Respiratory Pathology — MCQs

A radiographic study of inhalational lung diseases is conducted. One pattern of involvement is seen in persons whose total lung capacity, diffusing capacity, and compliance are decreased. This pattern consists of numerous bilateral nodular opacifications on chest radiographs. Polarizable needlelike crystals are seen on microscopic examination of these nodules. What inhaled substance is most likely to produce these findings?

Q178Easy

What are the characteristic features of Pneumocystis jirovecii pneumonia (PCP)?

Q179Hard

A 45-year-old man has had progressive dyspnea on exertion with fatigue for the past 2 years. On auscultation of his chest, he has a prominent pulmonary component of S2, a systolic murmur of tricuspid insufficiency, and bruits over peripheral lung fields. Jugular venous distension is present to the angle of his jaw when sitting. Laboratory studies show antiphospholipid antibodies. CT angiography shows eccentric occlusions in the pulmonary arteries and mosaic attenuation of pulmonary parenchyma. Which of the following is the most likely disease process causing his pulmonary disease?

Q180Medium

A patient presents with recurrent episodic diarrhea, triggered by food or alcohol. During episodes, he experiences flushing, wheezing, and malaise. A chest x-ray reveals a lung mass. Which of the following would MOST likely be present on biopsy of the lesion?

Respiratory Pathology Indian Medical PG Practice Questions and MCQs

Question 171: What is a newer inclusion in the 2015 WHO classification of squamous cell carcinoma of lung?

A. Clear cell variant
B. Papillary cell variant
C. Adenocarcinoma variant
D. Nonkeratinizing variant (Correct Answer)

Explanation: ### Explanation The **2015 WHO Classification of Lung Tumors** introduced significant changes to the subtyping of Squamous Cell Carcinoma (SCC) to improve diagnostic reproducibility and align with molecular pathology. **Why the correct answer is right:** In the 2015 update, the classification of Squamous Cell Carcinoma was simplified into three main variants: 1. **Keratinizing SCC:** Shows obvious keratinization (pearls/individual cell keratinization). 2. **Non-keratinizing SCC:** Shows squamous differentiation (intercellular bridges) but lacks overt keratinization. This is the **newer inclusion** and is diagnosed when the tumor is solid but expresses squamous markers (p40, p63, CK5/6). 3. **Basaloid SCC:** A variant where the basaloid component exceeds 50%. **Why the other options are wrong:** * **Clear cell and Papillary variants (Options A & B):** These were recognized in the older 2004 WHO classification but were **deleted** in 2015. They are now considered "morphological features" rather than distinct subtypes because they lacked clinical or prognostic significance. * **Adenocarcinoma variant (Option C):** This is not a variant of SCC. If a tumor shows both squamous and glandular differentiation, it is classified as **Adenosquamous Carcinoma** [1]. **High-Yield NEET-PG Pearls:** * **Most common site:** SCC is typically **central/hilar** in location and strongly associated with **smoking** [1]. * **IHC Markers:** The most specific marker for SCC is **p40** (superior to p63). It is also positive for **CK5/6**. * **Paraneoplastic Syndrome:** SCC is most commonly associated with **Hypercalcemia** due to the secretion of Parathyroid Hormone-related Protein (PTHrP). * **Cavitation:** Among lung cancers, SCC is the most likely to undergo central necrosis and **cavitation**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 721-723.

Question 172: Which of the following types of emphysema is most commonly associated with chronic smoking?

A. Centriacinar emphysema (Correct Answer)
B. Panacinar emphysema
C. Irregular emphysema
D. Mixed variety emphysema

Explanation: **Explanation:** **1. Why Centriacinar Emphysema is Correct:** Centriacinar (centrilobular) emphysema is the most common form of emphysema and is characteristically associated with **chronic cigarette smoking** in individuals without alpha-1 antitrypsin deficiency [1], [2]. In this type, the central or proximal parts of the acini (formed by respiratory bronchioles) are affected, while distal alveoli are spared [1]. This pattern occurs because inhaled cigarette smoke particles preferentially settle in the small airways, triggering an inflammatory response and protease release that destroys the walls of the respiratory bronchioles. It is typically more severe in the **upper lobes** of the lungs [3]. **2. Why Other Options are Incorrect:** * **Panacinar Emphysema:** This involves uniform destruction of the entire acinus (from respiratory bronchiole to terminal alveoli) [3]. It is classically associated with **Alpha-1 Antitrypsin (A1AT) deficiency** and tends to involve the **lower lobes** more severely [1]. * **Irregular Emphysema:** This is associated with **scarring** (paracicatricial) [3]. The acinus is irregularly involved, and it is usually asymptomatic and found incidentally [1]. * **Mixed Variety:** While patients with advanced COPD may show a combination of patterns, "Mixed" is not the primary pathological classification linked to smoking [2]. **3. NEET-PG High-Yield Pearls:** * **Location:** Centriacinar = Upper Lobes (Smoking); Panacinar = Lower Lobes (A1AT deficiency). * **Distal Acinar (Paraseptal) Emphysema:** Often seen near the pleura; it is the most common cause of **spontaneous pneumothorax** in young adults [3]. * **Protease-Antiprotease Hypothesis:** The fundamental mechanism of emphysema is an imbalance where excess proteases (like elastase) destroy lung tissue because of insufficient neutralizing antiproteases [1]. * **Microscopy:** Look for "floating" septa (alveolar walls that end abruptly in the alveolar space). **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 684-685. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 326-327. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 683.

Question 173: Thickening of the pulmonary alveolar-capillary membrane is seen in which of the following conditions?

A. Asthma
B. Bronchitis
C. Pulmonary fibrosis (Correct Answer)
D. Emphysema

Explanation: **Explanation:** The **alveolar-capillary membrane** (blood-air barrier) is the structure through which gas exchange occurs. It consists of the alveolar epithelium, the fused basement membrane, and the capillary endothelium. **Why Pulmonary Fibrosis is correct:** Pulmonary fibrosis is the hallmark of **Interstitial Lung Diseases (ILD)**. It involves chronic inflammation and the excessive deposition of collagen and extracellular matrix within the alveolar walls (interstitium) [1]. This pathologically **thickens the membrane**, increasing the diffusion distance for oxygen and carbon dioxide, leading to a "diffusion defect" and restrictive lung disease [1]. **Why the other options are incorrect:** * **Asthma:** A chronic inflammatory airway disease characterized by reversible bronchoconstriction and hypertrophy of bronchial smooth muscle. It affects the **conducting airways**, not the alveolar-capillary membrane. * **Bronchitis:** Specifically chronic bronchitis involves mucus gland hyperplasia and inflammation of the **bronchi**. While it causes airway obstruction, it does not primarily thicken the gas-exchange membrane. * **Emphysema:** Characterized by the **destruction** of alveolar walls and permanent enlargement of airspaces. Rather than thickening the membrane, it results in a loss of surface area for gas exchange. **High-Yield Clinical Pearls for NEET-PG:** * **Diffusion Capacity (DLCO):** In pulmonary fibrosis, DLCO is **decreased** due to the increased thickness of the membrane. * **Radiology:** Look for "Honeycombing" and "Ground-glass opacities" on HRCT, which are classic signs of advanced fibrosis [1]. * **Spirometry:** Pulmonary fibrosis shows a **Restrictive pattern** (Decreased FVC, Normal or Increased FEV1/FVC ratio) [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 691-695.

Question 174: All are true about silicosis except?

A. Bifringent crystals are seen
B. Pleural plaque is seen
C. The lower lobe is usually involved (Correct Answer)
D. It is the most common pneumoconiosis

Explanation: Silicosis is a chronic fibrotic lung disease caused by the inhalation of crystalline silicon dioxide [1]. **Why Option C is the correct answer (False statement):** Unlike asbestosis, which primarily affects the lower lobes [1], **silicosis predominantly involves the upper lobes** of the lungs [1]. The inhaled silica particles are ingested by alveolar macrophages, which then release inflammatory cytokines, leading to the formation of characteristic silicotic nodules in the upper zones and hilar lymph nodes. **Analysis of other options:** * **Option A (Birefringent crystals):** Under polarized light, silica particles appear as weakly birefringent (doubly refractive) crystals. This is a classic histopathological finding. * **Option B (Pleural plaques):** While more characteristic of asbestosis [1], pleural plaques can occasionally be seen in silicosis. However, the more classic pleural finding in silicosis is pleural thickening or adhesions. * **Option D (Most common pneumoconiosis):** Silicosis is globally recognized as the most common chronic occupational lung disease [1], particularly in industries like mining, sandblasting, and stone cutting [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Eggshell Calcification:** A pathognomonic radiological finding where hilar lymph nodes show peripheral calcification. * **TB Association:** Silicosis patients have a **3-fold increased risk** of developing Tuberculosis (Silicotuberculosis) because silica impairs macrophage function [1]. * **PMF:** Progression can lead to Progressive Massive Fibrosis (PMF), where nodules coalesce into large scars [1]. * **Caplan Syndrome:** The association of silicosis (or coal worker's pneumoconiosis) with Rheumatoid Arthritis [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 695-699.

Question 175: A 70-year-old man, with a 10-15 year history of working in an asbestos factory, has a mass detected in the right apical region of his lung on a routine X-ray. A biopsy was taken from the mass. What is seen on electron microscopic examination of the biopsy?

A. Numerous long, slender microvilli (Correct Answer)
B. Neurosecretory granules in the cytoplasm
C. Melanosomes
D. Desmosomes

Explanation: ### Explanation The patient’s history of long-term asbestos exposure and the presence of a lung mass strongly suggest a diagnosis of **Malignant Mesothelioma** [2]. While asbestos exposure also increases the risk of bronchogenic carcinoma [1], the classic association tested in pathology regarding asbestos and specific ultrastructural findings is mesothelioma. **1. Why Option A is Correct:** On **Electron Microscopy (EM)**, the hallmark of malignant mesothelioma is the presence of **numerous, long, slender, and bushy microvilli** on the cell surface. These microvilli typically have a high length-to-diameter ratio (often >10:1). In contrast, adenocarcinoma of the lung presents with short, blunt, and sparse microvilli. This distinction is a classic "gold standard" for differentiating these two tumors under EM. **2. Why the Other Options are Incorrect:** * **B. Neurosecretory granules:** These are characteristic of neuroendocrine tumors, such as **Small Cell Carcinoma** or Carcinoid tumors. * **C. Melanosomes:** These are the ultrastructural hallmark of **Melanoma**. * **D. Desmosomes:** While present in many epithelial tumors, prominent well-developed desmosomes associated with tonofilaments are characteristic of **Squamous Cell Carcinoma**. **Clinical Pearls for NEET-PG:** * **Most Common Cancer in Asbestos Exposure:** Bronchogenic Carcinoma (though Mesothelioma is the most *specific*) [1]. * **Latent Period:** Mesothelioma has a long latency period (25–40 years) [4]. * **Immunohistochemistry (IHC):** Mesothelioma is typically **Calretinin (+)**, WT-1 (+), and Cytokeratin 5/6 (+), but **CEA (-)** [2]. * **Asbestos Bodies:** Also known as Ferruginous bodies (golden-brown, fusiform/beaded rods with an iron-protein coat) [3]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 699. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 731. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 698-699. [4] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 339-340.

Question 176: Which type of lung malignancy is known to produce ACTH-like substances?

A. Squamous cell carcinoma
B. Small cell lung carcinoma (Correct Answer)
C. Large cell carcinoma
D. Oat cell carcinoma

Explanation: **Explanation:** **Small cell lung carcinoma (SCLC)**, also known as **Oat cell carcinoma** [1], is a highly aggressive neuroendocrine tumor. Because it originates from neuroendocrine (Kulchitsky) cells, it has the metabolic machinery to synthesize and secrete various polypeptide hormones. This leads to **Paraneoplastic Syndromes** [2], the most classic being the ectopic production of **ACTH (Adrenocorticotropic Hormone)**, which results in Cushing syndrome, and **ADH (Antidiuretic Hormone)**, which results in SIADH. **Analysis of Options:** * **Small cell lung carcinoma (Option B):** This is the correct answer. It is the most common lung cancer associated with ectopic ACTH production. * **Oat cell carcinoma (Option D):** While "Oat cell" is a histological subtype/synonym for Small cell carcinoma [1], in the context of standard medical examinations, if both are provided, the broader clinical term (SCLC) is typically preferred unless the question specifically asks for histological morphology. (Note: In many exams, these are considered synonymous; however, SCLC is the standard clinical classification). * **Squamous cell carcinoma (Option A):** This is characteristically associated with the production of **PTHrP** (Parathyroid Hormone-related Protein), leading to hypercalcemia. It is not typically associated with ACTH. * **Large cell carcinoma (Option C):** This is a diagnosis of exclusion and is more commonly associated with the production of **Beta-hCG**, leading to gynecomastia. **High-Yield Clinical Pearls for NEET-PG:** * **SCLC Associations:** ACTH (Cushing), ADH (SIADH), and Lambert-Eaton Myasthenic Syndrome (antibodies against voltage-gated calcium channels) [2]. * **Squamous Cell (SCC) Associations:** "P" rule — **P**THrP, **P**earl formation (keratin), **P**rimal (central) location, and **P**resent in smokers. * **Adenocarcinoma:** Most common type in non-smokers and females; associated with hypertrophic osteoarthropathy (clubbing). **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 337-338. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 725-727.

Question 177: A radiographic study of inhalational lung diseases is conducted. One pattern of involvement is seen in persons whose total lung capacity, diffusing capacity, and compliance are decreased. This pattern consists of numerous bilateral nodular opacifications on chest radiographs. Polarizable needlelike crystals are seen on microscopic examination of these nodules. What inhaled substance is most likely to produce these findings?

A. Cigarette smoke
B. Mold spores
C. Silica dust (Correct Answer)
D. Sulfur dioxide

Explanation: ### Explanation The clinical presentation describes **Silicosis**, the most common chronic occupational lung disease worldwide [1]. **Why Silica dust is correct:** * **Restrictive Lung Disease:** The decrease in total lung capacity (TLC), diffusing capacity (DLCO), and compliance indicates a restrictive pattern caused by progressive pulmonary fibrosis [1]. * **Radiographic Findings:** Silicosis typically presents with numerous small, rounded, bilateral nodular opacities, predominantly in the upper lobes [1]. * **Microscopic Hallmark:** The pathognomonic finding is the **silicotic nodule**, characterized by concentric layers of hyalized collagen. Under polarized light, these nodules contain **birefringent (polarizable) needle-like silica particles** [1]. **Why the other options are incorrect:** * **Cigarette smoke:** Primarily associated with COPD (obstructive pattern) and bronchogenic carcinoma. It does not produce polarizable crystalline nodules. * **Mold spores:** Associated with Hypersensitivity Pneumonitis (e.g., Farmer’s lung) [2]. While it causes a restrictive pattern, the histology shows poorly formed non-caseating granulomas, not polarizable crystals. * **Sulfur dioxide:** A soluble gas that causes acute mucosal irritation, bronchospasm, or chemical pneumonitis, but not chronic nodular fibrosis. **High-Yield NEET-PG Pearls:** * **Eggshell Calcification:** Hilar lymph nodes in silicosis may show peripheral calcification known as "eggshell calcification." * **TB Association:** Silicosis increases susceptibility to **Tuberculosis** (Silicotuberculosis) because silica impairs macrophage function (phagolysosome formation) [1]. * **Occupations:** Look for histories involving sandblasting, stone cutting, mining, or ceramics [2]. * **Caplan Syndrome:** The coexistence of silicosis (or coal worker's pneumoconiosis) and Rheumatoid Arthritis [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 697-698. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, p. 695.

Question 178: What are the characteristic features of Pneumocystis jirovecii pneumonia (PCP)?

A. Interstitial pneumonitis
B. Eosinophilic exudate
C. Damage to Type I pneumocytes
D. All of the above (Correct Answer)

Explanation: **Explanation:** *Pneumocystis jirovecii* is an opportunistic fungal pathogen that primarily affects immunocompromised individuals [1], particularly those with HIV/AIDS (CD4 count <200 cells/µL). The pathogenesis and histopathology of PCP are high-yield topics for NEET-PG. 1. **Damage to Type I Pneumocytes:** The organism attaches specifically to Type I pneumocytes. This attachment causes direct cellular injury, leading to increased alveolar-capillary permeability and impaired gas exchange. 2. **Eosinophilic Exudate:** As a result of the injury, a characteristic "cotton-candy" or "honeycomb" intra-alveolar exudate accumulates [1]. This is a proteinaceous, eosinophilic material that contains the proliferating organisms and cellular debris. 3. **Interstitial Pneumonitis:** While the exudate is intra-alveolar, the underlying host response involves the thickening of the alveolar septa with mononuclear infiltrates (plasma cells and lymphocytes), leading to an interstitial pattern on imaging. **Why "All of the above" is correct:** The disease process is a triad of direct cellular damage (Type I pneumocytes), the resulting inflammatory response in the septa (interstitial pneumonitis), and the accumulation of the characteristic fluid (eosinophilic exudate). **High-Yield Clinical Pearls for NEET-PG:** * **Stains:** Silver stains (Grocott-Gomori Methenamine Silver - **GMS**) are the gold standard to visualize the crushed-cup or boat-shaped cysts [1]. **PAS stain** also highlights the cysts. * **Radiology:** Classically presents as bilateral, perihilar "ground-glass opacities" (GGO). * **Diagnosis:** Bronchoalveolar lavage (BAL) is the preferred diagnostic procedure. * **Treatment:** Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice for both treatment and prophylaxis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 318-319.

Question 179: A 45-year-old man has had progressive dyspnea on exertion with fatigue for the past 2 years. On auscultation of his chest, he has a prominent pulmonary component of S2, a systolic murmur of tricuspid insufficiency, and bruits over peripheral lung fields. Jugular venous distension is present to the angle of his jaw when sitting. Laboratory studies show antiphospholipid antibodies. CT angiography shows eccentric occlusions in the pulmonary arteries and mosaic attenuation of pulmonary parenchyma. Which of the following is the most likely disease process causing his pulmonary disease?

A. Atherosclerosis
B. Pneumonitis
C. Sarcoidosis
D. Thromboembolism (Correct Answer)

Explanation: **Explanation:** The clinical presentation describes **Chronic Thromboembolic Pulmonary Hypertension (CTEPH)**. The key to this diagnosis lies in the combination of chronic progressive dyspnea, signs of right heart failure (prominent P2, tricuspid regurgitation, JVD), and specific imaging findings [1]. 1. **Why Thromboembolism is correct:** The patient has **Antiphospholipid Syndrome (APS)**, a hypercoagulable state that predisposes to recurrent venous thromboembolism. In CTEPH, organized thrombi attach to the arterial walls, leading to **eccentric occlusions** (as seen on CT) and narrowing of the pulmonary vascular bed [1]. This causes **mosaic attenuation** on CT (areas of hyperperfusion vs. hypoperfusion) and **bruits** over the lung fields due to turbulent flow through partially obstructed vessels. Chronic accumulation of damage from many tiny embolic events leads to pulmonary hypertension and chronic cor pulmonale [2]. 2. **Why other options are incorrect:** * **Atherosclerosis:** While pulmonary atherosclerosis can occur secondary to long-standing pulmonary hypertension, it is a pathological consequence, not the primary cause of the eccentric occlusions and mosaicism described [1]. * **Pneumonitis:** This typically presents with fever, cough, and infiltrates on imaging, rather than signs of chronic pulmonary vascular obstruction and right heart failure. * **Sarcoidosis:** While it can cause pulmonary hypertension, it typically presents with hilar lymphadenopathy and restrictive lung patterns, not eccentric arterial occlusions or bruits. **High-Yield Pearls for NEET-PG:** * **CTEPH (WHO Group 4):** It is the only form of pulmonary hypertension that is potentially curable (via pulmonary endarterectomy). * **Mosaic Attenuation:** A classic CT sign of regional differences in lung perfusion, highly suggestive of chronic thromboembolic disease [1]. * **APS Association:** Always screen for Antiphospholipid antibodies in young/middle-aged patients with unexplained pulmonary hypertension or recurrent clots [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 705-707. [2] 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. 144-145.

Question 180: A patient presents with recurrent episodic diarrhea, triggered by food or alcohol. During episodes, he experiences flushing, wheezing, and malaise. A chest x-ray reveals a lung mass. Which of the following would MOST likely be present on biopsy of the lesion?

A. Bronchioloalveolar carcinoma
B. Carcinoid tumor (Correct Answer)
C. Primary tuberculosis
D. Recurrent tuberculosis

Explanation: ### Explanation **Correct Answer: B. Carcinoid tumor** **1. Why it is correct:** The patient presents with the classic triad of **Carcinoid Syndrome**: flushing, wheezing (bronchoconstriction), and diarrhea. This syndrome occurs when a neuroendocrine tumor secretes vasoactive substances, primarily **Serotonin (5-HT)**, into the systemic circulation [1]. While most carcinoid tumors arise in the GI tract (where symptoms only occur after liver metastasis), **Bronchial Carcinoids** can secrete serotonin directly into the systemic circulation via the pulmonary veins, bypassing hepatic metabolism [1]. This explains the presence of systemic symptoms alongside a lung mass. **2. Why the other options are incorrect:** * **A. Bronchioloalveolar carcinoma (now Adenocarcinoma in situ):** Typically presents as a peripheral solitary nodule or "pneumonia-like" consolidation [2]. It does not produce neuroendocrine hormones and would not cause flushing or diarrhea. * **C & D. Primary/Recurrent Tuberculosis:** While TB can cause a lung mass (tuberculoma) and constitutional symptoms like malaise, it presents with fever, night sweats, and hemoptysis. It does not cause the episodic vasomotor symptoms (flushing) or wheezing characteristic of carcinoid syndrome. **3. High-Yield NEET-PG Pearls:** * **Origin:** Derived from **Kulchitsky cells** (enterochromaffin cells) of the bronchial epithelium. * **Histology:** Characterized by "Organoid" patterns—nests, cords, or trabeculae of uniform cells with **"Salt and Pepper" chromatin** [1]. * **Markers:** Positive for **Chromogranin A**, **Synaptophysin**, and CD56; by immunohistochemistry, they are found to contain serotonin [1]. * **Diagnosis:** Elevated **24-hour urinary 5-HIAA** (a metabolite of serotonin). * **Location:** Bronchial carcinoids are often central/intraluminal, leading to persistent cough, hemoptysis, or obstructive pneumonia [1]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lung, pp. 725-727. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 336-337.

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