Pulmonary sequestration

A rare case of intralobular pulmonary sequestration (ILS) with three aberrant arteries occurred in a 75-year-old woman. A contrast-enhanced chest CT scan demonstrated a paraaortic, partially enhanced mass shadow and two small liner enhancements in the upper portion of the mass. A definitive diagnosis could not be rendered with a CT scan alone, hut the findings suggested bronchopulmonary sequestration with multiple aberrant arteries. Surgery confirmed three fine aberrant arteries arising from the thoracic aorta and entering the left lower lobe basal segment. Judging from the patient's age and multiple aberrant arteries, the sequestrated lung appeared as if it were acquired. However, all aberrant arteries were of the elastic type histologically. This finding suggested that ILS was not an acquired condition but a congenital malformation. (CHEST 1998; 114:936-938)

Key words: aberrant artery; bronchopulmonary sequestration; congenital malformation; elastic laminae

Abbreviations: ILS=intralobar pulmonary sequestration

Bronchopulmonary sequestration, intralobar or extralobar, is a relatively rare abnormality. Intralobar pulmonary sequestration (ILS) is defined as a dysplastic area of the lung without communication to the tracheobronchial tree that derives its blood supply from systemic vessels. ILS initially occurs most often in young adults or adolescents and is rarely seen in patients over 40 years of age. The vascular supply from a systemic artery is generally single and arises from the thoracic aorta. It remains controversial whether the origin is congenital or acquired. In this article, a 75-year-old patient with ILS involving three aberrant arteries is reported, and the origin and pathogenesis of this condition are discussed.

CASE REPORT

A 75-year-old woman was hospitalized for medical evaluation of an abnormal shadow observed on an annual routine chest roentgenogram. She had a 3-year history of recurrent acute bronchitis with dry cough and fever.

Standard chest roentgenograms revealed a shadow of a round tumor in the left posterior basal segment (S10). A CT scan using a bolus venous injection demonstrated a shadow of a paraaortic mass with small linear enhancements (Fig 1). Initially, these small structures were thought to he neovascularities entering a lung tumor. However, from her history and the tumor location, the possibility of bronchopulmonary sequestration and aberrant arteries was considered. Bronchoscopy revealed stenosis of the left basal bronchus, and cytologic examination of transbronchial tumor brushing was negative for malignant cells. Findings on aortography were not dear regarding aberrant arteries. There were no significant abnormalities. At surgery, three small pulsating aberrant arteries were identified. Two were 2 mm and 1 was 3 mm in diameter. These arose from the descending thoracic aorta and entered the left basal segment but the pulmonary ligament was not thickened (Fig 2). Since no malignant cells were detected by intraoperative cytologic study with aspiration of the tumor, left basal segmentectomy was performed. On the cut specimen, the consolidated segment containing multiple small cysts accompanied by a major cyst, measuring 35 x 25 x 25 mm, was filled with mucoidal material. Intraoperative histopathologic frozen section study of the cyst and the fluid material did not indicate malignancy. Histopathologic examination showed that the configuration of the cysts indicated ectatic bronchi. The aberrant arteries were elastic without intimal thickening or atherosclerotic changes (Fig 3). Thus, the patient was diagnosed with Price III type ILS. The patient made an uneventful recovery from surgery.

[Figures 1-3 ILLUSTRATION OMITTED]

DISCUSSION

Bronchopulmonary sequestrations are fairly uncommon anomalies. The condition is anatomically divided into two forms, ILS and extralobar sequestration. ILS exists when dysplastic tissue is encased within the normal visceral pleura of the lung, while the extralobar condition exists when the tissue mass has its own pleura. ILS accounts for 75% of pulmonary sequestrations. The lesion consists of lung tissue that lacks normal communication to the tracheobronchial tree, has a systemic arterial supply, and shares the pleura of the parent lobe. Onset usually occurs before the age of 40 with recurrent infection.[1] This ease was initially considered to be a tumor rather than pulmonary sequestration because the patient was advanced in age.

The cause of ILS is unknown, but ILS has generally been considered to be a congenital malformation. The most commonly accepted hypothesis is that the sequestered lung represents an accessory lung bud that has maintained its own systemic blood supply.[2] Some authors have proposed that ILS represents an acquired lesion, subsequent to bronchial obstruction, pneumonia, pulmonary artery occlusion, pleuritis, pulmonary ligament thickening, and parasitization of pulmonary ligament arteries.[3] The latter hypothesis seems reasonable since this patient was advanced in age, and the lung tissue surrounding the sequestration was inflamed. In the reported ease, the three aberrant arteries were all fine in diameter, and the pulmonary ligament was not thickened. Therefore, if the sequestrated lung in this ease was acquired, it was recently formed. However, pathologically all aberrant arteries were of the elastic type without a muscular layer, and there were no findings of pulmonary artery occlusion or atherosclerosis. Since the pulmonary ligament artery is originally the muscular type, and there is no evidence to suggest that a muscular-type artery can transform into an elastic type, one cannot accept that the pulmonary ligament arteries led to the "creation" of ILS as described by Stocker and Malczac.[4] There has been some confusion between chronic bronchiectasis with enlarged bronchial arteries due to inflammation and ILS with aberrant arteries. In this ease, ILS with cystic appearance could be easily confused with chronic bronchiecctasis. However, as ILS is a congenital lesion but most eases of chronic bronchiectasis without symptoms in childhood are acquired, it must be concluded that the aberrant artery of ILS is the elastic type, and the enlarged bronchial artery of chronic bronchiectasis is of the muscular type. Ishida et al[3] have reported that ILS in children was classified into two groups, the central type and the peripheral type, according to the reconstruction of the bronchial tree in the sequestrated lung. They claimed that the peripheral type is the true ILS, and the central type is a mixture and a sequela of another disease such as bronchial atresia. The former type in segment 10 areas and aberrant arteries was elastic in histologic nature. The latter type in variable sites of the lesion and arteries was muscular. It is suggested that characteristics of an aberrant artery would be useful for the definitive diagnosis of ILS to avoid confusion with other acquired diseases regardless of the anatomic appearance or the patient's age.

Preoperative diagnosis of ILS is difficult. Savic et al[1] indicated that ILS was suspected or diagnosed preoperatively in only 47 of 100 cases, while extralobar sequestration was preoperatively diagnosed in only 6 of 66 cases. Differential diagnostic possibilities include bronchiectasis, lung abscess, empyema, lung neoplasm, congenital cystic adenomatoid malformation, staphylococcal pneumonia with pneumatocele formation, and congenital diaphragmatic hernia (Bochdalek's hernia). Traditionally, the diagnosis of ILS has been performed by angiography to confirm the aberrant arterial and venous drainage. In the reported ease, aortography was not definitive. Diagnostic findings could not be obtained because all aberrant arteries were fine pulmonary ligament arteries. MRI,[5] CT scans with contrast enhancement as in this ease, and spiral CT scans are useful in selected cases. In the CT with contrast enhancement, small linear enhancements with a tumor shadow in the left posterior basal segment near the descending aorta were obtained. Therefore, ILS was suspected.

Surgical treatment is recommended for ILS, not only in symptomatic cases but also in asymptomatic cases because the sequestration may cause complications, such as infection, pulmonary hemorrhage, pulmonary hypertension, and cardiac failure. Though there are many procedures available for surgical resection, it is necessary to select a procedure appropriate for resecting a completely inflamed segment. Such a procedure as lobectomy or segmentectomy with careful ligation of the aberrant arteries if possible would qualify.[6] In this ease, segmentectomy was selected based on the patient's respiratory function and age.

This 75-year-old patient was diagnosed with Price III type ILS postoperatively. All three aberrant arteries were the elastic type. This report suggests that ILS is not an acquired condition but a congenital malformation due to the histologic findings of aberrant arteries and emphasizes that ILS should be considered, even in patients with advanced age.

REFERENCES

[1] Savic B, Birtel FJ, Tholen W, et al. Lung sequestration: report of seven cases and review of 540 published cases. Thorax 1979; 34:96-101

[2] Blesovsky A. pulmonary sequestration: a report of an unusual case and a review of the literature. Thorax 1967; 22:351-357

[3] Ishida H, Hajikano H, Hayashi A. Intralobar sequestration in children--a new concept from the form of bronchial tree in sequestrated lung. Nippon Kyobu Geka Gakkai Zasshi 1992; 40:957-968

[4] Stocker JT, Malczac HT. A study of pulmonary ligament arteries: relationship to intralobar pulmonary sequestration. Chest 1984; 86:611-615

[5] Doyle AJ. Demonstration of blood supply to pulmonary sequestration by MR angiography. AJR Am J Roentgenol 1992; 158:989-990

[6] Haller JA, Golladay ES, Pickard LR, et al. Surgical management of lung bud anomalies: lobar emphysema, bronchogenic cyst, cystic adenomatoid malformation, and intralobar pulmonary sequestration. Ann Thorac Surg 1979; 28:33-43

(*) From the Department of Thoracic Surgery, Ishikawa Prefectural Central Hospital, Kanazawa, Japan.

Manuscript received December 16, 1997; revision accepted March 25, 1998.

Correspondence to: Yoshio Tsunezuka, MD, PhD, Department of Thoracic Surgery, Ishikawa Prefectural Central Hospital, Kanazawa, 920, Japan

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