Bronchogenic cyst is a congenital disease secondary to abnormal budding of the bronchial tree during embryonic development. It usually develops in the mediastinum and is rarely seen in the lung parenchyma. A diagnosis is often made before surgery because of its typical cystic appearance in computed tomography (CT) scan and magnetic resonance imaging (MRI) scan. We herein report a case of intrapulmonary bronchogenic cyst mimicking primary lung cancer with unusual radiological findings.

A 71-year-old female demonstrated an abnormal shadow in the right lung on a chest X-ray. She had no symptoms or remarkable history. Enhanced chest CT scan revealed an irregular nodule in the right upper lobe with a pleural indentation-like appearance and a heterogeneous enhancement suggesting the primary lung cancer but benign cyst (Figure 1). Positron emission tomography (PET) scan was not available then. MRI scan of brain and abdominal CT scan revealed no metastatic lesions. Although a transbronchial biopsy could not yield a histological diagnosis, we strongly suspected the lesion was non-small cell lung cancer (T2aN0M0 stage l B) and planned surgery with diagnostic and therapeutic intent. She underwent right upper lobectomy without needle aspiration to avoid bleeding or air embolism because the lesion located close to the hilar structures. The cut surface of the surgical specimen revealed a cystic appearance circumscribed by a thickened wall and intraoperative frozen examination showed no malignancy. The postoperative course was uneventful and she was discharged on the seventh postoperative day.

Histological examination revealed that the cyst wall contained cartilage, smooth muscle, and glandular tissue, confirming a diagnosis of intrapulmonary bronchogenic cyst (Figure 2A). The cyst wall also contained hyalinized fiber and mild lymphocyte infiltration, suggesting a past infection that might have caused the irregular radiological findings (Figure 2B).

Bronchogenic cyst is one of the bronchopulmonary malformations that result from an abnormal budding of the tracheobronchial tree [1]. It usually develops in the mediastinum and is rarely seen in the lung. Its typical cystic appearance can be visualized on CT scan and MRI scan [2]. However, we misdiagnosed the present case as primary lung cancer because of its distribution in the lung and the radiological findings suggested malignancy rather than a benign cyst due to an irregular shape and a heterogeneous enhancement. Histological examination revealed hyalinized fibrous tissue and lymphocyte infiltration along the cyst wall. Although the present patient had no remarkable history of pneumonia, a latent infection in the past might have caused these histological changes and resulted in the unusual radiological findings mimicking lung cancer.

Surgical resection is required both in stage l non-small cell lung cancer and bronchogenic cyst [2][3]. Although the present patient underwent lobectomy, we could have chosen a lung-sparing approach based on a preoperative diagnosis of the cyst [4]. We should have performed chest MRI scan in this case because it is useful not only in detecting a cyst but also in differentiating malignancy from benign tumors as PET scan was not available [5].

Even an asymptomatic bronchogenic cyst might have been affected by an infectious event in the past, and could reveal a variety of atypical radiological findings. Therefore, bronchogenic cyst should be raised as a differential diagnosis for an undiagnosed lung lesion.

We thank Mr. Ohta, a staff of academic and public relations office of Seirei Hamamatsu General Hospital, for converting the radiological films into the file formats.

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