Mycetoma

A rare example of an intralobar sequestration (ILS) containing a fungal mycetoma is reported. This finding indicates the presence of a communication between the ILS and the airways, thus supporting the theory that ILSs are acquired lesions, rather than congenital malformations.

Sequestrations are rare anomalies in which local areas of lung receive systemic arterial supply and lack normal communication with the tracheobronchial tree.[1-4] They may occur within the normal pleural covering of the lung (intralobar sequestration [ILS]) or external to the pleura surface (extralobar sequestration). While extralobar sequestrations are generally considered congenital in origin, there is considerable debate regarding the pathogenesis of ILS, and the theory that ILS is an acquired, rather than a congenital, defect has gained popularity.[3] We report the rare occurrence of a fungal mycetoma within an ILS and discuss implications for the pathogenesis of this anomaly.

Case Report

A 36-year-old white woman was referred to our institution because of an enlarging mass in the lower lobe of the left lung. Twelve months previously, she had experienced left back pain radiating to her left shoulder associated with dyspnea on exertion, easy fatigability, and fever. A chest radiograph showed a well-defined, homogeneous density in the left lower lobe adjacent to the descending aorta, and a computed tomographic scan localized the mass to the posterior basal segment of the left lower lobe. Bronchoscopy revealed normal endobronchial anatomy. No communications were seen between the bronchi and the mass. Angiography demonstrated a separate blood supply to the lesion from an abnormal artery arising from the inferior phrenic artery (off the celiac axis).

Thoracotomy was performed, revealing a large mass in the left lower lobe with a 3- to 4-mm-diameter feeding artery in the inferior pulmonary ligament originating below the diaphragm. The artery was ligated and divided, and a left lower lobectomy was performed. The patient experienced an uneventful recovery.

Pathologic Findings

The specimen consisted of a left lower lobe weighing 230 g and measuring 12.0 x 10.5 x 5.0 cm. The visceral pleura was thin and glistening except in a 5.0 x 5.0-cm area at the base, where it was thickened by fibrofatty adhesions. A 1.5-cm-long segment of thickwalled artery measuring 0.4 cm in diameter was noted to enter the lung in this area.

Upon sectioning the lung, a 6.0 x 5.0 x 5.0-cm white to yellow, sharply demarcated, multiloculated cystic area was found in the posterior basal segment (Fig 1). The component cysts ranged in diameter from 0.3 to 4.5 cm, and many contained thick white to yellow purulent-appearing material. Embedded within this material in some of the cysts, but not attached to the cyst walls, were multiple small, 0.5- to 1.0-cm light brown to green, soft spherical masses. The large artery noted on the pleura overlying the cystic area could be traced to the center of the lesion. No gross evidence of communication between the bronchial tree and the cystic lesion could be found. The remaining lung parenchyma away from the cystic lesion was normal.

On microscopic examination, the cysts were lined by pseudostratified, ciliated columnar respiratory tract epithelium that was focally ulcerated. There was a thin rim of interstitial fibrosis and chronic inflammation surrounding the cystic area. An exudate containing acute inflammatory cells was present in some cysts. The grossly noted green-brown spheres were small mycetomas composed of densely packed fungal hyphae arranged in lamellae, morphologically resembling Aspergillus species (Fig 2). No evidence of fungal invasion into adjacent lung tissue was found.

Discussion

Recurrent infections are common complications of ILS, and often are the first manifestations of this anomaly. They are usually caused by common bacteria, although tuberculosis and nocardiosis have been implicated occasionally.[1,3,4] Most infections in ILS can be explained either by the presence of collateral ventilation between the airspaces of the ILS and adjacent lung parenchyma or by bloodstream seeding during bacteremia. Fungal mycetomas complicating ILS, as occurred in our patient, have been reported only rarely, and are more difficult to explain.[5]

Mycetomas are aggregates of fungal hyphae, most often Aspergillus species, occurring within previously abnormal, usually cystic areas of lung. The airways are thought to be the source of infection, since Aspergillus commonly resides in these structures even in normal individuals. The occurrence of a fungal mycetoma within an ILS indicates that the ILS must have some connection with the tracheobronchial tree, and in fact, such communications have been documented by bronchography in a few cases.[2] Their presence supports Stocker's theory[3] that ILSs are acquired lesions related to chronic infection, rather than being congenital abnormalities related to abnormal development of the lung bud (in which case connection with the airways would be absent). According to this theory, the systemic arterial supply of an ILS results from hypertrophy of normally occurring arteries in the inferior pulmonary ligament, and residual communication with the bronchial tree could occur depending on the extent and chronicity of the infection.

References

[1] Fraser RG, Pare JAP, Pare PD, Fraser RS, Genereux GP. Diagnosis of diseases of the chest, 3rd ed. Philadelphia: WB Saunders, 1989; 701-12

[2] Gustafson RA, Murray GF, Warden HE, Hill RC, Rozar GE. Intralobar sequestration: a missed diagnosis. Ann Thorac Surg 1989;47:841-47

[3] Stocker JT. Sequestrations of the lung. Semin Diagn Pathol 1986; 3:106-21

[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] Hwang JJ, Wang TH, Wu CC, Chang CY. Bronchopulmonary sequestration associated with aspergilloma, with special reference to the finding of radionuclide venoangiography. Jpn J Med 1985; 2:164-68

COPYRIGHT 1993 American College of Chest Physicians
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