A 72-year-old asymptomatic male with 25 pack-year smoking history underwent low dose computed tomography (CT) of chest for lung cancer screening. The CT imaging reported a subcarinal mass (5.5 x 3.9 x 2.0 cm). Endobronchial ultrasound confirmed a 2 cm subcarinal mass at Station 7. A transbronchial fine-needle aspiration (TB-FNA) of the lesion was performed [Figure 1] that aspirated thick milky and cloudy fluid.
What is the most likely interpretation?
Metastatic carcinoma with cystic necrosis
Cystic hygroma (cavernous lymphangioma)
Esophageal duplication cyst
Ciliated lined cyst (bronchogenic cyst/ciliated foregut cyst)
Abscess
D. Ciliated lined cyst (bronchogenic cyst/ciliated foregut cyst)
The posterior mediastinal lesion was reported on CT scan as well demarcated smooth right subcarinal soft-tissue mass [Figure 2]. Aspirate from this lesion was thick and milky cloudy fluid with cytological features of ciliated lined cyst (bronchogenic cyst/ciliated foregut cyst) (Option d). It showed predominance of degenerated cellular debris admixed with scattered fragments of cells showing ciliary tufts [Figure 1]. These diagnostic cell fragments in this case were seen in direct smears but were few in number and required significant efforts to find them. Processing of the aspirate of such cystic lesion for cytopathological evaluation as liquid-based cytology (LBC) preparation (ThinPrep  or SurePath  or other similar method) or Cytospin  would concentrate detached ciliary tufts (degenerated debris with ciliated cellular fragments of cell tops without nuclei similar to ciliocytophthoria) and occasional intact ciliated cells so that they could be detected with relative ease. The cellular fragments with ciliary tufts could also be detected after diligent efforts in cell-block sections [Figure 3]. Cytomorphologically, these lesion cannot be distinguished from other ciliated lined cysts such as branchial cleft cyst and ciliated foregut cyst without clinicopathological and imaging correlation.
Metastatic carcinoma (Option A) as metastasis of carcinoma of lung, breast, thyroid, and genitourinary tract is relatively common to the mediastinum. Although most of the metastatic carcinoma present as a solid lesion, they can have a cystic component with coagulative necrosis as tumor diathesis, some viable diagnostic malignant cells are expected be found in the sample. It can be challenging to sample such lesions adequately during rapid on-site evaluation due to a high percentage of non-diagnostic necrotic component. Sampling from the periphery of the lesions increases the diagnostic yield. If the cystic lesion does not resolve completely after the aspiration of cyst contents, the residual lesion should be sampled adequately.
Cystic hygroma (cavernous lymphangioma) (Option B) usually occurs in children. It may be located in the neck or axilla, often extending into mediastinum, and rarely present in the lymph node. Large mediastinal lesions may compress lungs, heart, and nerves, even though most lesions are asymptomatic. Microscopically large and irregular lymphovascular spaces are lined by flattened and bland endothelial cells with variable proportion of fibroblastic collagenous stroma. The aspirates are usually hypocellular with relatively non-specific findings including scant endothelial cells with bland morphology with a few scattered lymphocytes and histiocytes in the background of amorphous proteinaceous material.[]
Esophageal duplication cysts (option C) are usually unilocular; however, they can be multiloculated with mucoid contents. Depending on the type of the cyst-lining, the aspirated cyst contents in addition to the debris show squamous, simple columnar, pseudostratified columnar, or mixed epithelial cells but are devoid of ciliated cells.
Abscess (Option E) shows purulent inflammation with predominance of neutrophils. Grocott-Gomori Methenamine Silver and Gram stain may show organisms such as fungi and bacteria. The organisms may also be seen with Diff-Quik stained direct smears and culture may grow causative organism(s).
What are the diagnostic features of bronchogenic cyst?
Contains tissues derived from all germ cell layers
Contains cartilage and smooth muscle in the wall
Typically lined by respiratory, cuboidal, and/or squamous epithelium
Lined by stratified squamous or gastrointestinal epithelium.
None of the above.
Cystic teratoma is lined by variable mixtures of gastrointestinal, squamous, and respiratory epithelium. It typically contains tissues derived from multiple germ cell layers. Some cases may contain immature tissue with nuclear atypia.
Thyroglossal duct cysts may be lined by respiratory epithelium; however, their cyst walls contain thyroid follicles and lack smooth muscle and cartilage.
Esophageal duplication cysts are lined by stratified squamous or gastrointestinal epithelium. They are usually found to be attached to the esophageal wall and have two smooth muscle layers.
Dermoid cysts are lined by stratified squamous epithelium, contain hair, and other skin appendages with keratinaceous or sebaceous material.
Abscess may mimic bronchogenic cyst. However, an abscess neither will have a true lining nor cartilage and smooth muscle in their wall. They, however, may contain foci of squamous metaplasia. The aspirates predominantly show suppurative material as numerous acute inflammatory cells with variable degenerative changes.
Branchial cleft cysts resemble bronchogenic cyst with ciliated lining; however, they may show squamous metaplasia and lymphoid aggregates with reactive germinal centers. They may also be filled with keratinaceous debris. In contrast to this, the bronchogenic cyst wall shows smooth muscle with variable proportion of seromucinous glands and hyaline cartilage (Option B).
Which of the following malignancies are reported in bronchogenic cyst?
Squamous cell carcinoma
Adenocarcinoma
Large cell carcinoma
Mucoepidermoid carcinoma
All of the above
Bronchogenic cysts are non-neoplastic hamartoma. However, similar to other anatomical tissues, rarely malignancy has been reported in bronchogenic cyst. The risk of malignancy in bronchogenic cyst is reportedly 0.7%.[] So far, the reported cases include large cell carcinoma, bronchoalveolar carcinoma, adenocarcinoma, schwannoma. mucoepidermoid carcinoma, and squamous cell carcinoma.
Pathophysiology of carcinogenesis in a bronchogenic cyst is not clear. One of the possibility is that the unstable epithelial cells in the cyst wall could have malignant potential leading to carcinoma. Whooley et al. reported squamous cell carcinoma of bronchogenic cyst in the paratracheal region.[] A few researchers have reported diaphragmatic bronchogenic cyst with mucoepidermoid carcinoma. Schwannomas are also reported in the wall of intrapulmonary bronchogenic cyst.
In the list mentioned below, which is the best diagnostic feature of a bronchogenic cyst?
Degenerated debris
Ciliated cell fragments
Intracystic proteinaceous material
Chronic inflammatory cells in a myxoid background
Numerous acute inflammatory cells
Being a cyst lined by ciliated epithelial lining, the aspirates from the cyst show debris of degenerated exfoliated lining cells with apical fragments of ciliated cells similar to ciliocytophthoria.
Bronchogenic cyst can be seen in which of the following location(s)?
Midline superficial supra-sternal
Lateral to the thyroid
Around the hilum of the lung
Sub-carinal
All the above
Although the most common location of the bronchogenic cyst is superficial midline supra-sternal, it can also be found sub-carinal in the mediastinum, around the hilum of the lungs and lateral to the thyroid gland.
Bronchogenic cyst aka non-communicating bronchopulmonary foregut malformation is a relatively rare hamartomatous lesion with prevalence of approximately 1/42,000 admissions.[] Although it is more commonly seen in pediatric population, it may be detected for the 1st time during adulthood without any sex predilection.
It usually originates as a late budding from the ventral side of embryonic lung or the tracheobronchial tree that occurs between the 26th and the 40th day of gestation. This abnormal bud then becomes a fluid-filled and blind-ending pouch termed bronchogenic cyst. Most of them are asymptomatic at birth and early life. Later in life, it may be symptomatic due to cyst enlargement leading to local compression and pressure on adjacent tissue/organ, occasionally secondary to infection or perforation.[]