A biopsy from a lung lesion shows the histological features depicted in the image. The most likely diagnosis is:

Explanation

## Image Findings * Extensive deposition of large, amorphous, acellular, eosinophilic (pink), hyaline material in the extracellular space. * Prominent chronic inflammatory infiltrate, primarily lymphocytes and plasma cells, surrounding the eosinophilic deposits. * Presence of multinucleated giant cells (foreign body type) adjacent to the deposited material. * The deposits appear somewhat nodular and confluent within the tissue. ## Diagnosis **Key Point:** The image shows characteristic amorphous, eosinophilic, hyaline extracellular deposits with surrounding chronic inflammation and giant cells, pathognomonic for amyloidosis. The image demonstrates large, irregular deposits of **amorphous, eosinophilic, hyaline material** in the tissue, which is the hallmark of **amyloid**. These deposits are extracellular and appear somewhat nodular. They are surrounded by a **chronic inflammatory infiltrate** composed mainly of lymphocytes and plasma cells. The presence of **multinucleated giant cells** further supports a chronic reactive process around the deposited material. This combination of findings, particularly the nature of the extracellular deposits, is highly characteristic of **amyloidosis**, and given the context of a lung lesion and the nodular appearance, **pulmonary nodular amyloidosis** is the most fitting diagnosis. Special stains like Congo Red (showing apple-green birefringence under polarized light) would confirm amyloid. ## Differential Diagnosis | Feature | Pulmonary Nodular Amyloidosis | Tuberculosis (Caseating Granuloma) | Pulmonary Alveolar Proteinosis | | :---------------------- | :---------------------------------------------------------- | :---------------------------------------------------------------- | :-------------------------------------------------------------- | | **Key Histology** | Amorphous, eosinophilic, hyaline extracellular deposits; chronic inflammation; giant cells. | Granulomas with central caseous necrosis; epithelioid histiocytes; Langhans giant cells; lymphocytes. | Alveoli filled with granular, eosinophilic, proteinaceous material (surfactant); minimal inflammation. | | **Nature of Deposits** | Protein fibrils (amyloid) | Necrotic cellular debris, lipid | Surfactant lipoprotein | | **Special Stains** | Congo Red (apple-green birefringence) | Ziehl-Neelsen (AFB stain for mycobacteria) | PAS positive, diastase resistant | ## Clinical Relevance **Clinical Pearl:** Pulmonary nodular amyloidosis often presents as solitary or multiple well-circumscribed nodules on imaging, mimicking malignancy. It is typically a localized form of amyloidosis and has a good prognosis, unlike systemic amyloidosis. ## High-Yield for NEET PG **High-Yield:** Amyloid is characterized by **amorphous, eosinophilic, hyaline extracellular deposits** that show **apple-green birefringence** under polarized light after **Congo Red staining**. **Key Point:** The most common type of amyloidosis affecting the lung is **AL (light chain) amyloidosis**, which can be localized or part of systemic disease. Nodular amyloidosis is usually localized. ## Common Traps **Warning:** Do not confuse the homogeneous eosinophilic deposits of amyloid with caseous necrosis (which is granular and often surrounded by well-formed granulomas) or hyaline membranes (which line alveolar spaces). The amorphous, homogeneous, and extracellular nature of amyloid is key. ## Reference [cite:Robbins Basic Pathology, 10th Ed, Ch 5, Ch 15]