Characteristics of pulmonary cysts in Birt–Hogg–Dubé syndrome: Thin-section CT findings of the chest in 12 patients

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Abstract

Purpose

To describe in detail the characteristic chest computed tomography (CT) findings of Birt–Hogg–Dubé (BHD) syndrome.

Materials and methods

Thin-section chest CT scans of consecutive 12 patients with genetically diagnosed BHD syndrome were retrospectively evaluated by two observers, especially about the characteristics (distribution, number, size, shape and relation to pleura) of pulmonary cysts. Interobserver agreement in the identification of abnormalities on the CT images was achieved using the κ statistic, and the degree of interobserver correlation for the characterization of pulmonary cysts was assessed using the Spearman rank correlation coefficient.

Results

Multiple pulmonary cysts were seen in all patients. The number of cysts in each patient was various (range, 29–407), and cysts of various sizes (from a few mm to 2 cm or more) were seen in all patient. 76.6% (mean) of cysts were irregular-shaped, and 40.5% (mean) of cysts were located along the pleura. The mean extent score of cysts was 13% of the whole lung, and the distribution of cysts was predominantly in the lower medial zone. Finally, cysts abutting or including the proximal portions of lower pulmonary arteries or veins were also seen in all patients.

Conclusion

Multiple, irregular-shaped cysts of various sizes with lower medial lung zone predominance are characteristic CT findings of BHD syndrome. Cysts abutting or including the proximal portions of lower pulmonary arteries or veins may also exist in this syndrome in a high probability.

Introduction

Birt–Hogg–Dubé (BHD) syndrome is a rare autosomal dominant inherited genodermatosis and characterized by clinical manifestations including hamartomas of the skin (fibrofolliculomas, trichodiscomas, acrochordons, etc.), renal tumors (chromophobe renal cell carcinoma, oncocytoma, hybrid chromophobe-oncocytomas, clear cell carcinoma, papillary renal cancer, angiomyolipoma, etc.) and pulmonary cysts with spontaneous pneumothorax [1], [2]. The BHD gene, a tumor suppressor gene located in chromosome 17p11.2, has recently been identified to be defective in patients with BHD syndrome [3].

Toro et al. reported that 24% of their patients had a history of spontaneous pneumothorax, and pulmonary cysts, skin fibrofolliculomas and renal tumors were found in 89%, 98% and 23%, respectively [4]. Patients with BHD syndrome do not always have all three manifestations (skin, lung and kidney), and sometimes have only multiple pulmonary cysts without any other features [2], [5]. Zbar et al. described that the frequency of fibrofolliculomas and renal tumors increased after 20 and 40 years of age, respectively, while the frequency of spontaneous pneumothorax increased between 20 and 40 years of age and decreased after more than 40 years of age [6]. Among the previously published case reports, the youngest case of BHD syndrome with spontaneous pneumothorax was 7 years of age [7]. Based on these reports, it appears that the majority of patients with BHD syndrome have pulmonary cysts, and pulmonary cysts may develop earlier than the skin and renal manifestations. In this context, the detection of pulmonary cysts may be useful for early diagnosis of this syndrome, and chest computed tomographic (CT) scanning may play an important role. By the early detection of this syndrome, it will be possible to follow up the patients and their family with care to renal tumor and pneumothorax which can affect prognosis and quality of life.

Although the chest CT appearance of BHD syndrome has been described by other groups [6], [9], [10], to our knowledge little has been described in detail about that. The objective of the present study is to describe in detail the characteristic chest CT findings of BHD syndrome.

Section snippets

Study population

This retrospective study was approved by the ethics committees of our institutes. Written informed consent was obtained from all subjects as required. We enrolled 12 consecutive patients who had a definitive diagnosis of BHD syndrome and who had undergone thin-section CT between January 2002 and December 2007 in our institute. All patients were referred to our institution for detailed examination about their recurrent pneumothorax or multiple pulmonary cysts on chest-X ray. The study subjects

Results

The assessments for the presence of pulmonary cysts and other findings were completely agreed between two observers (κ = 1), and multiple pulmonary cysts (Fig. 2) were only CT finding in all patients.

The overall result of the number of pulmonary cysts identified in each assessment category (anatomic distribution, size, shape and relation to pleura), and the interobserver correlation are summarized about these assessments in Table 2. All of the interobserver correlations were significant (r = 

Discussion

In this study, we showed that the characteristic chest CT findings of patients with BHD syndrome were multiple thin-walled pulmonary cysts of various sizes, predominantly distributed to the lower medial and subpleural regions of the lung with cysts abutting or including the proximal portion of lower pulmonary veins or arteries. We also showed that the extent of pulmonary cysts in BHD syndrome did not change over time although the number of patients examined is limited.

Toro et al. reported that

Acknowledgements

This study was supported by Grant-in-Aid for Scientific Research No. 18659242 (Kuniaki Seyama); in part by the High Technology Research Center Grant from the Ministry of Education, Culture, Sports, Science, and Technology, Japan; and in part by the Institute for Environmental and Gender-Specific Medicine, Juntendo University, Graduate School of Medicine.

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