1. FLASHPATH
H a z e m A l i

2. MESENCHYMAL
CYSTIC HAMARTOMA
H a z e m A l i

3. CLINICAL
• Very rare
• Benign
• Indolent course
– Takes many years to become clinically evident (age range 1 – 50 years)
– Creates little disability, even when they are numerous and large
• Can present with cough, chest pain, spontaneous pneumothorax
• May represent the missing link between the higher forms of “cystic
adenomatoid transformation” and the lower forms of “pleuropulmonary
blastoma”

4. GROSS
• Bilateral
• Multiple
• Cysts (arrowhead) and nodules (arrows)
– Cysts are variably sized, thin-wall

5. MICROSCOPY
• Cysts:
– Lining: Respiratory epithelium
• “pseudostratified columnar ciliated”
– Wall: Cambium layer
• “primitive mesenchymal cells”
• Nodules:
– Solid growth of the same primitive mesenchymal cells
• Mature stromal components (e.g., cartilage, smooth muscle, or fat) can be focally
seen
• Neither the epithelial nor the mesenchymal cells had malignant features

6. DIFFERENTIAL DIAGNOSIS
“ O t h e r c o n g e n i t a l / c y s t i c l u n g d i s e a s e s ”
• Congenital:
– Bronchogenic cysts
– Congenital pulmonary cysts
– Congenital pulmonary airway malformation “especially type 4”
– Congenital lobar emphysema
– Pulmonary sequestration
• Acquired:
– Emphysema
– Healed abscess
– Honeycombing
• Mixed:
– Cystic fibrosis

7. DIFFERENTIAL DIAGNOSIS
Pleuropulmonary Blastoma
• Occur at an early age (median age of 2 years at presentation)
• Have both cystic and solid lesions macroscopically
• The cyst is composed of small primitive malignant cells lined by normal
respiratory epithelium
• Unlike MCH, the mesenchymal cells have high proliferating activity
– foci of differentiated sarcomatous elements (e.g., rhabdomyosarcoma,
chondrosarcoma, or osteosarcoma) may be found

8. DIFFERENTIAL DIAGNOSIS
Pulmonary hamartoma
• Solitary
• Solid nodule (No cysts)
• Formed of mature mesenchymal tissue (Not primitive)
• Nodules are separated by clefts lined with respiratory epithelium

9. DIFFERENTIAL DIAGNOSIS
In females, metastatic low-grade endometrial stromal sarcoma
must be excluded before diagnoses of mesenchymal cystic
hamartoma

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H a z e m A l i