Definition/General
Introduction:
Pulmonary hamartoma is the most common benign lung tumor
Represents 6-8% of all pulmonary nodules
Composed of disorganized mature tissues
Shows cartilage, fat, and connective tissue
Excellent prognosis.
Origin:
Developmental malformation of mesenchymal tissues
Contains normal lung components in abnormal arrangement
Clonal neoplasm rather than true hamartoma
Shows chromosomal rearrangements.
Classification:
Location: Endobronchial hamartoma (10%)
Parenchymal hamartoma (90%)
Composition: Chondroid type (most common)
Lipomatous type
Mixed type.
Epidemiology:
Peak incidence 5th-6th decades
Male predominance (3:1)
No smoking association
Usually solitary
Multiple hamartomas in Cowden syndrome.
Clinical Features
Presentation:
Asymptomatic (90%)
Incidental finding
Cough (endobronchial)
Hemoptysis
Post-obstructive pneumonia
Chest pain rare.
Symptoms:
Usually asymptomatic
Chronic cough (endobronchial type)
Sputum production
Shortness of breath
Recurrent pneumonia
Wheeze.
Risk Factors:
No specific risk factors
Cowden syndrome (multiple hamartomas)
PTEN mutations
Family history (rare)
No environmental factors.
Screening:
Chest X-ray
CT scan: fat and calcification
Popcorn calcification
Bronchoscopy (endobronchial)
PET scan: no uptake.
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Gross Description
Appearance:
Well-circumscribed nodule
Lobulated surface
Gray-white to yellow
Firm consistency
Glistening cartilage
Fatty areas.
Characteristics:
Smooth, lobulated
Encapsulated
Variegated cut surface
Cartilaginous areas
Adipose tissue
Fibrous septa.
Size Location:
Peripheral location (90%)
Lower lobe predilection
Variable size (0.5-10 cm)
Slow growth
Endobronchial (central airways).
Multifocality:
Usually solitary
Multiple hamartomas (Cowden syndrome)
Bilateral lesions rare
No malignant transformation.
Microscopic Description
Histological Features:
Mature hyaline cartilage
Mature adipose tissue
Fibrous connective tissue
Smooth muscle
Respiratory epithelium
Calcification.
Cellular Characteristics:
Mature chondrocytes
Adipocytes
Fibroblasts
Smooth muscle cells
Ciliated respiratory epithelium
No cellular atypia.
Architectural Patterns:
Lobular architecture
Cartilage predominant
Cleft-like spaces lined by epithelium
Fibrous septa
Calcification common.
Grading Criteria:
Benign lesion
No grading applicable
Assessment: Tissue components
Cellular maturity
No atypia or mitoses.
Immunohistochemistry
Positive Markers:
HMGA2 - positive (chromosomal rearrangements)
S-100 - positive (cartilage)
Smooth muscle actin - positive (muscle)
CK7 - positive (epithelium).
Negative Markers:
p53 - negative
Ki-67 - very low (<1%)
CDX2 - negative
TTF1 - negative (in stroma).
Diagnostic Utility:
HMGA2 helps confirm diagnosis
S-100 highlights cartilage
Low Ki-67 confirms benign nature
CK7 highlights epithelial component.
Molecular Subtypes:
All hamartomas: HMGA2 rearrangements common
Chondroid type: Prominent cartilage
Lipomatous type: Prominent fat
Mixed type: Multiple components.
Molecular/Genetic
Genetic Mutations:
HMGA2 rearrangements (65%)
HMGA1 rearrangements
Chromosome 12q13-15 alterations
PTEN mutations (Cowden syndrome)
Simple karyotype.
Molecular Markers:
HMGA2 overexpression
Growth factor independence
Normal cell cycle
No oncogene activation
Stable genome.
Prognostic Significance:
Excellent prognosis
No malignant potential
No metastases
Complete excision curative
Recurrence extremely rare.
Therapeutic Targets:
Surgical excision
Wedge resection
Endobronchial removal
Observation (small, asymptomatic)
No medical therapy needed.
Differential Diagnosis
Similar Entities:
Chondrosarcoma
Lipoma
Sclerosing pneumocytoma
Carcinoid tumor
Solitary fibrous tumor
Metastatic chondrosarcoma.
Distinguishing Features:
Hamartoma: Mature tissues, cleft-like spaces
Chondrosarcoma: Cytological atypia, mitoses
Lipoma: Pure adipose tissue
Pneumocytoma: Papillary, TTF1+
Carcinoid: Neuroendocrine markers+.
Diagnostic Challenges:
Small biopsies
Chondrosarcoma differentiation
Lipoma vs lipomatous hamartoma
Endobronchial sampling.
Rare Variants:
Lipomatous hamartoma
Myxoid hamartoma
Cystic hamartoma
Multiple hamartomas (Cowden).
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[Wedge resection/endobronchial biopsy] with nodule
Tumor Description
Well-circumscribed nodule measuring [X] cm with lobulated appearance
Microscopic Features
Benign lesion composed of mature cartilage, adipose tissue, and fibrous connective tissue
Tissue Components
Components: [Cartilage (predominant)/Adipose tissue/Fibrous tissue/Smooth muscle/Respiratory epithelium]
Epithelial Component
Cleft-like spaces lined by respiratory epithelium
Cellular Features
No cellular atypia or increased mitotic activity
Calcification
Calcification: [present/absent]
Final Diagnosis
Pulmonary hamartoma, [chondroid/lipomatous/mixed] type
Prognosis
Benign lesion with excellent prognosis. Complete excision is curative.