FLASHPATHH a z e m A l i

MESENCHYMAL CYSTIC

HAMARTOMAH a z e m A l i

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”

GROSS• Bilateral

• Multiple

• Cysts (arrowhead) and nodules (arrows)– Cysts are variably sized, thin-wall

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

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

DIFFERENTIAL DIAGNOSISPleuropulmonary 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

DIFFERENTIAL DIAGNOSISPulmonary hamartoma• Solitary

• Solid nodule (No cysts)

• Formed of mature mesenchymal tissue (Not primitive)

• Nodules are separated by clefts lined with respiratory epithelium

DIFFERENTIAL DIAGNOSISIn 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