Polymorphous low-grade adenocarcinoma (PLGA) is a minor salivary gland neoplasm that primarily occurs in intraoral sites. An extraoral location of the tumor is rare, with nasal cavity tumors representing <1% of PLGAs [1]. The tumor generally involves the palate but has been reported to occur in the base of the tongue, upper lip, buccal mucosa, tonsils, and retromolar pad [2]. PLGA usually occurs in the fifth and sixth decades of life with a female/male ratio of 2:1 [3,4].

To date, only six cases of PLGA presenting as a nasopharyngeal mass have been reported; none have been reported in Korea [5-10]. Nasopharyngeal PLGA grows slowly, painlessly, and has few symptoms, including unilateral ear fullness and nasal obstruction. Here, we describe a case of nasopharyngeal PLGA including clinical characteristics, pathology, treatment, and prognosis, along with a review of the literature.

A 51-year-old male patient presented with right-side ear fullness without nasal symptoms. No neck mass was noted. He did not smoke or drink alcohol and had no past history of acute disease, with the exception of cataract surgery. Nasal endoscopy revealed an irregularly shaped mass on the right salpingopalatine fold (Fig. 1). Paranasal sinus CT showed a 20×23×30-mm polypoid mass in the lateral wall of the right nasopharynx without surrounding bony destruction or intraorbital or skull base invasion (Fig. 2). A right middle ear effusion was observed on otoscopy. Punch biopsy of the nasopharyngeal mass was performed in the outpatient department. Pathology revealed a benign salivary gland tumor consistent with pleomorphic adenoma (Fig. 3).

The tumor was resected using an endoscopic approach, without further evaluation because the preoperative biopsy result was definitively benign [11]. Under general anesthesia, the transnasal endoscopic approach was used with 0- and 30-degree 4-mm nasal endoscopes (Karl Storz SE & Co. KG, Tuttlingen, Germany). The posterior portion of the right inferior turbinate was excised to create a working space for the endoscope and to expose the tumor. A circular incision of the mucosa was then made around the mass using a sickle knife, and further dissection was performed using a Freer elevator. The right pterygoid bone was exposed after the tumor was excised with a 2-mm resection margin. Frozen biopsy specimens revealed a carcinoma of undetermined type. Frozen sections prepared from the intraoperative margin tissue revealed a negative resection margin. The gross surgical specimen showed a pale brown to tan soft tissue mass measuring 20×13×10 mm; it was reduced in size compared to the preoperative CT, due to the outpatient punch biopsy. Finally, a fibrin-collagen patch (TachoComb^®; Nycomed, Linz, Austria) was applied to the wound site, followed by Merocel^® (Medtronic, Jacksonville, FL, USA) packing from the right posterior nasal cavity to the nasopharyngeal cavity. The Merocel was removed 2 days post-surgery; the patient was discharged from the hospital on the following day without significant complications. The final diagnosis was PLGA with the resection margin free of tumor (Figs. 4-6). A PET-CT scan confirmed no remnant nasopharyngeal mass or neck metastasis. Follow-up PET-CT performed at 7 months after nasal endoscopic surgery revealed no abnormal lesion suggestive of recurrence. The right middle ear effusion subsequently improved and is undergoing follow-up monitoring. At the 24-month follow-up, the patient showed no signs of local recurrence or distant metastasis (Fig. 7).

Histologically, PLGA is characterized by its morphologic variability, cytologic blandness, and an infiltrative growth pattern [5]. In most instances, the tumors are grossly circumscribed; however, they are unencapsulated and invade adjacent tissues microscopically. Neurotropism is a frequent finding. The growth pattern varies and includes solid islands, tubules, trabeculae, cribriform nests, cysts, and papillae. The lesions that most frequently cause diagnostic difficulties with PLGA are pleomorphic adenoma and adenoid cystic carcinoma [5]. PLGA is locally infiltrative, often with prominent perivascular and perineural invasion. These features can help to differentiate this tumor from both pleomorphic and monomorphic adenomas; usually, well-circumscribed tumors lack the infiltrative nature of PLGA. Differential diagnosis of PLGA from adenoid cystic carcinoma is difficult. Many of the histologic features of these two entities (solid and cribriform patterns and neurotropism) are similar; histologic distinction is virtually impossible. Immunohistochemical findings can distinguish the two lesions; PLGA exhibits positive EMA, S-100, and CEA findings.

Clinically, PLGA has a low tendency for aggressive behavior; thus, the recommended treatment is surgical excision, and the results are generally excellent. No cases of lymphatic spread have been described; therefore, neck dissection is unnecessary unless there is clinical evidence of lymph node involvement. If the tumor has not been completely resected, adjuvant radiotherapy should be performed to prevent tumor recurrence [6]. PLGA rarely occurs in the nasopharynx, and there is no definite treatment of choice. En-bloc mass excision using the transpalatal or nasal endoscopic approaches are options; however, the transpalatal approach may cause several complications, including pain, bleeding, and oronasal fistulas. Exclusive endoscopic resection can avoid potential complications and shorten the hospital stay.

To date, six cases of nasopharynx PLGAs have been reported. Lengyel, et al. [7] reported a case with skull base invasion and intracranial spread confirmed by CT. Radiotherapy was performed. Follow-up CT scans revealed a partial response to radiotherapy, and the patient was still living at 51 months postradiotherapy. Wenig, et al. [5] reported a patient with PLGA who underwent transpalatal tumor resection and exhibited uneventful recovery at 9 months after the operation. Furthermore, four previous studies found that patients with PLGA who underwent exclusive transnasal endoscopic tumor resection recovered fully without additional treatment [6,8-10]. Our case is the fifth report of a patient with nasopharyngeal PLGA who underwent nasal endoscopic tumor resection without additional therapy. Our findings, together with those of previous studies, suggest that the simple endoscopic approach is a feasible treatment for nasopharyngeal PLGA. However, during endoscopic surgery, the surgeon must be able to resect the mass with adequate safety margins to ensure they are free of tumor (e.g., by identifying negative margins in frozen biopsy). When the tumor extends beyond the nasopharynx or endoscopic view, we suggest that open surgery (e.g., transpalatal approach) should be used, rather than the endoscopic approach. In addition, open surgery should be performed when local recurrence is detected after endoscopic surgery.

In patients with nasopharyngeal PLGA limited to the nasopharyngeal mucosa, the endoscopic approach is feasible if the surgeon is able to resect the PLGA with sufficient margins. This procedure is curative, can reduce the length of the operation, decrease the incidence of wound-related complications, and shorten the hospital stay.