General Pathology — MCQs

General Pathology Indian Medical PG Practice Questions and MCQs

Question 421: Neurofibromatosis is associated with all of the following except?

A. Autosomal recessive inheritance (Correct Answer)
B. Cutaneous fibromas
C. Cataract
D. Scoliosis

Explanation: **Explanation:** Neurofibromatosis (NF) refers to a group of genetic disorders, primarily NF1 (von Recklinghausen disease) and NF2 [3]. **1. Why Option A is the correct answer:** Neurofibromatosis (both NF1 and NF2) follows an **Autosomal Dominant** inheritance pattern, not autosomal recessive. NF1 is caused by a mutation in the *NF1* gene on chromosome 17, while NF2 is caused by a mutation in the *NF2* gene on chromosome 22. Approximately 50% of cases arise from *de novo* mutations, but they still exhibit dominant expression. **2. Analysis of incorrect options:** * **Cutaneous fibromas (B):** These are a hallmark feature of NF1 [2]. They appear as soft, non-tender, pedunculated skin tumors (neurofibromas) that typically develop during puberty. * **Cataract (C):** This is a specific diagnostic criterion for **NF2**. Patients often present with juvenile posterior subcapsular lenticular opacities (cataracts) at a young age. * **Scoliosis (D):** Skeletal dysplasias are common in NF1. Scoliosis is the most frequent skeletal manifestation, occurring in approximately 10–25% of affected individuals. **High-Yield Clinical Pearls for NEET-PG:** * **NF1 (Chromosome 17):** Characterized by Lisch nodules (iris hamartomas), Café-au-lait spots (≥6), axillary/inguinal freckling (Crowe sign), and Optic gliomas. * **NF2 (Chromosome 22):** Characterized by **Bilateral Acoustic Neuromas** (Vestibular Schwannomas), meningiomas, and cataracts [1]. * **Mnemonic:** NF**1** = Chromosome **17** (17 letters in Neurofibromatosis); NF**2** = Chromosome **22** (Everything comes in 2s: 2 ears, 2 eyes, 2 types of brain tumors). **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Manifestations Of Central And Peripheral Nervous System Disease, pp. 727-728. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1249-1250. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Peripheral Nerves and Skeletal Muscles, pp. 1248-1249.

Question 422: Which among the following is not an adhesion molecule?

A. Integrin
B. Selectin
C. Cadherins
D. Transferrin (Correct Answer)

Explanation: ### Explanation The correct answer is **Transferrin**. Cell Adhesion Molecules (CAMs) are specialized proteins located on the cell surface that facilitate cell-to-cell and cell-to-extracellular matrix (ECM) interactions [2]. These are crucial for processes like leukocyte extravasation, wound healing, and tissue architecture. **Why Transferrin is the correct answer:** Transferrin is a **plasma glycoprotein** synthesized in the liver [1]. Its primary function is the **transport of iron** in the blood [1][5]. It is not involved in cell adhesion or the docking of leukocytes to the endothelium. **Analysis of Incorrect Options:** * **Integrins (A):** These are transmembrane heterodimers that mediate **firm adhesion** of leukocytes to the endothelium by binding to ICAM-1 and VCAM-1 [3]. They also link the cytoskeleton to the ECM [3]. * **Selectins (B):** These molecules (L, E, and P-selectins) are responsible for the initial **rolling** phase of leukocyte recruitment [2]. They bind to sialylated oligosaccharides (like Sialyl-Lewis X) [4]. * **Cadherins (C):** These are calcium-dependent adhesion molecules that maintain intercellular junctions (e.g., E-cadherin in epithelial desmosomes). A loss of E-cadherin is a hallmark of **Epithelial-Mesenchymal Transition (EMT)** in cancer metastasis. **High-Yield Clinical Pearls for NEET-PG:** * **LAD Type 1:** Caused by a deficiency in **Integrins** (specifically CD18/β2 chain). * **LAD Type 2:** Caused by a deficiency in **Sialyl-Lewis X** (ligand for Selectins). * **PECAM-1 (CD31):** The molecule responsible for **diapedesis** (transmigration) through the endothelial intercellular junctions [4]. * **Selectins** mediate "Rolling"; **Integrins** mediate "Firm Adhesion" [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Red Blood Cell and Bleeding Disorders, pp. 657-658. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, p. 87. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 36-37. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Migration in the tissues toward a chemotactic stimulus, pp. 86-87. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 22-23.

Question 423: Which of the following is NOT an X-linked disorder?

A. Cystic fibrosis (Correct Answer)
B. Hemophilia A
C. Duchenne muscular dystrophy
D. Fragile X syndrome

Explanation: **Explanation:** The correct answer is **Cystic Fibrosis** because it is an **Autosomal Recessive (AR)** disorder, not an X-linked one. It is caused by a mutation in the **CFTR gene** located on the long arm of **Chromosome 7** [1]. This mutation leads to defective chloride ion transport [2], resulting in abnormally thick mucus secretions affecting the lungs, pancreas, and reproductive system [3]. **Analysis of other options:** * **Hemophilia A:** This is a classic **X-linked Recessive** bleeding disorder caused by a deficiency of Coagulation Factor VIII [4]. * **Duchenne Muscular Dystrophy (DMD):** This is an **X-linked Recessive** condition caused by a mutation in the *DMD* gene (the largest known human gene), leading to a complete absence of the dystrophin protein. * **Fragile X Syndrome:** This is an **X-linked Dominant** disorder (with variable expressivity) caused by a CGG trinucleotide repeat expansion in the *FMR1* gene [5]. It is the most common inherited cause of intellectual disability. **High-Yield Clinical Pearls for NEET-PG:** * **Cystic Fibrosis:** The most common lethal genetic disease in Caucasian populations. The most frequent mutation is **ΔF508** [1]. Diagnosis is confirmed via a **Sweat Chloride Test** (>60 mEq/L) [2]. * **X-linked Recessive Mnemonic:** "**G**o **H**ome **D**ear **F**riends, **C**olor **B**lindness **L**asts" (**G**6PD, **H**emophilia A/B, **D**MD/BMD, **F**abry disease, **C**hronic Granulomatous Disease, **B**ruton’s Agammaglobulinemia, **L**esch-Nyhan Syndrome). * Remember: X-linked recessive disorders typically affect males, while females are usually asymptomatic carriers [4]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, p. 476. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Lumen Of Sweat Duct, pp. 475-476. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 476-477. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, p. 151. [5] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 177-179.

Question 424: Which virus is known to cause hemopoietic carcinoma?

A. Epstein-Barr virus (EBV) (Correct Answer)
B. Human T-lymphotropic virus type I (HTLV-I)
C. Human herpesvirus 8 (HHV-8)
D. Cytomegalovirus (CMV)

Explanation: **Explanation:** The correct answer is **Epstein-Barr virus (EBV)**. EBV is a potent oncogenic DNA virus belonging to the Gammaherpesvirinae subfamily [3]. It primarily infects B-cells via the **CD21 (CR2) receptor** [1]. It is strongly associated with various hematopoietic malignancies (carcinomas of the lymphoid system), most notably **Burkitt Lymphoma** (starry-sky appearance), **Hodgkin Lymphoma** (mixed cellularity subtype), and **Post-transplant lymphoproliferative disorders (PTLD)** [3], [4]. Its oncogenic potential is driven by genes like **LMP-1**, which mimics CD40 signaling to promote B-cell proliferation and survival [4]. **Analysis of Incorrect Options:** * **HTLV-1:** While it causes **Adult T-cell Leukemia/Lymphoma (ATLL)**, it is an RNA retrovirus [3]. The question specifically points toward EBV as the classic prototype for hematopoietic oncogenesis in general pathology contexts. * **HHV-8:** Also known as Kaposi Sarcoma-associated Herpesvirus (KSHV). While it causes **Primary Effusion Lymphoma**, its primary association is with Kaposi Sarcoma (a vascular tumor), not broad hematopoietic carcinomas [2], [3]. * **CMV:** Although a member of the Herpesvirus family, CMV is not considered an oncogenic virus and is not associated with the development of hematopoietic malignancies. **High-Yield Clinical Pearls for NEET-PG:** * **EBV Associations:** Burkitt Lymphoma (t(8;14)), Nasopharyngeal Carcinoma, and Infectious Mononucleosis (atypical lymphocytes/Downey cells) [3]. * **Diagnosis:** Monospot test (heterophile antibodies) and EBV-specific serology (VCA, EBNA). * **Receptor:** EBV uses **gp350/220** to bind to **CD21** on B-cells [1]. * **Key Gene:** **LMP-1** prevents apoptosis by activating BCL-2 [4]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 368-369. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 261-262. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 219-220. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 335-336.

Question 425: What is the chance of having cystic fibrosis if only one parent is affected and the other is normal?

A. 25%
B. 50% (Correct Answer)
C. 70%
D. 80%

Explanation: **Explanation:** Cystic Fibrosis (CF) is an **Autosomal Recessive (AR)** disorder [1] caused by a mutation in the *CFTR* gene on chromosome 7. To understand the inheritance pattern in this specific question, we must apply the principles of Mendelian genetics. 1. **Why 50% is correct:** In the context of AR disorders like CF, an "affected" parent has the genotype **'aa'**. A "normal" parent in a population-based question is typically assumed to be a **carrier ('Aa')** unless specified as "genetically clear" or "homozygous normal." [1] * If the cross is **aa (Affected) × Aa (Carrier)**: The offspring probabilities are 50% affected (aa) and 50% carriers (Aa). * *Note:* If the other parent were homozygous normal (AA), the chance would be 0%. However, in medical entrance exams, if an affected person marries a "normal" person and a percentage is provided, it assumes the "Pseudodominance" pattern where the partner is a carrier. 2. **Why other options are incorrect:** * **25%:** This is the risk when **both** parents are asymptomatic carriers (Aa × Aa) [1]. * **70% & 80%:** These percentages do not correspond to standard Mendelian inheritance patterns for single-gene disorders. **NEET-PG High-Yield Pearls:** * **Pseudodominance:** When a recessive trait appears in every generation, mimicking a dominant pattern. This occurs when an affected individual (aa) mates with a carrier (Aa). * **Most Common Mutation:** ΔF508 (deletion of phenylalanine at position 508), leading to protein misfolding and degradation in the Golgi apparatus [2]. * **Diagnosis:** Sweat Chloride Test (>60 mEq/L) is the gold standard. * **Common Presentation:** Recurrent pulmonary infections (*P. aeruginosa*), pancreatic insufficiency, and meconium ileus in newborns. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 53-54. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, p. 476.

Question 426: What is the primary protein responsible for the tensile strength of tendons?

A. Fibrillin
B. Collagen (Correct Answer)
C. Fibronectin
D. Elastin

Explanation: **Explanation:** **1. Why Collagen is Correct:** Collagen is the most abundant protein in the human body and is the primary structural component of the extracellular matrix. Its unique triple-helical structure provides immense **tensile strength** (resistance to pulling forces) [1]. In **tendons**, which must transmit high mechanical loads from muscle to bone, **Type I Collagen** constitutes approximately 70-80% of the dry weight. These fibers are arranged in tight, parallel bundles to maximize their load-bearing capacity [1]. **2. Why Other Options are Incorrect:** * **Fibrillin (A):** This is a glycoprotein that forms a scaffold for elastin. It is essential for the structural integrity of connective tissue but does not provide the primary tensile strength. (Deficiency leads to Marfan Syndrome). * **Fibronectin (C):** This is an adhesive glycoprotein that helps cells attach to the extracellular matrix and plays a major role in cell migration and wound healing, rather than providing mechanical strength. * **Elastin (D):** As the name suggests, elastin provides **elasticity and recoil** to tissues (like the aorta, lungs, and skin), allowing them to return to their original shape after stretching. It lacks the tensile strength of collagen [1]. **3. NEET-PG High-Yield Pearls:** * **Type I Collagen:** Found in "Strong" tissues—**B**one, **S**kin, **T**endon, and late scars. (Mnemonic: **"1 is B-S-T"**). * **Type II Collagen:** Found in **C**artilage (Mnemonic: "Type **2** for **C**artilage"). * **Type III Collagen:** Found in blood vessels and early granulation tissue (Reticulin). * **Type IV Collagen:** Found in the **Basement Membrane** (Mnemonic: "Type **4** on the **Floor**"). * **Vitamin C** is a critical cofactor for the hydroxylation of proline and lysine residues during collagen synthesis; deficiency leads to Scurvy (poor wound healing and bleeding gums). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Genetic Disorders, pp. 154-155.

Question 427: HLA-I is present on which of the following?

A. All nucleated cells (Correct Answer)
B. Only on cells of the immune system
C. Only on B-cells
D. Only on T-cells

Explanation: ### Explanation **1. Why Option A is Correct:** Human Leukocyte Antigen (HLA) Class I molecules (HLA-A, B, and C) are fundamental components of the adaptive immune system. They are expressed on **all nucleated cells** [1], [2] and **platelets**. Their primary physiological role is to present endogenous antigens (such as viral proteins or tumor antigens) to **CD8+ Cytotoxic T-cells** [3]. Since any nucleated cell in the body is susceptible to viral infection or malignant transformation, they must all possess the machinery to signal the immune system for destruction. Note: Mature red blood cells (RBCs) lack HLA-I because they are non-nucleated. **2. Why Other Options are Incorrect:** * **Options B, C, and D:** These options are too restrictive. While cells of the immune system (including B-cells and T-cells) do express HLA-I, they are not the *only* cells to do so. These options describe the distribution pattern more characteristic of **HLA Class II** (HLA-DR, DP, DQ), which is restricted primarily to **Professional Antigen-Presenting Cells (APCs)** like dendritic cells, B lymphocytes, and macrophages [1]. **3. NEET-PG High-Yield Pearls:** * **Structure:** HLA-I consists of a polymorphic heavy chain (α-chain) and a non-polymorphic **β2-microglobulin** (encoded on Chromosome 15). * **Genetics:** The HLA gene complex is located on the **Short arm of Chromosome 6** [1]. * **Rule of 8:** HLA **I** x CD**8** = 8; HLA **II** x CD**4** = 8. * **Exceptions:** HLA-I is notably absent or expressed at very low levels on neurons, corneal endothelium, and villous trophoblasts (to prevent maternal immune rejection). * **Platelets:** Even though they lack a nucleus, platelets express HLA-I (inherited from megakaryocytes), which is clinically relevant in platelet transfusion refractoriness. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 156-157. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 200-201. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 240.

Question 428: Cell-mediated immune response is which type of hypersensitivity?

A. Type I
B. Type II
C. Type III
D. Type IV (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Type IV Hypersensitivity** Type IV hypersensitivity is also known as **Delayed-Type Hypersensitivity (DTH)** [1]. Unlike the other three types, it is **cell-mediated** rather than antibody-mediated [1]. It involves the activation of T-lymphocytes (specifically CD4+ Th1 cells and CD8+ cytotoxic T cells) [2]. Upon exposure to an antigen, sensitized T cells release cytokines (like IFN-gamma) that recruit macrophages or directly cause cellular cytotoxicity [1]. The reaction is "delayed" because it typically takes 48–72 hours to manifest [2]. **Why other options are incorrect:** * **Type I (Immediate):** Mediated by **IgE antibodies** and mast cell degranulation (e.g., Anaphylaxis, Asthma). * **Type II (Cytotoxic):** Mediated by **IgG or IgM antibodies** directed against antigens on specific cell surfaces or tissues (e.g., Autoimmune hemolytic anemia, Myasthenia gravis). * **Type III (Immune-Complex):** Mediated by the deposition of **antigen-antibody complexes** in tissues, leading to complement activation (e.g., SLE, Post-streptococcal glomerulonephritis). **High-Yield Clinical Pearls for NEET-PG:** * **Classic Examples of Type IV:** Mantoux (Tuberculin) test, Contact dermatitis (poison ivy, nickel), Graft rejection, and Granuloma formation (as seen in Tuberculosis or Leprosy) [3, 4]. * **Mnemonic (ACID):** * **A** - **A**naphylactic (Type I) * **C** - **C**ytotoxic (Type II) * **I** - **I**mmune Complex (Type III) * **D** - **D**elayed/Cell-mediated (Type IV) * **Key Cells:** The macrophage is the major effector cell in the delayed-type response, activated by T-cell-derived Interferon-gamma [1, 2]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 173-174. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 216-218. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 174-175. [4] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, p. 218.

Question 429: What is the most common type of ocular lymphoma?

A. T-cell lymphoma
B. Hodgkin's lymphoma
C. B-cell non-Hodgkin's lymphoma (Correct Answer)
D. Pre T-cell lymphoma

Explanation: **Explanation:** Primary Intraocular Lymphoma (PIOL) is a subset of Primary Central Nervous System Lymphoma (PCNSL). The vast majority (over 95%) of ocular lymphomas are **B-cell non-Hodgkin’s lymphomas**, specifically the **Diffuse Large B-cell Lymphoma (DLBCL)** subtype [1]. These typically involve the retina, vitreous, and optic nerve [1]. Another common site is the ocular adnexa (orbit, eyelids, conjunctiva), where **MALT lymphoma** (Extranodal Marginal Zone B-cell Lymphoma) is the most frequent histological type [2]. **Analysis of Options:** * **Option A & D (T-cell/Pre T-cell Lymphoma):** While T-cell lymphomas can occur in the eye, they are extremely rare [2]. They are more frequently associated with systemic involvement or specific geographic regions (e.g., NK/T-cell lymphoma in Asia). * **Option B (Hodgkin’s Lymphoma):** Hodgkin’s lymphoma almost exclusively involves the lymph nodes and very rarely presents as a primary extranodal disease in the eye. **Clinical Pearls for NEET-PG:** * **Masquerade Syndrome:** Ocular lymphoma is known as a "masquerade syndrome" because it often mimics chronic uveitis or vitritis, leading to delayed diagnosis [1]. * **CNS Association:** Approximately 60-80% of patients with primary vitreoretinal lymphoma will eventually develop CNS involvement [1]. * **Diagnostic Gold Standard:** Diagnostic vitrectomy with cytological examination and flow cytometry (looking for monoclonal B-cell populations) is the preferred investigation [1]. * **Cytokine Marker:** An elevated **IL-10 to IL-6 ratio (>1.0)** in the vitreous fluid is highly suggestive of B-cell lymphoma. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Eye, pp. 1341-1342. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Diseases Of The Urinary And Male Genital Tracts, pp. 565-566.

Question 430: A post-mortem clot is most likely to:

A. Grossly display features of recanalization
B. Grossly have lines of Zahn
C. Grossly have the appearance of “chicken fat” overlying “currant jelly” (Correct Answer)
D. Microscopically appear attached to the wall of the blood vessel

Explanation: ### Explanation The distinction between a **post-mortem clot** and a **thrombus** (pre-mortem) is a classic high-yield topic in pathology. **Why Option C is Correct:** Post-mortem clots occur after death when blood settles due to gravity (post-mortem hypostasis). Because the clotting process is slow and occurs in stagnant blood, red blood cells (RBCs) settle at the bottom due to gravity, while the lighter plasma and fibrin form a layer on top. This results in a characteristic **two-layered appearance**: * **"Currant jelly" (lower layer):** Dark red, dependent portion containing settled RBCs. * **"Chicken fat" (upper layer):** Yellowish, translucent portion consisting of fibrin and serum. **Why Other Options are Incorrect:** * **Option A & B:** Features like **recanalization** (formation of new capillary channels) and **Lines of Zahn** (alternating pale layers of platelets/fibrin and dark layers of RBCs) are hallmarks of **thrombi** formed in flowing blood. These require vital processes and blood flow, which are absent after death. * **Option D:** Post-mortem clots are **rubbery, gelatinous, and not attached** to the underlying vessel wall. In contrast, a true thrombus is typically firm, friable, and firmly adherent to the endothelium. ### NEET-PG High-Yield Pearls: * **Lines of Zahn:** Their presence is the definitive morphological evidence that a clot was formed in **flowing blood** (pre-mortem). They are most prominent in arterial or cardiac thrombi. * **Texture:** Post-mortem clots are "rubbery" and take the shape of the vessel (cast), whereas pre-mortem thrombi are "friable" (crumbly). * **Phlebothrombosis vs. Post-mortem Clot:** If a clot is found in a deep vein, look for attachment to the wall to diagnose Deep Vein Thrombosis (DVT) rather than post-mortem settling.

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