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Pathology Practical Slides - Detailed Explanations

HISTOPATHOLOGY SLIDES

1. Fatty Liver (Hepatic Steatosis)

Stain: H&E

Gross: Enlarged, yellow, greasy liver.

Microscopy - What to say:

Hepatocytes show large, clear, sharply defined vacuoles in the cytoplasm that displace the nucleus to the periphery ("signet ring" appearance) - this is macrovesicular steatosis
In acute/toxic cases, small droplets surround the nucleus - microvesicular steatosis
No significant inflammation or fibrosis in simple steatosis
Centrilobular distribution in alcoholic fatty liver; panlobular in obesity/diabetes

Causes: Alcohol (most common), obesity, diabetes mellitus, pregnancy (acute fatty liver of pregnancy - microvesicular), drugs (tetracycline, valproate)

Key point: Fat stains (Oil Red O on frozen section) confirm lipid. On H&E the vacuoles appear empty because fat dissolves during processing.

2. Monckeberg Medial Calcific Sclerosis

Stain: H&E (calcium stains blue-purple; Von Kossa stain confirms)

Gross: "Pipestem" or "eggshell" arteries - hard, calcified, non-compressible vessels.

Microscopy - What to say:

Medium-sized muscular arteries (radial, ulnar, femoral, tibial)
Calcific deposits in the tunica media, specifically centered on the internal elastic lamina
The deposits appear as basophilic (dark blue-purple) irregular plaques in the media
Lumen is NOT narrowed - key distinguishing feature from atherosclerosis
No intimal plaque, no lipid, no inflammatory cells
The media may show "egg-shell" calcification in a ring pattern

Key distinction: Unlike atherosclerosis (intimal), Monckeberg affects the media. Unlike arteriolosclerosis (small vessels), this affects medium vessels. It does NOT cause ischemia directly.

Occurs in: People >50 years, diabetics, chronic kidney disease patients.

3. Acute Appendicitis

Stain: H&E

Gross: Swollen, congested appendix with fibrinous exudate on serosa.

Microscopy - What to say:

Transmural neutrophilic infiltration - neutrophils in all layers (mucosa, submucosa, muscularis, serosa)
Mucosal ulceration with fibrinopurulent exudate in the lumen
Vascular congestion and edema in the submucosa
Diagnostic hallmark: neutrophils within the muscularis propria
Periappendiceal fat may show edema and acute inflammation
In gangrenous appendicitis: areas of necrosis/coagulative necrosis visible

Pathogenesis: Obstruction (fecalith, lymphoid hyperplasia) → bacterial overgrowth → mucosal invasion → transmural spread.

Clinical: RIF pain, fever, raised WBC, positive McBurney's point tenderness.

4. Lobar Pneumonia

Stain: H&E

Gross: Entire lobe affected; appearance depends on stage.

Microscopy - What to say (4 classical stages):

Stage	Duration	Gross	Microscopy
Congestion	Day 1-2	Red, heavy	Alveolar capillary engorgement, proteinaceous fluid, few bacteria, rare neutrophils
Red Hepatization	Day 2-4	Red, airless, liver-like	Alveoli filled with RBCs, neutrophils, fibrin strands; "hepatized" lung
Grey Hepatization	Day 4-8	Grey, firm	RBCs lysed; alveoli filled with fibrin, neutrophils, macrophages
Resolution	Day 8+	Returning to normal	Enzymatic digestion of fibrin; macrophage-dominant; alveolar architecture restored

Causative organism: Streptococcus pneumoniae (most common)

Key point: Alveolar architecture is preserved throughout (unlike ARDS). Interalveolar pores of Kohn allow spread to entire lobe.

5. Granulation Tissue

Stain: H&E

Gross: Pink-red, granular, moist tissue at base of healing wound.

Microscopy - What to say (the "3 pillars"):

Proliferating capillaries (angiogenesis): New thin-walled capillaries, often cut in cross-section giving Swiss-cheese appearance; endothelial cells plump and active
Proliferating fibroblasts: Spindle-shaped cells with pale cytoplasm; producing collagen
Inflammatory infiltrate: Predominantly macrophages, lymphocytes, plasma cells; some neutrophils early

Edematous, loose connective tissue stroma
Myofibroblasts present (contribute to wound contraction)
Over time: fibroblasts replace capillaries → scar (fibrosis)

Growth factors: VEGF (angiogenesis), PDGF, TGF-β, FGF (fibroblast proliferation)

6. TB Lymph Node (Tuberculous Lymphadenitis)

Stain: H&E; ZN stain for acid-fast bacilli

Gross: Enlarged, matted lymph node; cut section shows white/yellow caseous material ("cheesy" necrosis).

Microscopy - What to say:

Epithelioid granulomas - collections of epithelioid macrophages (large, pale, "shoe sole" nuclei) with abundant pale cytoplasm
Langhans giant cells: Large multinucleated cells with nuclei arranged in a horseshoe/peripheral arc pattern at one pole
Caseous (cheesy) necrosis at center of granuloma: amorphous, acellular, eosinophilic material ("nuclear dust" - structureless)
Peripheral rim of lymphocytes
Fibrous capsule around granuloma (older lesions)

ZN stain: Red acid-fast bacilli on blue background (may be sparse - often negative despite active TB)

Caseous necrosis is pathognomonic of TB (though rarely seen in other conditions like histoplasmosis)

7. Actinomycosis

Stain: H&E; Gram stain (Gram-positive filaments)

Gross: Yellow sulfur granules in pus; indurated fibrotic tissue.

Microscopy - What to say:

"Sulfur granules" - the pathognomonic finding: basophilic central mass of tangled filaments
Peripheral club-shaped, eosinophilic projections ("clubs" or "rosette" pattern around granule) - this is the Splendore-Hoeppli phenomenon
Surrounding acute and chronic inflammation (neutrophils, macrophages, giant cells)
Dense fibrosis ("wooden" consistency grossly)
Draining sinuses may be seen

Organism: Actinomyces israelii - a Gram-positive, filamentous, anaerobic bacterium (part of normal oral flora)

Sites: Cervicofacial (most common - "lumpy jaw"), thoracic, abdominal (after appendiceal rupture), pelvic (IUD-associated)

8. Rhinosporidiosis

Stain: H&E; PAS stain highlights the sporangia

Gross: Polypoid, friable, vascular masses in the nasal cavity; "strawberry-like" or sessile polyps.

Microscopy - What to say:

Large sporangia (300-400 μm diameter) - thick-walled, round structures in the submucosa
Each sporangium contains thousands of endospores (sporangiospores)
Sporangia at various stages: immature (small, pale) to mature (large, packed with spores)
Mature sporangia rupture releasing spores into surrounding tissue
Surrounding stroma shows edema, vascular congestion, mixed inflammatory infiltrate (lymphocytes, plasma cells, eosinophils, neutrophils)
Overlying hyperplastic squamous or respiratory epithelium

Organism: Rhinosporidium seeberi (now classified as a mesomycetozoan, not a true fungus)

Endemic in: India (especially Tamil Nadu, Kerala), Sri Lanka

9. Lipoma

Stain: H&E

Gross: Soft, encapsulated, yellow fatty tumor.

Microscopy - What to say:

Composed of mature adipocytes - large cells with single large clear cytoplasmic vacuole pushing nucleus to periphery (signet-ring appearance)
Cells are uniform in size and shape - no nuclear atypia, no mitoses
Thin fibrous capsule surrounding the tumor
Thin fibrovascular septa dividing the lobules
Identical to normal fat histologically - diagnosis requires clinical/gross correlation

Distinguish from:

Liposarcoma: lipoblasts (cells with multiple small vacuoles indenting the nucleus), nuclear atypia, mitoses
Lipoblastoma (children): immature fat cells, myxoid stroma

10. Capillary Hemangioma

Stain: H&E

Gross: Bright red, compressible, lobulated lesion; commonly in skin/subcutis of children.

Microscopy - What to say:

Lobular proliferation of small, thin-walled capillary-sized vessels
Vessels lined by plump, proliferating endothelial cells - may be so cellular that lumina are nearly absent in early lesions
Vessels contain RBCs
Thin pericyte layer around vessels
Lobules separated by loose fibrous stroma
In early (cellular) phase: endothelial cells dominant; in late phase: vessels well-formed, lumina open
No nuclear atypia or significant mitotic activity

Types:

Strawberry hemangioma (infantile): grows rapidly then involutes
Cherry angioma: adults, dermal

11. Schwannoma (Neurilemmoma)

Stain: H&E; S-100 protein positive on IHC

Gross: Encapsulated, firm, whitish nerve sheath tumor; eccentrically placed on nerve.

Microscopy - What to say (the biphasic pattern):

Antoni A areas: Densely cellular; spindle cells with elongated, wavy nuclei arranged in palisading rows ("Verocay bodies") - parallel rows of nuclei with anuclear zones between them
Antoni B areas: Loosely arranged, hypocellular; myxoid/edematous matrix; cells haphazardly arranged; sometimes microcysts and hemorrhage

Encapsulated tumor - key feature distinguishing from neurofibroma
Thick-walled hyalinized vessels
Hemosiderin deposits (due to old hemorrhage)
No true nerve fibers within the tumor (nerve displaced to capsule)

S-100 positive throughout (unlike neurofibroma where only some cells stain)

12. Squamous Cell Carcinoma (SCC)

Stain: H&E

Gross: Ulcerated or fungating mass with indurated edges.

Microscopy - What to say:

Irregular islands/nests of malignant squamous cells invading the dermis/stroma
Keratin pearls (epithelial pearls): Concentric whorls of keratinizing squamous cells with central pink amorphous keratin - pathognomonic of well-differentiated SCC
Individual cell keratinization (dyskeratosis) - pink cytoplasm with pyknotic nucleus
Intercellular bridges (desmosomes) between cells
Nuclear pleomorphism, hyperchromatism, prominent nucleoli
Mitotic figures (normal and abnormal)
Desmoplastic stromal reaction
Surrounding chronic inflammatory infiltrate

Grades: Well-differentiated (many keratin pearls) → Poorly differentiated (few pearls, more anaplasia)

13. Adenocarcinoma Colon

Stain: H&E

Gross: Polypoid or ulcerating mass in colon; "napkin ring" constriction in left colon.

Microscopy - What to say:

Malignant glands infiltrating through the bowel wall (muscularis propria, subserosa)
Irregular glandular structures lined by columnar cells with nuclear stratification, pleomorphism, hyperchromatism
Mucin secretion (intraluminal or intracellular - signet ring cells if mucin displaces nucleus)
Loss of normal polarity; nuclei at different levels
Mitotic figures, prominent nucleoli
Desmoplastic stroma (abundant fibrous reaction around glands)
Tumor necrosis ("dirty necrosis") within gland lumina - characteristic of colorectal adenocarcinoma
May invade lymphatics, blood vessels, perineural spaces

Grading: Well (>95% gland formation), Moderate (50-95%), Poor (<50%) or undifferentiated

14. Pleomorphic Adenoma (Mixed Tumor of Salivary Gland)

Stain: H&E

Gross: Firm, encapsulated, bosselated (lobulated) tumor; cut section white/translucent with cartilaginous areas.

Microscopy - What to say (the "mix" is the key):

Epithelial component: Islands, ducts, nests, and sheets of epithelial cells (duct-forming inner cells + myoepithelial outer cells)
Mesenchymal (stromal) component: Myxoid, chondroid (cartilage-like), or even osseous areas - derived from myoepithelial cells
Both components mixed intimately within the same tumor
Incomplete fibrous capsule (important - can lead to recurrence if not excised completely)
Pseudopods/satellite nodules through capsule

"Pleomorphic" = diverse tissue types, NOT nuclear pleomorphism

Malignant transformation: Carcinoma ex pleomorphic adenoma (in ~5% of long-standing cases)

15. Atherosclerosis

Stain: H&E; Masson's trichrome (for collagen); Oil Red O (for lipid in frozen sections)

Gross: Intimal plaques - early (fatty streaks) → fibrous plaques → complicated plaques (calcification, ulceration, thrombosis).

Microscopy - What to say:

Fibrous cap: Dense collagen, smooth muscle cells, and scattered foam cells
Atheromatous core (necrotic core): Amorphous, acellular debris; cholesterol clefts (needle-shaped spaces left after fat dissolves); extracellular lipid
Foam cells: Lipid-laden macrophages with pale, foamy cytoplasm (also smooth muscle cells can form foam cells)
Calcification in older plaques (basophilic deposits)
Intimal thickening - smooth muscle cell proliferation
Vasa vasorum proliferation in adventitia
Neovascularization in plaque (intraplaque hemorrhage risk)
Disrupted/lost internal elastic lamina (visible on elastic stains)

16. Renal Cell Carcinoma (RCC)

Stain: H&E

Gross: Upper pole mass; yellow (lipid-rich), variegated (hemorrhage, necrosis); pseudocapsule.

Microscopy - What to say (Clear Cell RCC - most common ~75%):

Large polygonal cells with abundant clear cytoplasm (glycogen and lipid dissolved in processing)
Small, round, centrally placed nucleus
Arranged in solid nests, tubules, and acinar patterns
Prominent thin-walled sinusoidal vasculature between nests (delicate chicken-wire vascularity)
Nuclei may be bland (low-grade) to pleomorphic (high-grade)
Hemorrhage and necrosis common

Key associations: 3p deletion, VHL gene mutation (sporadic); VHL syndrome (familial)

Triad: Flank pain + hematuria + palpable mass (late presentation)

17. Benign Prostatic Hyperplasia (BPH)

Stain: H&E

Gross: Enlarged, nodular prostate; encucleated with rubbery nodules; predominant in transition zone.

Microscopy - What to say:

Nodular hyperplasia of both glandular and stromal elements
Large, irregular glands with papillary infoldings and intraluminal bridging; lined by two cell layers: inner tall columnar secretory cells + outer basal cells
Corpora amylacea (amyloid bodies): round, laminated, pink concentric structures within gland lumina - concentric calcified secretions
Stromal nodules: proliferating smooth muscle and fibrous tissue
No nuclear atypia, no infiltrative growth (benign)
May show foci of squamous metaplasia

Mechanism: DHT-mediated (5-alpha reductase converts testosterone to DHT); estrogen increases DHT receptors

18. Leiomyoma (Fibroid)

Stain: H&E; Masson's trichrome (collagen = blue)

Gross: Well-circumscribed, firm, whorled white nodule(s) in uterus; multiple common.

Microscopy - What to say:

Interlacing bundles of smooth muscle cells in various directions (whorled pattern)
Cells are elongated/fusiform with abundant eosinophilic (pink) cytoplasm
Cigar-shaped (blunt-ended) nuclei - no atypia, no mitoses (or rare)
Well-demarcated from surrounding myometrium (compressed rim of uterine muscle at periphery)
Variable amount of fibrous stroma between muscle bundles
Degenerative changes: hyaline degeneration (most common), myxoid, cystic, red/carneous (hemorrhagic infarction in pregnancy), calcification

Estrogen-dependent - grows in reproductive age, regresses after menopause

19. Hydatidiform Mole

Stain: H&E

Gross (Complete mole): Bunch-of-grapes appearance; no fetal parts.

Microscopy - What to say:

Complete Mole:

Hydropic (edematous) chorionic villi - large, swollen, fluid-filled villi with central cisterns (acellular spaces)
Trophoblastic proliferation (both cytotrophoblast and syncytiotrophoblast) circumferential/diffuse around all villi
Absence of blood vessels in villi
No fetal/embryonic tissue

Partial Mole:

Two populations of villi: some normal, some hydropic (smaller than complete mole)
Scalloped/irregular outline of villi ("fjord-like" invaginations of trophoblast)
Focal trophoblastic hyperplasia
Fetal tissue/RBCs present

Key risk: Complete mole has 2-3% risk of choriocarcinoma. Monitor beta-hCG.

20. Fibroadenoma

Stain: H&E

Gross: Well-encapsulated, rubbery, mobile ("breast mouse"), white/grey tumor.

Microscopy - What to say:

Both epithelial and stromal components (benign biphasic tumor)
Ducts (epithelial component): Round or compressed slit-like ductal structures lined by two layers (inner epithelial + outer myoepithelial)
Fibrous stroma: Hypercellular, myxoid fibrous tissue surrounding the ducts
Two architectural patterns:
- Intracanalicular: Stroma compresses ducts into elongated slits (leaf-like pattern)
- Pericanalicular: Stroma surrounds open round ducts concentrically
No atypia, rare mitoses, encapsulated

Most common breast tumor in young women (<30 years)

21. Multinodular Goitre (MNG)

Stain: H&E

Gross: Markedly enlarged, asymmetric thyroid with multiple nodules; cut section shows colloid-filled nodules, areas of hemorrhage, fibrosis.

Microscopy - What to say:

Variably-sized follicles - some markedly distended with colloid, others small and hyperplastic
Flattened follicular epithelium in large colloid-filled follicles
Foci of follicular hyperplasia: tall columnar epithelium with papillary infoldings
Degenerative changes: Hemorrhage (hemosiderin-laden macrophages), fibrosis, calcification, cystic change
No significant nuclear atypia (no Orphan Annie nuclei)
Colloid appears as homogeneous eosinophilic material; "scalloping" at periphery in active follicles

Iodine deficiency is the most common worldwide cause.

22. Papillary Thyroid Carcinoma (PTC)

Stain: H&E

Gross: Irregular, firm, whitish mass; calcified foci; often multifocal.

Microscopy - What to say:

Papillary architecture: Finger-like projections with fibrovascular stalks lined by neoplastic epithelium
Nuclear features (most important for diagnosis - even without papillae):
- "Orphan Annie eye" nuclei: Large, oval, optically clear ("empty-looking") nuclei with pale/powdery chromatin
- Nuclear grooves: Linear longitudinal infoldings of nuclear membrane
- Nuclear pseudoinclusions: Cytoplasmic invaginations appearing as pink intranuclear inclusions
Psammoma bodies: Concentric calcified laminated structures (50%) - virtually pathognomonic of PTC
Follicular variant: follicular architecture but same nuclear features
Lymph node metastasis common (lymphotropic)

BRAF V600E mutation in ~60% of cases. Best prognosis among thyroid malignancies.

23. Liver Cirrhosis

Stain: H&E; Masson's trichrome (collagen = blue, best for fibrosis); Reticulin stain

Gross: Small, shrunken, nodular liver with firm fibrotic texture.

Microscopy - What to say:

Regenerative nodules: Rounded clusters of hepatocytes separated by fibrous bands; hepatocytes in regenerative nodules show disturbed architecture (thickened plates, pseudoacini)
Fibrous septa (bands): Broad bands of fibrous tissue linking portal tracts to central veins ("bridging fibrosis") and portal tract to portal tract
Loss of normal lobular architecture
Bile duct proliferation at periphery of nodules (ductular reaction)
Mixed inflammatory infiltrate in septa
Features of underlying etiology may be present: Mallory-Denk bodies (alcohol), steatosis (NASH), bile stasis (PBC)

On Masson's trichrome: Fibrous septa stain bright blue, regenerative nodules appear red/brown.

24. Seminoma Testis

Stain: H&E; PLAP and OCT4 positive on IHC

Gross: Homogeneous, creamy white, lobulated tumor filling the testis.

Microscopy - What to say:

Large, uniform polygonal cells arranged in sheets, nests, or lobules divided by delicate fibrovascular septa
Cells have: large, centrally placed nuclei with prominent nucleoli; clear cytoplasm (rich in glycogen - PAS positive)
Fibrous septa containing lymphocytic infiltrate (T-lymphocytes) - this is characteristic and helps distinguish from embryonal carcinoma
Granulomatous reaction (epithelioid granulomas, giant cells) in ~50% of cases
No embryoid bodies (unlike embryonal carcinoma)
Well-defined cell borders

Tumor marker: Beta-hCG mildly elevated in ~15% (syncytiotrophoblasts); AFP is NOT elevated (elevation suggests non-seminomatous element).

Most common testicular tumor in 30-40 year olds. Exquisitely radiosensitive.

25. Basal Cell Carcinoma (BCC)

Stain: H&E

Gross: Pearly, rolled edges with central ulceration ("rodent ulcer"); sun-exposed skin, especially face/nose.

Microscopy - What to say:

Nests and cords of basaloid cells arising from the basal layer of the epidermis
Cells: small, scant cytoplasm, oval dark-staining nuclei, no prominent nucleoli, high N:C ratio
Peripheral palisading: Cells at the periphery of nests arranged in a neat row with nuclei parallel (like a picket fence)
Retraction artifact: Cleft (shrinkage artifact) between tumor nests and surrounding stroma - highly characteristic
Desmoplastic stroma (mucinous/myxoid stroma in nests)
Mitotic figures present but usually not atypical
Connection to overlying epidermis

Most common skin cancer in humans. Local invasion but rarely metastasizes ("basal-cell never goes to lymph nodes" is a teaching point).

26. Chronic Cholecystitis

Stain: H&E

Gross: Thick-walled gallbladder; stones often present; mucosal surface may show green bile staining.

Microscopy - What to say:

Rokitansky-Aschoff sinuses: Mucosal herniation/outpouching deep into the muscular layer - pathognomonic
Chronic inflammatory infiltrate: Lymphocytes, plasma cells, occasional eosinophils in the lamina propria and submucosa
Fibrosis: Thickening of the muscularis and subserosa
Mucosal folds may be flattened or atrophic
Cholesterol polyps (xanthogranulomatous foci): foamy macrophages laden with lipid
Metaplasia: intestinal (goblet cells) or gastric (pyloric) metaplasia of mucosa

Key finding = Rokitansky-Aschoff sinuses + chronic inflammation + fibrosis

27. CVC Lung (Chronic Venous Congestion of Lung)

Stain: H&E; Prussian blue (for hemosiderin)

Gross: "Brown induration" - firm, brown lung due to hemosiderin + fibrosis.

Microscopy - What to say:

Hemosiderin-laden macrophages ("heart failure cells") within alveolar spaces - macrophages stuffed with brown granular hemosiderin pigment (from phagocytosed RBCs that leaked from engorged capillaries)
Dilated and congested alveolar capillaries and pulmonary veins
Interstitial fibrosis: Thickening of alveolar walls and interlobular septa
Alveolar spaces may contain pink transudate (edema) and desquamated macrophages
Hemosiderin also in interstitium

On Prussian Blue stain: Hemosiderin stains bright blue, confirming nature of pigment.

Cause: Left heart failure (mitral stenosis most classic cause)

28. Caseous Necrosis

Stain: H&E

Gross: Soft, cheesy, white-yellow material (resembles crumbled cheese).

Microscopy - What to say:

Amorphous, acellular, eosinophilic (pink) material - all cellular detail is completely lost (unlike coagulative necrosis where ghost outlines remain)
No nuclear remnants, no architectural outlines - completely structureless
The necrotic material has a "granular, cheesy" appearance at low power
Surrounded by epithelioid granuloma: epithelioid macrophages, Langhans giant cells, lymphocytes
Central caseous zone + peripheral granulomatous reaction = tuberculous granuloma

Pathognomonic for TB (also seen in other mycobacterial infections, histoplasmosis, sarcoidosis rarely)

Mechanism: Cell-mediated immunity (Type IV hypersensitivity) causes macrophage activation; partially effective killing leads to caseous rather than complete resolution.

29. Mucinous Cystadenoma

Stain: H&E; Mucicarmine/Alcian blue (confirms mucin)

Gross: Large multilocular cyst; ovary (most common); each locule contains thick, viscid mucus.

Microscopy - What to say:

Multilocular cysts lined by a single layer of tall columnar mucin-secreting epithelial cells
Cells resemble endocervical or intestinal-type epithelium; goblet cells often present
Nuclei basally placed, no significant atypia, rare mitoses (benign)
Abundant intracellular and intraluminal mucin (pale blue/grey on H&E; bright red on mucicarmine)
Thin fibrous stroma between locules
No papillary projections or solid areas (if present - borderline or malignant)

Risk: Rupture → pseudomyxoma peritonei (mucinous deposits throughout peritoneum)

30. Cavernous Hemangioma

Stain: H&E

Gross: Bluish-red, sponge-like lesion; common in liver; bleeds profusely when cut.

Microscopy - What to say:

Large, dilated, thin-walled vascular spaces (cavernous channels)
Channels lined by a single layer of flat (attenuated) endothelial cells - no proliferating or plump cells
Channels filled with RBCs or organizing thrombus (phleboliths - organized calcified thrombi)
Thin fibrous walls between channels
No smooth muscle layer (unlike normal veins)
Stroma may show hemosiderin deposits and fibrous scarring
Low-power appearance: "Swiss cheese" or sponge-like pattern with large blood-filled spaces

Distinguish from capillary hemangioma: Capillary = small vessels, plump endothelium, lobular; Cavernous = large dilated channels, flat endothelium.

31. Osteoclastoma (Giant Cell Tumor of Bone)

Stain: H&E

Gross: Eccentric, lytic lesion at the epiphysis of long bones; "soap-bubble" appearance on X-ray; may be red-brown and hemorrhagic ("brown tumor" appearance).

Microscopy - What to say:

Mononuclear stromal cells (key diagnostic cells): Oval to spindle-shaped cells with round/oval nuclei and moderate cytoplasm; scattered mitoses; nuclei resemble those in osteoclast-like giant cells
Multinucleated giant cells (osteoclast-like): Evenly distributed throughout the tumor; enormous cells with 20-100 uniformly distributed nuclei (important: nuclei identical to stromal cell nuclei - same morphology); prominent nucleoli; abundant eosinophilic cytoplasm
Hemosiderin deposits (brown pigment)
Areas of hemorrhage and necrosis
Reactive woven bone at periphery
No significant pleomorphism in giant cell nuclei

Location: Epiphysis of long bones (distal femur, proximal tibia, distal radius) in skeletally mature patients (20-40 years)

Behavior: Locally aggressive, 2-5% metastasize to lung despite benign histology.

HEMATOLOGY SLIDES

1. Microcytic Hypochromic Anemia

Stain: Leishman/Giemsa stain (peripheral blood smear)

What to say on PBS:

RBCs are smaller than normal (smaller than lymphocyte nucleus - microcytic)
Central pallor is enlarged (>1/3 of cell diameter - hypochromic; normally pallor = 1/3 diameter)
Cells may appear as "ring forms" with just a thin rim of hemoglobin
Anisocytosis: variation in size; Poikilocytosis: variation in shape
Target cells (codocytes): Bull's-eye appearance; seen in thalassemia, liver disease, hemoglobin C
Pencil/cigar cells: Elongated RBCs - classic for iron deficiency anemia
In thalassemia: nucleated RBCs, basophilic stippling, target cells prominent

Causes:

Iron Deficiency Anemia (most common): Low serum iron, low ferritin, high TIBC; pencil cells, koilonychia clinically
Thalassemia: Low/normal iron, low MCV, normal/high RBC count; target cells, basophilic stippling
Sideroblastic anemia, Anemia of chronic disease (usually normocytic but can be microcytic)

Labs: MCV <80 fL; MCH <27 pg; MCHC <32 g/dL

2. Eosinophilia

Stain: Leishman stain

What to say on PBS:

Increased eosinophils (>0.5 × 10⁹/L or >5% of differential)
Eosinophils identified by: bilobed nucleus + large, coarse, bright orange-red (eosinophilic) granules that fill the cytoplasm
Granules are uniform in size; refractile appearance
May see toxic granulation or vacuolation in severe cases

Grading:

Mild: 0.5-1.5 × 10⁹/L
Moderate: 1.5-5 × 10⁹/L
Severe (Hypereosinophilia): >5 × 10⁹/L

Causes (NAACP mnemonic):

Neoplasms (lymphoma, leukemia, solid tumors)
Allergy/Atopy (asthma, eczema, hay fever) - most common in developed world
Addison's disease, autoimmune
Collagen vascular disease
Parasites (helminths - Ascaris, Toxocara, Filaria) - most common worldwide

3. Chronic Myeloid Leukemia (CML)

Stain: Leishman stain

What to say on PBS:

Leukocytosis: WBC markedly elevated (often 50,000-200,000/μL)
Left shift: Complete spectrum of myeloid maturation visible - myeloblasts, promyelocytes, myelocytes, metamyelocytes, bands, mature neutrophils ("myelocyte bulge" at myelocyte stage)
Basophilia - increased basophils (important clue; basophils have dark purple granules, bilobed/irregular nucleus)
Eosinophilia also seen
Thrombocytosis (platelets increased) in chronic phase
Low Leukocyte Alkaline Phosphatase (LAP) score - differentiates from leukemoid reaction (where LAP is high)
Myeloblasts <10% in chronic phase; >20% = blast crisis (transformation to AML/ALL)

Key genetic feature: Philadelphia chromosome - t(9;22) translocation → BCR-ABL fusion gene → constitutively active tyrosine kinase → uncontrolled proliferation

Treatment: Imatinib (Gleevec) - BCR-ABL tyrosine kinase inhibitor - transformed prognosis

4. Chronic Lymphoid (Lymphocytic) Leukemia (CLL)

Stain: Leishman stain

What to say on PBS:

Lymphocytosis: Marked increase in small, mature-appearing lymphocytes (WBC 20,000-200,000/μL)
Lymphocytes: small, scant cytoplasm, round, condensed (clumped) "soccer-ball" chromatin, no visible nucleoli
Smudge cells (basket cells): Crushed lymphocytes with smeared nuclear material - pathognomonic of CLL; occur because CLL cells are fragile
Occasional "prolymphocytes" (larger cells with prominent nucleolus)
Normal or reduced RBCs (anemia if advanced)
Thrombocytopenia may be present

Immunophenotype: CD5+ CD19+ CD23+ (co-expression of B-cell marker CD19 with T-cell marker CD5 is characteristic)

Most common leukemia in adults in Western countries. "Disease of the elderly." Indolent course. May develop autoimmune hemolytic anemia (Coombs positive).

Staging (Rai): 0 (lymphocytosis only) to IV (with anemia/thrombocytopenia)

Quick Revision Summary Table

#	Slide	Key Diagnostic Feature
1	Fatty Liver	Clear cytoplasmic vacuoles displacing nucleus
2	Monckeberg Sclerosis	Medial calcification, lumen preserved
3	Acute Appendicitis	Transmural neutrophilic infiltration
4	Lobar Pneumonia	4 stages; alveoli filled with fibrin/cells
5	Granulation Tissue	New capillaries + fibroblasts + inflammation
6	TB Lymph Node	Epithelioid granuloma + Langhans cells + caseous necrosis
7	Actinomycosis	Sulfur granules with clubs (Splendore-Hoeppli)
8	Rhinosporidiosis	Large sporangia with endospores
9	Lipoma	Mature adipocytes, encapsulated, no atypia
10	Capillary Hemangioma	Lobular small vessels, plump endothelium
11	Schwannoma	Antoni A (Verocay bodies) + Antoni B
12	SCC	Keratin pearls + intercellular bridges
13	Adenocarcinoma Colon	Malignant glands + dirty necrosis
14	Pleomorphic Adenoma	Epithelial + chondromyxoid stroma
15	Atherosclerosis	Intimal plaque: fibrous cap + necrotic core + foam cells
16	RCC	Clear cells + delicate vascularity
17	BPH	Glandular hyperplasia + corpora amylacea
18	Leiomyoma	Interlacing smooth muscle, cigar nuclei
19	Hydatidiform Mole	Hydropic villi + trophoblastic proliferation
20	Fibroadenoma	Ducts in fibrous stroma; intracanalicular/pericanalicular
21	MNG	Variable follicle size, colloid, degenerative changes
22	Papillary Thyroid Ca	Orphan Annie nuclei + psammoma bodies
23	Liver Cirrhosis	Regenerative nodules + fibrous bands
24	Seminoma	Sheets of clear cells + lymphocytic septa
25	BCC	Basaloid nests + peripheral palisading + retraction
26	Chronic Cholecystitis	Rokitansky-Aschoff sinuses + chronic inflammation
27	CVC Lung	Heart failure cells (hemosiderin macrophages)
28	Caseous Necrosis	Acellular eosinophilic debris + granuloma
29	Mucinous Cystadenoma	Multilocular cysts, mucin-secreting columnar cells
30	Cavernous Hemangioma	Large dilated channels, flat endothelium
31	Osteoclastoma	Uniform osteoclast-like giant cells + mononuclear stroma
H1	Microcytic Hypochromic	Small RBCs, enlarged pallor, pencil cells
H2	Eosinophilia	Increased eosinophils with orange granules
H3	CML	All myeloid stages + basophilia + Philadelphia chr.
H4	CLL	Mature lymphocytosis + smudge cells

Exam Tips:

Always describe what you see at low power first (overall architecture), then high power (cellular details)
Start every slide description with the stain used
For practical viva: state the diagnosis, then give 2-3 key histological features that confirm it
For carcinomas: mention grade (differentiation) and any invasion you see

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