We reviewed 34 available bronchogenic cysts that were surgically resected at the Osaka Medical and Pharmaceutical University Hospital from 1998 to 2020. Representative hematoxylin and eosin (H&E)-stained sections were selected, and two pathologists reexamined the pathologic features and diagnoses. For the diagnosis of bronchogenic cysts, we used the Govaerts et al. anatomopathological criteria as outlined earlier in the Background section [2].
The phenotypes of the epithelium lining the cyst were characterized using IHC analysis as the methods described here. The tissue specimens were fixed in 10% neutral buffered formalin and embedded in paraffin wax for H&E staining. IHC analysis was performed using Vectastain Elite ABC kits from Vector Laboratories (Burlingame, CA, USA) according to the manufacturer’s instructions for blocking, dilution of secondary antibody, and labeling. Briefly, 4-µm-thick sections were cut from the paraffin block. After deparaffinization, endogenous peroxidase activity was quenched by incubation in 3% hydrogen peroxide solution for 10 min. Antigen retrieval was performed using a preheated target retrieval solution (pH 6.0) from Dako/Agilent for 30 min in a boiling rice cooker. The sections were then incubated with primary antibodies at room temperature for 60 min. 3,3-diaminobenzidine was freshly prepared from tablets (Sigma-Aldrich) for chromogenic staining at 20°C for 10 min.
As reagents, primary antibodies against CK7 (clone OV-TL 12/30), CK20 (clone Ks20.8), thyroid transcription factor 1 (TTF-1, clone 8G7G3/1), synaptophysin (Syp, clone SY38), and surfactant protein A (SP-A, clone PE10) were obtained from Dako/Agilent (Santa Clara, CA, USA). Anti-p40 (clone BC28) antibody for detecting basal cells was obtained from Nichirei (Tokyo, Japan). Anti-α-smooth muscle actin (αSMA, clone 1A) and napsin A (clone IP64) antibodies were obtained from Sigma-Aldrich (Tokyo, Japan) and Leica Biosystems (Buffalo Grove, IL, USA), respectively.
The locations of the 34 bronchogenic cysts are listed in Table 1. Many of them were located in the mediastinum or intrapulmonary region. We found several bronchogenic cysts in rare sites including the retroperitoneum, skin, spinal cord, or pericardial cavity; we then reconfirmed their diagnoses based on the Govaerts et al. criteria as described earlier, and characterized the epithelial phenotypes.
Retroperitoneal bronchogenic cyst
Two cases of retroperitoneal bronchogenic cyst were found. One was a mass and cystic lesion on the left side of the retroperitoneum in a 40-year-old woman, which was detected during a medical checkup (Fig. 1A). The patient was asymptomatic, and her medical and family histories were unremarkable. Laboratory data, including hormones (e.g., catecholamine), were within the normal range. Based on computed tomography (CT), a neoplastic disease in the adrenal gland was one of the differential diagnoses. Surgical excision of the lesion was performed to obtain a pathological diagnosis. The specimen was a brownish and soft mass lesion in addition to the left adrenal gland, and it measured 5.5 × 5.0 × 3.5 cm (Fig. 1B). The divided surfaces after the cross-sectioning revealed a multicystic lesion, including atmospheric gelatinous or light-yellow contents. Macroscopically, we found an intact adrenal gland (Fig. 1C), indicating that the lesion was not derived from it.
On microscopic examination, the cyst was lined with ciliated epithelium and separated from the intact adrenal gland (Fig. 1D and 1E). TTF-1, a marker preferentially expressed in thyroid follicle, bronchial, and alveolar epithelium, positively stained in the ciliated epithelium (Fig. 1F). We found the presence of seromucous glands (Fig. 1G), cartilage (Fig. 1H), and smooth muscle that was stained with anti-αSMA antibody (Fig. 1I and 1J) near the cystic lesion, which met the criteria for bronchogenic cyst. Considering these, the diagnosis of retroperitoneal bronchogenic cyst was confirmed.
Next, we characterized the epithelial phenotypes using IHC analyses. CK7 (a cytokeratin marker), TTF-1, p40, Syp (a neuroendocrine marker), napsin A, which is preferentially expressed in bronchial and alveolar epithelium, and SP-A (a material secreted by alveolar type II cells) showed positive staining in the ciliated epithelium (Fig. 2A, 2B, 2D–2H), whereas, staining was negative for CK20 (a cytokeratin marker; Fig. 2C). These IHC features were similar to those of the respiratory epithelium in that both were CK7-positive and CK20-negative (data not shown).
Another case involved a cystic lesion in the retroperitoneum of a 65-year-old man as shown in Supplemental Fig. 1 (Fig. S1). On microscopic examination, the cyst was lined with ciliated epithelium, and with smooth muscle (Fig. S1A), which met the criteria for bronchogenic cyst. In this case, seromucous glands and cartilage were not detected. IHC features were similar to those of the above-mentioned case of retroperitoneal bronchogenic cyst, in which the staining was positive for CK7, TTF-1, p40, napsin A, and SP-A (Fig. S1B, S1D to S1G) and negative for CK20 (Fig. S1C) in the ciliated epithelium. We reconfirmed the diagnoses of the two cases and found that the retroperitoneal bronchogenic cysts showed phenotypes similar to those of the respiratory epithelium.
Bronchogenic cyst in the skin
There were two cases of bronchogenic cyst in the skin. A 59-year-old man had a polyp-like lesion on the medial anterior chest since childhood, and it had grown with age (Fig. 3A). Chest CT showed a cystic lesion measuring 14.7 × 12.0 × 8.0 cm (Fig. 3B). Surgical excision of the lesion was performed to obtain a pathological diagnosis. As shown in Fig. 3C, the cyst wall was lined with ciliated epithelium (lower panel, light blue square), which was located in the deep dermal tissue (upper and middle panels). Seromucous glands were detected near the cyst wall (Fig. 3D). Goblet cells were also found among the cyst-lining cells (Fig. 3E). Epithelial phenotypes of ciliated epithelium were positive for CK7, TTF-1, and p40 (Fig. 3F–3H) and negative for CK20 (data not shown). Smooth muscle was found under the cyst, which was confirmed by αSMA-positive staining (Fig. 3I). Although cartilage was not found in this case, a diagnosis of bronchogenic cyst was made based on the presence of ciliated epithelium, seromucous glands, and smooth muscle.
Another case was a small polyp-like lesion on the chest of a 1-year-old boy (Fig. S2A). Microscopic examination revealed a multicystic lesion in the dermis (Fig. S2B). The ciliated epithelium with goblet cells lined the cyst, in addition to seromucous glands and cartilage (Fig. S2C and S2D), and showed positive staining for CK7, TTF-1, and p40 (Fig. S2E to S2G), and negative staining for CK20 (data not shown). In this case, smooth muscle was not detected. Based on these findings, we confirmed the diagnosis of bronchogenic cysts in the skin.
Bronchogenic cyst in the cervical spinal cord and pericardial cavity
As shown in Fig. 4, a nodular lesion was detected on magnetic resonance imaging in the cervical spinal cord (C4–5) of a 12-year-old boy (Fig. 4A). He had pain and numbness in the left shoulder and upper arm, which had persisted for a month before he visited an orthopedist. Upon medical examination, he displayed loss of muscle strength in the left upper and lower extremities. Spinal cord neoplasm was a differential diagnosis, and surgical excision of the lesion was performed. The H&E section showed a multicystic lesion (Fig. 4B) that was lined with ciliated epithelium (Fig. 4C). Epithelial phenotypes of the ciliated epithelium were positive for CK7 and p40 (Fig. 4D and 4G) and negative for CK20 and TTF-1 (Fig. 4E and 4F). Smooth muscle was found under the cyst, which was confirmed by αSMA-positive staining (Fig. 4H), resulting in the diagnosis of a bronchogenic cyst. Seromucous glands and cartilage were not detected.
A 56-year-old man underwent surgery for mitral regurgitation. During the surgery, a cystic lesion was incidentally found in the pericardial cavity. On microscopic examination, it was lined with ciliated epithelium, with seromucous glands and cartilage (Fig. 5A and 5B). Epithelial phenotypes of ciliated epithelium were positive for CK7, TTF-1, p40, and Syp (Fig. 5C, 5E to 5G), but were negative for CK20 (Fig. 5D). Smooth muscle was found under the cyst, which was confirmed by αSMA-positive staining (Fig. 5H), resulting in the diagnosis of a bronchogenic cyst.