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MUHS 2nd Year MBBS Pathology - Exam Answers (Easy Language)

Topics from your PDF (Johari Pathology):

Hashimoto Thyroiditis
Thyroid Carcinoma (Papillary, Follicular, Medullary, Anaplastic)
Squamous Cell Carcinoma of Skin
Melanoma
Osteosarcoma
Osteochondroma

TOPIC 1: HASHIMOTO THYROIDITIS

Q. Describe the pathogenesis of Hashimoto Thyroiditis. (Long Answer - 10 marks)

Definition: Hashimoto thyroiditis is a chronic autoimmune disease of the thyroid gland. The immune system attacks the thyroid, leading to hypothyroidism (reduced thyroid function). It is the most common cause of hypothyroidism in areas where iodine intake is adequate.

Epidemiology (Who gets it?)

Age: Peak between 45-65 years
Sex: More common in women (Female:Male = 10:1 to 20:1)
Also called: Chronic Lymphocytic Thyroiditis

Etiology (Cause)

It is an autoimmune disease - the body's own immune system wrongly attacks the thyroid.

Genetic factors:

Polymorphisms (changes) in genes that control immune regulation:
- CTLA4 gene (Cytotoxic T Lymphocyte-Associated Antigen-4)
- PTPN22 gene (Protein Tyrosine Phosphatase-22)
These same genetic changes are also seen in Graves' disease
Circulating antithyroid antibodies are found even in asymptomatic (symptom-free) siblings of patients

Pathogenesis (How does it happen?)

Simple Step-by-Step Explanation:

The disease starts with a failure of self-tolerance - meaning the immune system stops recognizing thyroid cells as "self" and starts attacking them.

Step 1 - Genetic trigger: Abnormalities in regulatory T-cells OR exposure of normally hidden thyroid antigens starts the process.

Step 2 - Autoimmunity starts:

CD4+ T-cells (helper cells) get activated and recognize thyroid antigens as foreign
They stimulate B-cells (plasma cells) which produce antithyroid antibodies (against thyroglobulin and thyroid peroxidase)
CD8+ cytotoxic T-cells directly kill thyroid cells (cell-mediated cytotoxicity)

Step 3 - Multiple damage mechanisms:

CD8+ cytotoxic T-cells - directly kill thyroid epithelial cells
Cytokines (like Interferon-gamma) - cause cytokine-mediated damage
NK cells - attach to antibodies on thyroid cells via Fc receptor → cause Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC)
Antithyroid antibodies produced by plasma cells further damage thyroid cells

Step 4 - End result: Progressive destruction of thyrocytes → replaced by mononuclear cell infiltration and fibrosis → Hypothyroidism

Morphology

Gross Appearance (What you see with naked eye):

Diffuse and symmetric enlargement of thyroid gland (goiter)
Gland is firm and nodular
Capsule is intact (well-demarcated from surrounding structures)
Cut surface: Pale, gray-tan with accentuation of normal lobulation

Microscopy (What you see under microscope):

Inflammation:
- Dense mononuclear inflammatory infiltrate = small lymphocytes + plasma cells in thyroid
- Lymphoid follicles with germinal centers (classic feature - looks like a lymph node)
Epithelial Changes:
- Atrophy of thyroid follicles - they appear smaller than normal
- Hurthle cell metaplasia (also called Askanazy cells / Oxyphil cells / Oncocytes):
  - Thyroid follicular cells transform into Hurthle cells
  - They have abundant eosinophilic (pink), granular cytoplasm
  - This is a metaplastic response to injury
Fibrosis - replacement of destroyed tissue

Key Points to Remember (Exam Mnemonics)

Feature	Detail
Most common cause of hypothyroidism	Yes (in iodine-sufficient areas)
Sex ratio	F:M = 10:1 to 20:1
Autoantibodies	Anti-thyroglobulin, Anti-TPO (Thyroid Peroxidase)
Key microscopy feature	Lymphoid follicles with germinal centers + Hurthle cells
Genes involved	CTLA4, PTPN22

TOPIC 2: THYROID CARCINOMA

Q. Write about different types of Thyroid Carcinoma with their features. (Long Answer - 10 marks)

Introduction: Thyroid carcinoma is a malignant tumor arising from thyroid cells. There are 4 main types:

Papillary Carcinoma (75-80%) - most common
Follicular Carcinoma (10-20%)
Medullary Carcinoma (5-7%)
Anaplastic Carcinoma (rarest)

A. PAPILLARY CARCINOMA (75-80%)

Definition: Most common thyroid cancer, arises from follicular cells, has papillary (finger-like) projections.

Risk Factors:

Radiation to the neck (most important)
Thyroglossal duct cyst

Cell of Origin: Follicular cell

Gross:

Cut surface is grayish-white, hard, scar-like (fibrotic)
Tumor has papillae-like projections (finger-like)

Microscopy (Most Important Features):

Branching papillae - well-formed finger-like projections with a fibrovascular core, covered by a single layer of tumor cells
"Orphan Annie Eye" nuclei (also called "ground glass nuclei"):
- The nuclei appear empty/clear/transparent - like the blank eyes of the cartoon character Annie
Nuclear grooves - fold/groove seen in the nucleus
Intranuclear inclusions - cytoplasm trapped inside the nucleus
Psammoma bodies - laminated (onion-skin) calcified concentric circles - very characteristic of papillary carcinoma

Diagnosis: FNAC (Fine Needle Aspiration Cytology)

Behavior: Spreads via lymphatics (lymph node spread common). Has good prognosis.

B. FOLLICULAR CARCINOMA (10-20%)

Cell of Origin: Follicular cell

Gross: Irregular thyroid gland enlargement, cut surface shows hemorrhage and necrosis

Microscopy:

Forms circular follicles (like normal thyroid but irregular)
No papillae present (important difference from papillary)
Hyperchromatic nuclei - cytoplasm resembles normal thyroid cells
Has calcification

Important feature: Distinguished from follicular adenoma (benign) ONLY by finding capsular or vascular invasion - this is the diagnostic hallmark!

Diagnosis: Biopsy (NOT FNAC, because you need to look for capsular invasion)

Behavior: Spreads via blood vessels (hematogenous spread) - to bone, lungs

C. MEDULLARY CARCINOMA (5-7%)

Cell of Origin: Parafollicular cells (C-cells) - NOT follicular cells

Key facts:

C-cells produce calcitonin (hormone that lowers calcium)
Can be sporadic (70%) or familial (30% - associated with MEN 2 syndrome)
RET gene mutation is seen

Gross: Invasion of adjacent soft tissue, trachea, esophagus

Microscopy:

Nests/trabeculae of round, spindle-shaped cells separated by fibrous septa
Amyloid deposition in stroma - most characteristic feature
- Pink homogenous extracellular deposits
- Stains with Congo red (amyloid)
Uniform hyperchromatic nuclei
Calcification present

Diagnosis: FNAC + Calcitonin levels (raised)

D. ANAPLASTIC CARCINOMA (Rarest - most aggressive)

Cell of Origin: Follicular cell (dedifferentiated)

Key facts:

Most aggressive thyroid cancer
Occurs in elderly patients
Very poor prognosis

Gross: Massive invasion of adjacent structures (trachea, esophagus, neck vessels, soft tissue)

Microscopy:

Various cell types - small cells, spindle cells, giant cells (pleomorphic)
Poorly differentiated
Abundant mitosis

Diagnosis: FNAC

Comparison Table (Very Important for Exam)

Feature	Papillary	Follicular	Medullary	Anaplastic
Frequency	75-80%	10-20%	5-7%	Rarest
Cell of origin	Follicular	Follicular	Parafollicular (C-cell)	Follicular
Spread	Lymphatics	Blood vessels	-	Local invasion
Key micro feature	Orphan Annie nuclei + Psammoma bodies	Follicles, no papillae	Amyloid in stroma	Pleomorphic cells
Diagnosis	FNAC	Biopsy	FNAC	FNAC
Gene	RET/PTC	RAS	RET	TP53
Prognosis	Best	Good	Moderate	Worst

TOPIC 3: SQUAMOUS CELL CARCINOMA OF SKIN

Q. Write the pathogenesis and morphology of Squamous Cell Carcinoma of Skin. (7-8 marks)

Definition: Squamous Cell Carcinoma (SCC) is the second most common malignant tumor arising on sun-exposed skin.

Sex: More common in men than women

Etiology and Risk Factors

Risk Factor	How it causes damage
UV light exposure	Produces DNA damage (most important)
Chronic immunosuppression	Reduced immune surveillance
Industrial carcinogens (Tars, oils)	Direct DNA damage
Chronic non-healing ulcers	Chronic irritation → malignant change
Old burn scars	Marjolin's ulcer
Ionizing radiation	DNA damage
Tobacco and betel nut chewing	For oral SCC

Pathogenesis

UV light → damages DNA → TP53 mutations (p53 is a tumor suppressor gene)
Loss of p53 → cells cannot repair DNA or undergo apoptosis
Dysregulated RAS signaling also contributes
Actinic keratosis = premalignant lesion (SCC in situ) → if untreated, becomes invasive SCC

Clinical Presentation

Appears as sharply defined, red, scaling plaques (early stage = SCC in-situ)
Invasive lesions: nodular growth that may ulcerate
Ulcer surrounded by a wide, elevated, indurated (hardened) border

Morphology

Gross:

Early: Red scaling plaques
Late/Invasive: Nodular growth with ulceration
Ulcer has elevated, hardened, irregular margins

Microscopy (Histology):

The tumor consists of irregular masses of epidermal cells that proliferate downward into the dermis.

Based on Differentiation:

Well-differentiated SCC:
- Polygonal squamous tumor cells arranged in orderly lobules
- Produce large amounts of keratin
- Form "Epithelial Pearls" or "Squamous Pearls" - laminated keratin whorls - very characteristic
- Intercellular bridges (desmosomes) visible
Moderately differentiated SCC:
- Anaplastic squamous cells
- Show single-cell keratinization = dyskeratosis (individual cells make keratin early)
- Fewer pearls
Poorly differentiated SCC:
- Very anaplastic cells
- No keratin pearls
- Requires immunohistochemistry for keratins to confirm diagnosis

Key Points

SCC is different from BCC (Basal Cell Carcinoma) - BCC is most common, SCC is second most common
SCC can metastasize (especially if on lip or ear) - unlike BCC
Squamous pearls = hallmark of well-differentiated SCC

TOPIC 4: MELANOMA

Q. Write the pathogenesis, morphology, and clinical features of Melanoma. (Long Answer - 10 marks)

Definition: Melanoma is a malignant tumor of melanocytes (pigment-producing cells). It is a relatively common and highly aggressive skin tumor.

Sites

Skin (most common): Trunk, leg, face, sole, palm, nail beds
Other sites: Oral and anogenital mucosa, esophagus, eye, substantia nigra (brain)
In men: most common on upper back
In women: most common on back and legs

Etiology and Risk Factors

Sun/UV Exposure: Most important factor
- Lightly pigmented individuals are at much greater risk than darkly pigmented individuals
Mutations in Tumor Suppressor Genes:
- CDKN2A gene encodes 3 tumor suppressors:
  - p15/INK4b
  - p16/INK4a
  - p14/ARF
- Loss of these → increased melanocytic proliferation + escape from senescence
- RB gene mutations also seen
Oncogene Activation:
- RAS is a normal signal transduction protein
- Mutated RAS or BRAF → activates RAS/RAF/MAP kinase cascade → cell proliferation
- These mutations promote cell growth and survival

Morphology - Growth Phases (Very Important)

Melanoma grows in TWO phases:

Phase 1: RADIAL GROWTH PHASE (Early)

Melanoma spreads horizontally within the epidermis and superficial dermis
Tumor cells lack capacity to metastasize at this stage
No metastasis risk

Phase 2: VERTICAL GROWTH PHASE (Late)

Tumor cells invade downward into deeper dermis
Develops clone of cells with metastatic potential
Risk of metastasis correlates with depth of invasion (measured from epidermal granular cell layer to deepest tumor cell)
Maturation of cells is absent in deep invasive portion

Microscopy

Tumor cells:
- Larger than normal melanocytes
- Large nuclei with irregular contours
- Chromatin clumping at periphery of nuclear membrane
- Prominent red (eosinophilic) nucleoli (very characteristic)
- Mitotic figures often seen
Pattern:
- Arranged in solid masses, sheets, islands
- Tumor invades upper epidermis AND deeper dermis
Melanin pigment:
- Present in cytoplasm as uniform brown fine granules
- Tumors without pigment = Amelanotic melanoma
Tumor-Infiltrating Lymphocytes (TILs):
- Lymphocytes seen surrounding the tumor (immune response)

Clinical Features

Usually asymptomatic
May present with itching or pain at lesion site

Changes in Pigmented Lesions - Warning Signs:

ABCD Rule of Melanoma (Must Remember!)

Letter	Feature	Melanoma	Benign Nevi
A	Asymmetry	Asymmetric	Symmetric
B	Border	Irregular, notched	Smooth, round
C	Color	Varied - black, brown, red, dark blue, gray	Uniform
D	Diameter	>10 mm (suspicious >6 mm)	Usually small

Note: Any pigmented lesion >6 mm in diameter, with change in appearance, or new onset itching/pain should raise suspicion of melanoma.

Prognosis

Depth of invasion (Breslow thickness) = most important prognostic factor
Superficial lesions (radial phase) = good prognosis
Deep lesions with vertical growth + lymph node spread = poor prognosis

TOPIC 5: OSTEOSARCOMA

Q. Describe the pathogenesis, morphology, and clinical features of Osteosarcoma. (Long Answer - 10 marks)

Definition: Osteosarcoma is a highly malignant bone tumor characterized by the formation of bone matrix or osteoid (unmineralized bone) by malignant tumor cells.

It is the most common primary malignant bone tumor in young people.

Epidemiology

Age: Bimodal distribution:
- Primary: 10-20 years (3/4 of all cases) - young people
- Secondary: >40 years (elderly, associated with pre-existing bone disease)
Sex: Boys > Girls (2:1 ratio)

Etiology and Pathogenesis

Primary Osteosarcoma (Young people):

Mutations in Tumor Suppressor Genes:
- RB gene (retinoblastoma gene) - most important
- TP53 gene mutations
Cell Cycle Regulators:
- MDM2 and CDK4 are overexpressed in many low-grade osteosarcomas
- These inhibit p53 and RB functions respectively → uncontrolled cell growth

Secondary Osteosarcoma (Elderly):

Pre-existing bone disorders:
- Paget's disease of bone
- Fibrous dysplasia
Previous chemotherapy:
- Children treated with alkylating agents for other malignancies have increased risk

Location

Arises in the metaphyseal region (near growth plate) of long bones of extremities
Most common sites:
- Lower femur (most common)
- Upper tibia or fibula
- Proximal humerus
In other words: tumors near the knee (lower femur + upper tibia) are most common, followed by shoulder (proximal humerus)

Morphology

Gross:

Usually big, bulky tumors
Cut surface: Gray-white in color, gritty (because of bone/osteoid formation)
Shows areas of hemorrhage and cystic degeneration
Intramedullary tumor extending up to epiphysis and also into soft tissue
Large destructive tan-white tumoral mass with poorly defined margins

Microscopy:

Single diagnostic feature = Production of osteoid or bone by malignant tumor cells

Malignant tumor cells:
- Vary in size and shape (pleomorphic)
- Large hyperchromatic nuclei (dark, enlarged)
- Frequent mitotic figures (including atypical mitoses)
- Bizarre tumor giant cells are common
Osteoid matrix:
- Appears as dense, uniform, eosinophilic (pink), glassy intercellular material
- This is unmineralized/noncalcified bone
Other features:
- Necrosis and hemorrhage
- Cartilage may also be present (chondroblastic type)

Clinical Features

Painful, progressively enlarging mass around knee or other involved site
Involved area is swollen and tender
Reduced function of adjacent joint
Serum alkaline phosphatase is elevated

Radiology (X-ray Appearance)

Codman Triangle:

Tumor infiltrates cortex and lifts the periosteum
Creates a space between cortex and lifted periosteum
On X-ray, this appears as a triangular shadow = Codman triangle

Sunburst Appearance:

When tumor extends into soft tissue, mineral deposits form parallel lines in periosteal region
This looks like rays of the sun = "sunburst" appearance

Summary of X-ray: Large destructive, mixed lytic (bone destruction) + blastic (neoplastic bone formation) mass with infiltrative margins

Classification of Osteosarcoma

Type	Location	Notes
Conventional (Central/Classic)	Intramedullary (inside bone cavity)	Most common
Low grade	On surface between cortex and periosteum	Less aggressive
Parosteal	Arises on bone surface, grows along external surface
Periosteal	Between cortex and periosteum	Pushes and lifts periosteum

By Histology:

Osteoblastic (bone-forming)
Chondroblastic (cartilage-forming)
Fibroblastic
Telangiectatic
Small cell
Giant cell

BONUS: OSTEOCHONDROMA (Short Note - 5 marks)

Q. Short note on Osteochondroma

Definition: Osteochondroma is the most common benign bone tumor. It is a bony outgrowth capped with cartilage.

Site/Location:

Metaphysis (near growth plate of long bone) - same site as osteosarcoma but BENIGN
Mushroom-shaped lesions, 1-20 cm in size

Gross:

Mushroom-shaped bony outgrowth
Cap is composed of benign hyaline cartilage (important - it is benign)

Pathogenesis:

Genetic alteration of EXT1 and EXT2 genes (Exostosin genes)
These are tumor suppressor genes involved in cartilage formation

Key Facts:

Can be solitary or multiple (multiple hereditary exostoses = familial form)
Usually asymptomatic, found incidentally
Small risk of malignant transformation to chondrosarcoma (if the cartilage cap grows after skeletal maturity)

QUICK REVISION TABLE - All Topics

Disease	Key Pathogenesis	Key Micro Feature	Key Clinical Point
Hashimoto Thyroiditis	Autoimmune - T cell + antibody mediated	Lymphoid follicles + Hurthle cells	Hypothyroidism, women F:M=10:1
Papillary Thyroid Ca	Radiation exposure, RET/PTC mutation	Orphan Annie nuclei + Psammoma bodies	Most common thyroid Ca (75-80%), lymphatic spread
Follicular Thyroid Ca	RAS mutation	Follicles, NO papillae, capsular invasion	Diagnosed by biopsy, blood-borne spread
Medullary Thyroid Ca	RET mutation, from C-cells	Amyloid in stroma	Associated with MEN 2
Anaplastic Thyroid Ca	TP53 mutation	Pleomorphic cells	Most aggressive, elderly
SCC Skin	UV light → TP53 mutation	Squamous pearls (keratin whorls)	2nd most common skin cancer
Melanoma	UV light, BRAF/RAS mutation	Prominent red nucleoli, vertical growth	ABCD rule, depth = prognosis
Osteosarcoma	RB + TP53 mutations	Osteoid produced by malignant cells	10-20 yrs, knee region, Codman triangle + sunburst X-ray
Osteochondroma	EXT1/EXT2 mutation	Hyaline cartilage cap	Most common benign bone tumor

Exam Tips:

Hashimoto: Always mention CTLA4 + PTPN22 genes, Hurthle cells, and the 3 mechanisms of damage (CD8 cytotoxicity, cytokines, ADCC)
Papillary Ca: Orphan Annie nuclei + Psammoma bodies = must write in every answer
Melanoma: ABCD rule + two growth phases (radial then vertical) = must write
Osteosarcoma: Codman triangle + sunburst = must write for X-ray section
SCC: Squamous/Epithelial pearls = hallmark of well-differentiated SCC

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