대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Extralobar Pulmonary Sequestration

Radiologic Findings

Chest radiograph shows a well-defined mass shadow in the left hilar region.

Pre- and postcontrast CT scans show a 5-cm-sized, homogeneous low attenuation mass in the left mediastinum without contrast enhancement.

Excision of the cystic mass was done.
No significantly enlarged arterial feeder originating from the descending thoracic aorta was seen on enhanced CT scan or during the surgery.

Pathologic specimen revealed cartilage-bound bronchial structures with bronchioles and alveoli, suggestive of extralobar pulmonary sequestration.

Pathologic Note: This cyst has a structure of bronchioles and alveoli in addition to bronchus structure. These histologic findings are not compatible with bronchogenic cyst and the possibility of sequestration is most likely considered.

Brief Review

Pulmonary sequestration is an uncommon congenital anomaly encountered in approximately 1.1-1.8 % of all pulmonary resections (1-2). Theses lesions consist of maldeveloped lung tissue that lacks a normal connection to the tracheobronchial tree (and is therefore typically separate from normal lung) and derives its blood supply from systemic vessels. Classically, it has been described in two forms: (1) intralobar sequestration, in which the sequestered part of the lung lies within normal pulmonary visceral pleura, and (2) extralobar sequestration, in which the abnormal segment of the lung is completely separate and enclosed in its own pleural investment. The arterial supply is systemic and venous return is either by a pulmonary vein (in the intralobar form) or by a systemic vein (in the extralobar form) (1, 3). Pulmonary sequestration is generally thought to be congenital (4), although some authors have argued that intralobar sequestrations may be acquired (1, 5).

Extralobar sequestration accounts for 25 % of all classic pulmonary sequestrations (5). A majority of cases (61 %) occur in the first 6 months of life, often presenting in the first day of life with dyspnea, cyanosis, and feeding difficulties. Extralobar sequestration is typically in the lower hemithorax (3, 4). The typical location is within the pleural space in the posterior costodiaphragmatic sulcus between in the diaphragm and the lower lobes (63-77 %) of cases (1, 5). However, it can also occur in the mediastinum, within the diaphragm, and, rarely, below the diaphragm (1). It has an even greater left-side preponderance (over 80 %) (1, 3, 4). Whereas, intralobar sequestration is almost always located posterobasally in the lower lobe, with a left-side preponderance (58 %) (3, 6). The demonstration of a systemic arterial supply to the lesion is the critical diagnostic feature of extralobar sequestration. The anomalous artery or arteries typically arise from the thoracic aorta (less often from the abdominal aorta) in approximately 80 % of cases and enter the lung via the pulmonary ligament (1, 3, 5). In 15 % of cases, the lesions are supplied by smaller arteries such as splenic, gastric, subclavian, or intercostal arteries. Branches of the pulmonary artery supply the lesions in 5 % of cases. The venous drainage is usually systemic (80%), through the azygos and hemiazygos system, or the vena cava to the right atrium. In about 25 % of the lesions are drained through the pulmonary veins (1, 5).

Radiographically, extralobar sequestration manifests as a single, well-defined, homogenous, triangular opacity typically located in the lower thorax in close association with the posterior medial hemidiaphragm. The lesion may manifest as a mass elsewhere in the thoracic cavity, including the upper thorax, the mediastinum, and the paravertebral region (1). Other findings include normal-appearing lung, hyperlucent areas, and combination of solid and cystic masses and pneumonia (3. 7). CT of the chest characteristically demonstrates extralobar sequestration as a homogenous, well-circumscribed mass of soft-tissue attenuation (1). Emphysematous changes of the adjacent nonsequestered lung have been described. CT may demonstrate cystic areas within the extralobar sequestration (1, 3). The anomalous systemic artery is visualized less frequently (1).

Ikezoe et al (3) reported the CT findings of the pulmonary sequestration with 24 cases. They classified lung abnormalities shown by CT into three types: A= cysts containing air or fluid or soft tissue masses; B= emphysematous lung surrounding cysts, and/or soft tissue nodules; and C= lung hypervascularity. Among the eight extralobar sequestrations in their study, all but one extralobar sequestration had pulmonary cysts (n=1) or emphysema (n=6) in the lung tissue immediately adjacent to the sequestration (type B). In these patients, four had mediastinal cystic masses. In their study, supplying arteries could be demonstrated at CT in 16 of 24 sequestrations including intra- and extralobar types.

The treatment of symptomatic or large asymptomatic sequestrations is surgical resection. Extralobar sequestrations with their separate pleural investments can usually be removed sparing normal lung, tissue, although in intralobar type, segmental resection or even lobectomy will be necessary (1, 2).

References

1. Rosado-de-Christenson ML, Frazier AA, Stocker JT, Templeton PA, Extralobar sequestration: radiologic-pathologic correlation. RadioGraphics 1993; 13:425-441
2. Piccione W, Burt ME. Pulmonary sequestration in the neonate. Chest 1990; 97:244-246
3. Ikezoe J, Murayama S, Godwin JD, Done SL, Verschakelen JA. Bronchopulmonary sequestration: CT assessment. Radiology 1990; 176:375-379
4. Savic B, Birtel FJ, Tholen W, Funke HD, Knoche R. Lung sequestration: report of seven cases and review of 540 published cases. Thorax 1979; 34:96-101
5. Felker RE, Tonkin ILD. Imaging of pulmonary sequestration. AJR 1990; 154:241-249
6. Landing BH, Dixon LG. Congenital malformations and genetic disorders of the respiratory tract. Am Rev Respir Dis 1979; 120:151-185
7. Durnin RE, Lababidi Z, Butler C, Selke A, Flege JB. Bronchopulmonary sequestration. Chest 1970; 57:454-459

Keywords

Lung, Congenital,