History
    This patient suffered from left chest pain since Octber 1997. She had not any medical problem before.  Plain chest PA revealed a SPN on left lower lug field. Bronchofiberscopy revealed no gross abnormality. AFB smear of bronchial washing fluid was negative but tuberculous antigen was positive on PCR test.  Presumptive diagnosis of pulmonary tuberculosis was given and she was treated under anti-tuberculosis drug. But follow up check of chest PA in February 1998 showed slight increase of size of the SPN, so chest CT was taken.

Lab; CBC 4600/11.7/35.6/269,000
     PFT mild restrictive type

Findings
     Plain radiograph revaeled a SPN with spiculated margin on left retrocardiac area.. Follow up check of chst PA 3 months later refealed slight increase of the SPN, but its nature was not changed.  The mass rather looked as subsegmental collapse-consolidation with considerable contrast enhancement. Low attenuation with well-defined border within the lesion simulates mucoid impaction or necrotic cavity. The extrapleural space is widened adjacent to the lesion and a dilated vessels shadows within.

Discussion
Pulmonary sequestration is defined as a segment of lung parenchyma separated from the normal bronchial tree and its blood supply from systemic artery.  Three quarters of the cases are intralobar sequstration, and the most occurred in the lower lobe, usually on the left. The main pathologic changes are chronic inflammation, cystic changes and fibrosis, The anomalous arterial feeder is usually located in the inferior pulmonary ligament. The radiographic findings varied on the pathology, 1) relatively homogenous consolidation or mass-like shadow, 2) persistent or recurrent pneumonia in the lower lobe, 3) single or muti-cystic shadow with or without air-fluidlevel along with the progress of inflammation. Rarely it may present as localized emphysema, left-to-right shunt simulaing pulmonary AVM or calcified mass  Differential diagnosis includes lung abscess, necrotizing pneunomia, fungal or tuberculous infection in case of cavitary lesion, or bronchiectasis, emphysema, pneumatocele, bronchogenic cyst, CCAM, diaphragm herniation or eventration in case of multi-cystic lesion.

References
1. Pulmonary sequestration: six unusual presentations AJR 1980;134:695-700
2. The continum of pulmonary developmental anomalies. Radiographics 1987;747
3. Imaging of pulmonary sequestration. AJR 1990;154:241-249
4. Intralobar sequestration: Radiologic-pathologic correlation. Radiographics 1997;17:725-745