vascularity = suspicious

• TR1 (0 points) = Benign; TR5 (≥7 points) = High suspicion malignancy

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• Indicated for: Solid hypoechoic nodule >1 cm; any nodule with suspicious features; PET-avid nodule
• Bethesda reporting system: I (non-diagnostic) to VI (malignant)
• Sensitivity ~95%, specificity ~99% for papillary carcinoma

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• Tc-99m pertechnetate (most common): Assesses function
  • Hot nodule (functioning): Suppresses surrounding tissue; rarely malignant (<1%)
  • Cold nodule (non-functioning): 5-15% malignancy risk - requires FNAC
  • Warm/indeterminate: Background uptake; requires further workup
• I-123/I-131 scintigraphy: Indicated for hyperthyroidism workup; used in detecting toxic adenoma, multinodular goitre, Graves' disease (diffuse uptake)

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• CECT neck + chest: Staging for known/suspected thyroid malignancy
• Assess: Tracheal displacement/compression, retrosternal extension of goitre, local invasion (trachea, oesophagus, carotid artery), nodal metastases
• Avoid iodinated contrast before I-131 therapy (contrast blocks iodine uptake for 6-8 weeks)
• On CT: Thyroid normally very hyperdense (100-150 HU) due to iodine content; malignant lesions appear as ill-defined hypodense areas with extrathyroidal extension

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• Better for: Retrosternal goitre, tracheal compression, perineural spread, recurrent disease, allergy to CT contrast
• T1: Thyroid isointense to muscle; colloid/haemorrhagic cysts show T1 bright foci
• T2: Benign adenoma bright; malignancy often heterogeneous

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• FDG-avid incidental thyroid nodule: Risk of malignancy ~35% - mandatory FNAC
• Used for staging and restaging of differentiated thyroid carcinoma
• I-131 whole body scan: Post-thyroidectomy, to detect residual/metastatic differentiated thyroid carcinoma (follicular, papillary)

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Thyroid lesion detected
         ↓
   USG + TIRADS scoring
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   TSH + Scintigraphy (if TSH low → hot nodule → no FNAC)
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   Cold/Warm nodule OR suspicious USG features
         ↓
   USG-guided FNAC (Bethesda classification)
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   If malignant/indeterminate → CECT neck + chest for staging
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   PET-CT for metastatic workup / post-op surveillance

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Q5. Radiological Anatomy of the Oral Cavity (Draw and Label)

Subsites of the Oral Cavity (for diagram)

• Anteriorly: Vermilion border of lips
• Posteriorly: Circumvallate papillae of tongue + anterior tonsillar pillars (hard/soft palate junction on imaging)
• Roof: Hard palate
• Floor: Mylohyoid muscle (forms the floor of mouth sling)
• Lateral walls: Buccinator muscles

1. Lips (upper and lower)
2. Buccal mucosa
3. Upper alveolar ridge + gingiva
4. Lower alveolar ridge + gingiva
5. Oral tongue (anterior 2/3)
6. Floor of mouth (FOM)
7. Hard palate
8. Retromolar trigone

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Axial CT/MRI Anatomy - Key Levels

• Mandible (M) - U-shaped bony boundary
• Mylohyoid muscle (MH) - floor of mouth sling dividing sublingual space (above) from submandibular space (below)
• Genioglossus muscle (GG) - largest extrinsic tongue muscle, paramedian
• Geniohyoid muscle (GH) - below genioglossus
• Hyoglossus muscle (HG) - lateral surface of tongue
• Sublingual gland (SLG) - above mylohyoid
• Deep portion of submandibular gland - below mylohyoid
• Lingual septum - midline fibrous structure dividing tongue
• Intrinsic tongue muscles (longitudinal, transverse, vertical)
• Lingual artery - between hyoglossus and genioglossus

• Sublingual space: Above mylohyoid, contains sublingual gland, lingual nerve, Wharton's duct, deep submandibular gland
• Submandibular space: Below mylohyoid, contains superficial submandibular gland, lymph nodes
• Buccal space: Contains buccal fat pad (important landmark)

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Diagram Label Guide:

CORONAL T2 MRI - ORAL CAVITY

        Hard Palate (HP)
              |
    [Oral Cavity / Tongue]
    Intrinsic muscles (TIM)
              |
    Lingual Septum (LS)
   /                    \
Sublingual gland (SLG)  Sublingual gland (SLG)
Genioglossus (GG)       Genioglossus (GG)
Geniohyoid (GH)         Geniohyoid (GH)
              |
    Mylohyoid sling (MH) ← floor of mouth
   /                    \
Submandibular space     Submandibular space
(SMG, lymph nodes)      (SMG, lymph nodes)
              |
    Mandibular body (MB)

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Q6. Short Note 1: Branchial Cleft Cyst

Embryology

Classification

• Type I: Ectoderm only; superficial to parotid/facial nerve; duplication of EAC
• Type II: Ectoderm + mesoderm (cartilage); may be within/deep to parotid, variable facial nerve relationship

Imaging Features (2nd BCC - Most Classic)

• Well-defined, thin-walled, anechoic or hypoechoic oval cystic mass
• May show internal echoes if infected or contains proteinaceous fluid
• No internal vascularity (unless infected)

• Well-defined, smoothly marginated oval or round cystic mass
• Located anterior to SCM, lateral to carotid vessels, posterior to submandibular gland
• Attenuation: Water density (0-20 HU) - fluid contents
• Thin imperceptible wall (if uncomplicated); thickened enhancing wall if infected
• Displaces but does not invade adjacent structures
• A sinus/fistula tract may be visible extending to skin anteriorly

• T1: Low signal (if simple fluid) or intermediate/high signal (if proteinaceous/haemorrhagic)
• T2: Uniformly high signal (bright)
• Post-contrast: No internal enhancement (wall only if infected)
• Best defines relationship to carotid sheath, facial nerve

Differential Diagnosis

• Lymph node cystic metastasis (SCC, papillary thyroid carcinoma)
• Thyroglossal duct cyst (midline, moves with swallowing)
• Cystic hygroma (lymphangioma)
• Epidermoid/dermoid cyst
• Ranula (plunging type)

Management

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Q7. Short Note 2: PNS Mucormycosis

Definition and Organism

At-Risk Patients

• Diabetics with DKA (most at risk - Mucorales have ketone reductase systems and thrive in high glucose, acidotic environments)
• Haematologic malignancy / severe neutropenia
• Stem cell / bone marrow transplant recipients
• Systemic chemotherapy
• Prolonged high-dose steroid use
• Iron overload + deferoxamine therapy (Rhizopus binds deferoxamine)
• AIDS
• Post-COVID mucormycosis (a major epidemic pattern seen in 2021-22 among diabetic COVID-19 patients)

Pathophysiology

Clinical Features

• Classic triad: Fever + nasal congestion + facial pain in an immunocompromised patient
• Pale/necrotic nasal mucosa (insensate due to ischaemia)
• Black eschar on palate or nasal septum = pathognomonic
• Orbital involvement: Proptosis, orbital apex syndrome, ophthalmoplegia, vision loss
• Intracranial: Altered sensorium, hemiplegia, seizures

Imaging Features

• Non-contrast CT: Hypoattenuating mucosal thickening (unilateral sinus disease is typical early)
• Bony erosion and destruction of sinus walls - a hallmark of invasive disease
• Obliteration of periantral fat planes (very early CT sign - subtle)
• Destruction of medial orbital wall, orbital floor
• Involvement of pterygopalatine fossa and infratemporal fossa
• Bone algorithm: Best for detecting fine bony erosion

• T2 hypointense mucosa in affected sinuses - earliest and most frequent MRI finding (seen in ~94% of AIFRS)
  • Due to iron-containing fungal elements and desiccated necrotic tissue
  • This is the opposite of typical sinusitis which shows T2 bright mucosa
• Necrosis - second most common finding (~93%)
• Periantral fat stranding: Loss of normal bright fat signal on T1 on fat-sat sequences
• Orbital involvement: Inflammatory stranding of orbital fat, extraocular muscle thickening, proptosis
• Cavernous sinus thrombosis: Filling defect on post-contrast T1; expansion of cavernous sinus
• Carotid artery: Narrowing, pseudo-aneurysm, infarction on DWI
• Intracranial extension: Leptomeningeal enhancement → cerebral oedema → DWI-restricted infarction
• No enhancement in necrotic tissue - distinguishes from enhancing tumour

• Assess carotid artery involvement - thrombosis or pseudo-aneurysm
• Intracranial vascular involvement can be fatal

Spread Pattern (Rhinocerebral Mucormycosis)

Diagnosis

• Nasoendoscopy + biopsy: Pale/black mucosa. KOH preparation shows broad, non-septate (ribbon-like) hyphae with right-angle branching (vs. Aspergillus: narrow, septate, 45° branching)
• Frozen section: Sensitivity 84%, specificity 100% for invasive disease
• Culture: Only 54% sensitive

Treatment

1. Reverse immunosuppression (control DKA, reduce steroids)
2. Aggressive surgical debridement (endoscopic preferred over open)
3. Amphotericin B deoxycholate (1-1.5 mg/kg/day) - first-line antifungal
   • Liposomal Amphotericin B (5-10 mg/kg/day) - less nephrotoxic, preferred in cancer patients
4. Posaconazole as step-down oral therapy
5. Hyperbaric oxygen - adjunctive (inhibits fungal growth)

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Key Differentiating Radiology Table - Fungal Sinusitis

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