RS

Gross Identification (Tier 1) Identify the disease from a lung specimen showing uniform, diffuse consolidation involving an entire lobe with a firm, liver-like consistency, and list the 4 characteristic gross stages.

Diagnosis: Lobar Pneumonia

Gross Stages:

1. Stage of Congestion: Heavy, boggy, dark red lung
2. Stage of Red Hepatization: Firm, airless, dry, red-brown liver-like consistency
3. Stage of Grey Hepatization: Dry, grey-brown, firm surface with fibrinopurulent pleurisy
4. Stage of Resolution: Soft, granular, yellow-grey exudate undergoing enzymatic digestion

Microscopy Identification (Tier 1) Identify the condition and differentiate between the high-power microscopic alveolar contents of Red Hepatization vs Grey Hepatization.

Diagnosis: Lobar Pneumonia

LOW POWER:

• Uniform filling of all contiguous alveolar spaces across a lobe with preserved alveolar wall architecture.

HIGH POWER:

• Red Hepatization: Alveolar capillaries intensely congested; alveoli packed with neutrophils, intact red blood cells, and fibrin strands.
• Grey Hepatization: Capillaries compressed/ischemic; alveoli filled with dense fibrin networks and disintegrating neutrophils; red blood cells lysed.

Histology Hallmark (Tier 1) What is the characteristic microscopic hallmark of Lobar Pneumonia in the stage of red hepatization?

Massive, uniform intra-alveolar consolidation composed of densely packed neutrophils, fibrin networks, and extravasated red blood cells with intact alveolar septa.

Gross Identification (Tier 1) Identify the pediatric entity showing a subpleural parenchymal lesion in the lower upper lobe along with enlarged, caseous hilar lymph nodes. List its 3 constituent components.

Diagnosis: Ghon Complex (Primary Pulmonary Tuberculosis)

Components:

1. Ghon Focus: $1-1.5\,\text{cm}$ subpleural grey-white caseous parenchymal lesion (typically lower part of upper lobe or upper part of lower lobe)
2. Tuberculous Lymphangitis: Inflamed lymphatic channels draining the lesion
3. Tuberculous Lymphadenitis: Enlarged, matted, caseous tracheobronchial/hilar lymph nodes

Microscopy Identification (Tier 1) Identify the disease from a lung biopsy showing central acellular eosinophilic granular debris surrounded by epithelioid histiocytes, Langhans giant cells, and a peripheral lymphocytic mantle.

Diagnosis: Pulmonary Tuberculosis (Caseating Granulomatous Inflammation)

Microscopic Features:

• Central structureless, eosinophilic, granular caseous necrosis
• Surrounding rim of epithelioid cells (transformed histiocytes with slipper-shaped nuclei)
• Langhans giant cells with horseshoe-shaped peripheral nuclei
• Outer collar of lymphocytes and fibroblasts
• Ziehl-Neelsen (ZN) stain demonstrates acid-fast bacilli (AFB)

Histology Hallmark (Tier 1) What is the characteristic microscopic hallmark of Pulmonary Tuberculosis?

Caseating granuloma (tubercle) characterized by central structureless caseous necrosis surrounded by epithelioid histiocytes, multinucleating Langhans giant cells, and lymphocytes.

Microscopy Identification (Tier 1) Identify this central hilar lung mass showing nests of polygonal malignant cells with abundant eosinophilic cytoplasm, intercellular bridges, and concentric eosinophilic pearls.

Diagnosis: Squamous Cell Carcinoma of the Lung

Microscopic Features:

• Architecture: Infiltrating sheets, cords, and nests of malignant epithelial cells with desmoplastic stroma
• Cell Morphology: Large, polygonal cells with abundant eosinophilic cytoplasm
• Nuclear Features: Hyperchromatic, pleomorphic nuclei with coarse chromatin
• Diagnostic Structures: Intercellular bridges (desmosomes) and keratin pearls (concentric lamellae of eosinophilic keratin)

Microscopy Identification (Tier 1) Identify the central pulmonary tumor showing dark, small round-to-oval cells with scant cytoplasm, granular "salt-and-pepper" chromatin, extensive necrosis, and nuclear molding.

Diagnosis: Small Cell Carcinoma (Oat Cell Carcinoma) of the Lung

Microscopic Features:

• Architecture: Diffuse sheets, clusters, or ribbons of uniform small malignant cells
• Cell Morphology: Scant cytoplasm, poorly defined cell borders (size $2-3\times$ lymphocyte)
• Nuclear Features: Finely granular "salt-and-pepper" chromatin, absent or inconspicuous nucleoli, and nuclear molding
• Stromal Features: Extensive ischemic necrosis and Azzopardi effect (basophilic DNA deposition on blood vessel walls)

Microscopy Identification (Tier 1) Identify the peripheral lung mass showing malignant cuboidal-to-columnar epithelial cells arranged in glandular or acinar patterns with intracellular and extracellular mucin production.

Diagnosis: Adenocarcinoma of the Lung

Microscopic Features:

• Architecture: Infiltrative acinar, papillary, micropapillary, or solid patterns
• Cell Morphology: Columnar or cuboidal cells lining neoplastic glands
• Nuclear Features: Pleomorphic, hyperchromatic nuclei with prominent nucleoli
• Special Stains: Positive mucin staining with Mucicarmine or Periodic Acid-Schiff (PAS) with diastase

Gross Identification (Tier 1) Identify this lung specimen showing markedly dilated bronchi extending almost to the visceral pleura, filled with mucopurulent exudate, giving a honeycomb/cut-can appearance.

Diagnosis: Bronchiectasis

Gross Features:

• Dilated bronchi and bronchioles (saccular, cylindrical, or fusiform)
• Dilatations extend to the subpleural surface (normally bronchi are absent within $1\,\text{cm}$ of pleura)
• Bronchial lumina packed with thick, foul-smelling mucopurulent secretion
• Bronchial walls thickened and fibrosed with surrounding atelectasis

Microscopy Identification (Tier 1) Identify the chronic airway pathology displaying bronchial epithelial ulceration, intense transmural acute and chronic inflammatory infiltrate, and destruction of smooth muscle and elastic fibers.

Diagnosis: Bronchiectasis

LOW POWER:

• Markedly enlarged bronchial lumina surrounded by chronically inflamed and fibrotic tissue.

HIGH POWER:

• Desquamation/ulceration of pseudostratified ciliated columnar epithelium (or squamous metaplasia)
• Dense transmural inflammatory infiltrate (neutrophils, lymphocytes, plasma cells)
• Complete destruction of normal bronchial wall components (smooth muscle, elastic tissue, and cartilage) replaced by fibrosis

Gross & Low Power Identification (Tier 1) Identify the condition characterized grossly by voluminous, pale, hyperinflated lungs covering the mediastinum, and microscopically by enlarged airspaces distal to terminal bronchioles with septal wall destruction.

Diagnosis: Emphysema

Gross Features:

• Voluminous, pale, pillowy lungs that overlap the heart
• Subpleural bullae (air-filled spaces) may be present

LOW POWER MICROSCOPY:

• Abnormally enlarged alveolar spaces distal to terminal bronchioles
• Thinning, rupture, and loss of alveolar septa creating large confluent air sacs
• Floating isolated septal stubs with diminished pulmonary capillary beds

Histology Hallmark & Image Detail (Tier 2) Identify the clinical condition and list the 3 characteristic microscopic components found in the thick mucous plugs of this obstructive airway disease.

Diagnosis: Bronchial Asthma

Microscopic Structures:

1. Curschmann Spirals: Mucus plugs containing whorled collections of shed epithelial cells
2. Charcot-Leyden Crystals: Hexagonal, diamond-shaped crystalloids composed of eosinophil galectin-10
3. Creola Bodies: Compact clusters of shed ciliated columnar cells
4. Wall Features: Subepithelial basement membrane thickening, eosinophilic infiltrate, and smooth muscle hypertrophy

Microscopy Identification & Formula (Tier 2) Identify the airway pathology showing mucous gland hyperplasia and state the formula/normal value for the Reid Index.

Diagnosis: Chronic Bronchitis

Microscopic Features:

• Submucosal mucin-secreting gland hypertrophy and hyperplasia in large airways
• Goblet cell metaplasia in peripheral bronchioles
• Chronic inflammatory infiltrate (lymphocytes, plasma cells) in lamina propria

Reid Index:

• $\text{Reid Index} = \frac{\text{Submucosal Gland Thickness}}{\text{Total Bronchial Wall Thickness (Basement Membrane to Cartilage)}}$
• Normal: $< 0.4$
• Chronic Bronchitis: $> 0.5$

Gross & Microscopic Identification (Tier 2) Identify the acute pulmonary infection characterized grossly by patchy, elevated, bilateral consolidated foci centered on bronchioles, and microscopically by focal suppurative inflammation with normal intervening alveoli.

Diagnosis: Bronchopneumonia

Gross Features:

• Patchy, dry, firm, elevated grey-red consolidated areas ($1-4\,\text{cm}$), usually bilateral and basal

Microscopic Features:

• Low Power: Patchy suppurative inflammation centered on bronchioles with intervening normal/aerated alveoli
• High Power: Bronchioles and adjacent alveolar spaces packed with neutrophilic exudate, cellular debris, and fibrin

Histology Hallmark & Microscopic Features (Tier 2) Identify the occupational lung disease showing nodular lesions composed of concentric, whorled hyalinized collagen fibers with peripheral polarization displaying birefringent needle-like particles.

Diagnosis: Silicosis

Microscopic Hallmark:

• Silicotic Nodule: Concentric, whorled, heavily hyalinized collagen fibers with an acellular center
• Peripheral mantle of dust-laden macrophages and lymphocytes

Polarizing Microscopy:

• Birefringent, needle-like crystalline silica ($SiO_2$) particles within the nodule

Image Detail (Tier 2) Identify the characteristic golden-brown, dumbbell-shaped beaded rod structure seen in pulmonary asbestos exposure and state its specific stain.

Structure: Asbestos Body (Ferruginous Body)

Significance:

• Diagnostic of Asbestosis / heavy asbestos exposure
• Composed of an inorganic asbestos fiber core coated with a protein-iron complex (hemosiderin)
• Stains bright blue with Prussian Blue (Perls') stain

Gross & Microscopic Identification (Tier 3) Identify the localized necrotizing lesion showing a central cavity filled with purulent debris surrounded by a fibrous rim and pyogenic membrane.

Diagnosis: Lung Abscess

Gross Features:

• Single or multiple localized parenchymal cavities containing suppurative necrotic material

Microscopic Features:

• Center: Suppurative liquefactive necrosis packed with degenerating neutrophils and tissue debris
• Rim: Pyogenic membrane composed of vascular granulation tissue, neutrophils, and fibroblasts
• Wall: Outer fibrous zone with surrounding atelectatic, congested pulmonary parenchyma

Histology Hallmark & Microscopy (Tier 3) Identify the malignant pleural tumor displaying a biphasic pattern of epithelioid and sarcomatoid cells that stains positive for Calretinin and WT-1.

Diagnosis: Malignant Mesothelioma

Microscopic Features:

• Biphasic Pattern: Combination of tubular/papillary epithelioid structures (cuboidal cells) and spindle/sarcomatoid stromal cells
• Diagnostic Marker: Calretinin (+), Cytokeratin 5/6 (+), WT-1 (+), and MOC-31/CEA (-)

Differentiation (Tier 1) Compare the microscopic nuclear and cytoplasmic features of Small Cell Carcinoma vs Squamous Cell Carcinoma of the lung.

Small Cell Carcinoma:

• Cytoplasm: Scant, indistinct cell boundaries
• Nuclei: Small, granular "salt-and-pepper" chromatin, inconspicuous nucleoli, prominent nuclear molding
• Necrosis: Extensive with Azzopardi effect

Squamous Cell Carcinoma:

• Cytoplasm: Abundant, eosinophilic, rigid
• Nuclei: Large, hyperchromatic, pleomorphic with prominent nucleoli
• Diagnostic Markers: Intercellular bridges and keratin pearls present