Case 2- Pulmonary Hamartoma

Case 2 - 43 years old lady with severe dengue. Incidental finding during postmortem: Right upper lobe lung nodule.

Histopathology of pulmonary hamartoma:
 * Gross appearance: Pulmonary hamartomas are typically well-circumscribed, solitary nodules that can range in size from a few millimeters to several centimeters (Most are less than 40 mm) . They often have a firm, rubbery texture and may have a gritty or calcified feel due to the presence of cartilage.
 * Microscopic appearance: Histologically, pulmonary hamartomas are characterized by a haphazard arrangement of mature mesenchymal elements, such as cartilage, fat, bland myxoid spindle cells, smooth muscle,  fibrous connective tissue and bone, interspersed with islands of respiratory epithelium. The cartilage is often hyaline or fibrocartilaginous and may show calcification or ossification. The fat cells are mature adipocytes. The smooth muscle cells are arranged in bundles or sheets. The respiratory epithelium is typically normal and may line cysts or alveolar spaces.
Key features for diagnosis:
 * Presence of at least two different benign mesenchymal elements (e.g., cartilage and fat, cartilage and smooth muscle, or fat and myxoid spindle cells)
 * Entrapment of respiratory epithelium within the mesenchymal elements
Additional notes:
 * Pulmonary hamartomas are usually benign and do not require treatment unless they are causing symptoms or are large enough to be mistaken for a malignancy.
 * In rare cases, pulmonary hamartomas may be associated with other conditions, such as Carney triad, which is a syndrome that includes pulmonary hamartoma, functioning extra-adrenal paragangliomas, and gastrointestinal stromal tumors.

Differential diagnosis :
* Monomorphic soft tissue tumours - Presence of more than one mesenchymal  component in pulmonary hamartoma.
* Pulmonary chondromas - Typically arise in patients with Carney triad and lack entrapped epithelium. SDHB immmunohistochemistry may be useful; it shows abnormal loss in Carney-associated chondroma , but not in pulmonary hamartoma.
* Endobronchial lipoma Vs lipomatous hamartoma, whereas epithelial inclusions tend to be inconspicuous- Distinction is generally not critical.
* If only myxoid spindle cell component is sampled  - which could lead to consideration of myxoid periheral nerve sheath tumour or even myxoid sarcoma - Unlike those of sarcomas, the spindle cells of hamartoma are generally very bland, without atypia, and they have very low cellularity.  

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