Fact-sheet: Hamartoma of lung
Updated on 11/04/2026 at 1:09 PM
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Definition
Benign mesenchymal tumor combining, in variable proportions, cartilage, fat, fibrous tissue, smooth muscle, and entrapped respiratory epithelium. Frequent cartilaginous predominance: chondromatous hamartoma. The concept of a simple malformation is outdated. [1,2]
- Most common benign pulmonary tumor; approximately 6% of solitary pulmonary nodules.
- Peripheral location in >90% of cases; endobronchial in approximately 5%.
- Usually solitary; slow growth.
Clinical features
Generally an incidental finding in an asymptomatic patient.
Endobronchial forms: cough, hemoptysis, bronchial obstruction; possible recurrent infections and downstream atelectasis. [3,5]
Laboratory findings
Possible inflammatory syndrome in the event of an infectious complication.
Radiography
- Round or oval nodule, well-defined, with smooth or lobulated margins; generally <4 cm.
- Coarse, “popcorn” calcifications, evocative when visible.
- Fat difficult to identify radiographically
- Endobronchial form: possible indirect signs of obstruction. [1,5]
CT
Gold standard examination: thin slices, ideally ≤ 1–1.5 mm, with parenchymal and mediastinal window analysis. [4,5]
- Morphology: peripheral, well-circumscribed, smooth or lobulated solid nodule, generally <4 cm.
- Macroscopic fat: approximately 60% of cases. Intranodular areas, typically between −40 and −120 HU; avoid partial volume averaging with peripheral air.
- "Popcorn" calcifications: 20–30% of cases. Possible more discreet or punctate calcifications.
- Characteristic fat–calcification association: very high diagnostic value.
- Post-contrast: variable enhancement, particularly peripheral or septal; sometimes diffuse and non-specific.
- Endobronchial form: intraluminal nodule, with investigation for downstream atelectasis, air trapping, or infection. [1,5]
- The absence of fat or calcification does not exclude a hamartoma, but often prevents its formal characterization.
In atypical forms, Habert et al. report that a median volume attenuation <10 HU on contrast-enhanced CT favors hamartoma: 100% specificity, 23% sensitivity in their external cohort. Ancillary criterion, method-dependent; do not confuse it with a macroscopic fat threshold. [3]
MRI
Second-line examination; rarely necessary after a characteristic CT scan.
- T1-weighted images: intermediate and heterogeneous signal; high-signal fatty foci, suppressed on fat-saturated sequences.
- T2-weighted images: high-signal of the cartilaginous component; low-signal of the fibrous or calcified elements.
- After gadolinium: heterogeneous enhancement, often septal or peripheral.
- No isolated MRI criterion allows for the confirmation of all fat-poor forms. [5]
Vascular intervention
CT-guided transthoracic biopsy: to be considered for an indeterminate nodule if the result changes patient management; unnecessary in the presence of typical features.
Nuclear medicine
¹⁸F-FDG PET-CT: generally low uptake, but hypermetabolism/increased uptake is possible; non-specific result.
No indication in the presence of a typical hamartoma on CT. In an indeterminate nodule, PET contributes to the overall risk assessment without establishing the diagnosis on its own. [3,4]
Management
- Typical appearance, asymptomatic: therapeutic abstention; comparison with previous examinations.
- Follow-up: The 2017 Fleischner recommendations exempt clearly benign-appearing nodules from follow-up, notably fatty and calcified ones. Adapt monitoring to diagnostic certainty, without automatically applying the schedule for indeterminate nodules. [4]
- Indeterminate appearance: management according to size, morphology, progression, and clinical risk; CT follow-up, PET-CT, or biopsy depending on the context.
- Endobronchial form: bronchoscopic exploration and sampling; endoscopic resection possible if obstruction.
- Suspicious growth, symptoms, obstructive complication, or persistent doubt: multidisciplinary discussion; endoscopic resection or parenchyma-sparing surgical resection. [4,5]
The Fleischner guidelines apply to incidental nodules in adults ≥35 years of age, excluding screening, known cancer, and immunosuppression. [4]
Differential diagnosis
- Pulmonary carcinoid: Main pitfall of fat-poor forms; enhancement is often marked, bronchial relationship, and obstructive signs. Calcifications may be present.
- Bronchopulmonary cancer or pulmonary metastasis: To consider for any indeterminate nodule; spiculation, growth, oncological history. An isolated calcification does not exclude malignancy.
- Calcified granuloma: Central, diffuse, or laminated calcifications; absence of intranodular fat.
- Pulmonary chondroma: Often larger, heavily calcified, without macroscopic fat. Possible association with Carney's triad = pulmonary chondroma + gastric GIST + extra-adrenal paraganglioma.
- Endobronchial lipoma : Essentially fatty and homogeneous lesion, responsible for bronchial obstruction.
Do not equate pulmonary hamartoma with chondroma of Carney triad. [1,3,5]
References
- Toussie D, et al. Pulmonary Calcification and Ossification: Pathogenesis, CT Appearance, and Specific Disorders. RadioGraphics. 2025;45(6):e240110. DOI: 10.1148/rg.240110.
- Lee MH, et al. Multimodality Imaging of Hamartomas: Interactive Case-based Approach. RadioGraphics. 2023;43(4):e220127. DOI: 10.1148/rg.220127.
- Habert P, et al. Best imaging signs identified by radiomics could outperform the model: application to differentiating lung carcinoid tumors from atypical hamartomas. Insights Imaging. 2023;14:148. DOI: 10.1186/s13244-023-01484-9.
- MacMahon H, et al. Guidelines for Management of Incidental Pulmonary Nodules Detected on CT Images: From the Fleischner Society 2017. Radiology. 2017;284:228–243. DOI: 10.1148/radiol.2017161659.
- WHO Classification of Tumours Editorial Board. Thoracic Tumours. 5th ed., vol. 5. Lyon: IARC; 2021.
