Primary Cystic Pleuropulmonary Synovial Sarcoma Presenting as Recurrent Pneumothorax.

Primary pleuropulmonary synovial sarcomas are quite rare, representing 0.1-0.5% of all pulmonary malignancies. We report an entirely cystic monophasic synovial sarcoma in a 25-year-old male who presented with recurrent pneumothorax and no evidence of a mass lesion on imaging. The purpose of this case report is to increase awareness of neoplasms clinically presenting as a pneumothorax with no imagining evidence of a mass-forming lesion and emphasize the significance of fluorescent in situ hybridization testing in nontypical synovial sarcoma cases.

Introduction

Synovial sarcoma is a malignant mesenchymal neoplasm, which most commonly occurs near the joints of the extremities in young adults [1, 2]. However, primary pleuropulmonary synovial sarcoma (PPSS) is an extremely rare tumor [3], which occurs in a subset of conformed synovial sarcomas. Synovial sarcoma has a wide morphological spectrum and is classified into multiple subtypes including: monophasic epithelial, monophasic fibrous, biphasic, and poorly differentiated. Cytogenetic studies have demonstrated that synovial sarcomas have a consistent, specific chromosomal translocation t(X;18) (p11.2;q11.2) and the consequent fusion gene SYT-SSX [4, 5]. The transcriptional deregulation by this specific fused gene is thought to be associated with augmented tumorigenesis. In rare instances, synovial sarcomas can present in the pulmonary cavity, as pleuroplumonary synovial sarcomas [1, 3, 6]. We present a case of entirely cystic PPSS which presented as recurrent pneumothorax, confirmed by demonstration of pathognomonic t(X;18) translocation by fluorescent in situ hybridization (FISH) in surgically removed tissue.

Case Report

The patient was a previously healthy 25-year-old male who began having sharp, left-sided chest pain and shortness of breath shortly after he returned to his home town at an altitude of 7,000 feet from sea level.

Chest X-ray revealed a left-sided pneumothorax and a chest tube was placed. Following resolution of his pneumothorax, the chest tube was removed and the patient was discharged only to return the following day with similar symptoms. Chest X-ray showed recurrent left-sided pneumothorax with no evidence of any lesions (Fig. 1). Subsequent imaging showed left-sided lesion (Fig. 2). Video-assisted thoracic resection of a left lower lobe wedge was performed. Gross examination revealed a unilocular bleb measuring 1.1 cm in size with clear resection margins. Microscopically, the collapsed bleb had a spindle cell proliferation in the cystic (bleb) wall which was covered with single layer of reactive mesothelium (Fig. 3a). The spindle cells focally extended into the immediate underlying lung parenchyma (Fig. 3, inset). The lesional cells were hyperchromatic with high nuclear/cytoplasmic ratios and were arranged in orderly fascicles (Fig. 3b). There were 2 mitoses per 10 high-power fields and no tumor necrosis. Immunohistochemical stains were performed, which showed the spindle cells to be negative for cytokeratins (cytokeratin AE1/3, cytokeratin 7, cytokeratin 5/6), epithelial membrane antigen (EMA), and Wilms tumor protein 1 (WT1). The neoplastic cells showed weak staining with CD99 and BCL2. FISH for a SS18 (18q11.2) rearrangement showed a break apart consistent with a translocation involving the SS18 gene characteristic of synovial sarcoma (Fig. 4). Metastatic workup was negative. The patient received four cycles of doxorubicin/ifosfamide and is recurrence free 2 years after completion of chemotherapy.

Fig. 1

There is a pneumothorax on the left with approximately 3.8 cm of the distance between the pleural space apically. There is a mild mediastinal shift to the right. The right lung is clear. No pleural effusion, pulmonary edema, or focal consolidation is seen.

Fig. 2

A small opacity is present in relation to the inferior-lateral pleural surface and adjacent to the left hemidiaphragm, likely pleural thickening. Subcentimeter opacity is present in relation to surgical staples in the inferior left lung.

Fig. 3

Collapsed bleb (cyst wall) containing monotonous spindle-shaped cells with mesothelial cells on one side (a, b; HE, 4× and 20×). Spindle cells focally extended into the adjacent alveolar spaces without forming a nodular mass (Inset; HE, 4×).

Fig. 4

Dual-color, break-apart interphase fluorescent in situ hybridization for SS18 (18q11.2) gene rearrangement. Within a single nucleus, split red and green signal indicate the presence of a SS18 (18q11.2) rearrangement involving one chromosome, while a fused red-green signal within the same nucleus indicates an intact 18q11.2.

Discussion

We report a rare cause of recurrent spontaneous pneumothorax secondary to an entirely cystic pleuropulmonary synovial sarcoma. PPSS are rare, representing 0.1–0.5% of all pulmonary malignancies [1, 7]. These tumors may present with chest pain, cough, or hemothorax [7]. Entirely cystic/bullous PPSS presenting with recurrent pneumothorax have been rarely reported [1]. These lesions may be confused with benign cystic disease, type 1 pleuropulmonary blastoma, mesenchymal cystic hamartoma, lymphangioleiomyomatosis, and metastatic endometrial stromal sarcoma [3, 4, 8]. Before clinical FISH testing became readily available, many of the earlier cases with this histomorphology were likely reported as other entities such as mesenchymal cystic hamartoma [1, 3]. This patient's tumor was both cytokeratin and EMA negative, a very unusual immunohistochemical staining pattern seen in only 1 of 100 cases, highlighting the importance of ancillary FISH testing for the SS18 (18q11.2) rearrangement in this differential diagnosis [4, 5, 6]. Synovial sarcoma has a wide morphological spectrum, which is generally classified into multiple subtypes: monophasic epithelial, monophasic fibrous, biphasic, and poorly differentiated [2, 9]. Many clinical, microscopic and genetic parameters have been reported to influence the length of survival for synovial sarcoma [10, 11, 12]. The long duration of symptoms and initial slow growth of synovial sarcomas may simulate those of or give a false impression of a benign process [2, 12], such as in the case presented. Most primary pulmonary and mediastinal synovial sarcomas are located in the lung parenchyma, and rarely extend into the bronchial tree or occur in the heart or pericardium [13, 14]. Despite the rare occurrence of this tumor type, PPSS should be considered on the differentiation of a primary lung or pleura mass, especially in young and middle-aged adult patients [9]. Current treatment consists of surgical resection followed by chemotherapy, radiation therapy, or both [15]. This case report serves to increase awareness of neoplasms clinically presenting as a pneumothorax without evidence on imaging of lesion or mass and to emphasize the role of FISH testing in such cases as this of nontypical synovial sarcoma.

Statement of Ethics

The patient's informed consent was acquired prior to publication of the case.

Disclosure Statement

The authors have no disclosures to declare.