Lip pleomorphic adenomas: case series and literature review

Abstract

Background: Pleomorphic adenoma (PA) is the most frequent benign salivary gland tumor, but a lip PA is rare. Although this tumor may be definitively diagnosed by imaging or a tissue biopsy if it is reasonably large, PAs on the lip are relatively small, and they present findings that are similar to those of other lip lesions, which can make a preoperative diagnosis difficult.

Methods: We analyzed all PAs in the oral region and lesions on the lips treated in our department over the past 20 years, and we discuss them together with the relevant literature.

Results: We found that 11.8% (n=6) of the PAs occurred on a lip (upper lip: 9.8%, lower lip: 2.0%), and ~1% of all mass lesions of the lips were PAs. The average size of the lip PAs was 1.5±0.7 cm (range, 0.7-2.2 cm). For preoperative diagnostic assistance, ultrasonography (US) (n=4), magnetic resonance (MR) (n=3), or no imaging (n=2) was used. An excisional biopsy was performed in all cases, and to date, no recurrence or malignant transformation has been observed.

Conclusions: Lip PA is relatively rare. Because almost all of these lesions are small, a preoperative diagnosis is more difficult compared to palatal lesions. This tumor is also prone to long-term neglect and has the potential for recurrence and malignant transformation. It is thus necessary to perform an excision that includes the capsule and surrounding tissues, and careful postoperative follow-up should be continued.

Keywords: Pleomorphic adenoma (PA); case series; lower lip; minor salivary gland tumor; upper lip.

Figure 1

Clinical and histological findings of Patient 1. (A) Extra-oral findings at the first physical examination. Localized swelling above the upper lip on the right side (arrowhead). (B) Intra-oral findings at the first physical examination. A spherical mass with a smooth surface was recognized inside the right upper lip. (C) Intraoperative photograph at the excisional biopsy. (D) Macroscopic image of the resected specimen. A mass with a capsule measuring 5×7 mm. (E-G) H&E staining showing histopathologic images of the resected specimen. Both epithelial cells and myoepithelial cells were observed in the tumor area. The epithelial cells formed ductal structures, and myoepithelial cells were observed surrounding the outside of the duct. There were two layers of epithelium and myoepithelium, with myoepithelial cells proliferating to migrate into the stroma (arrowheads). (E) Gross image. The tumor was well encapsulated. Scale bar: 1 mm. (F) Low-power magnification. Scale bar: 200 µm. (G) High-power magnification. Scale bar: 50 µm. The images are published with the patient’s consent.

Figure 2

Imaging and histological findings of Patient 2. (A) Axial T1-weighted MR image showing the mass with mid-level signal intensity (arrowheads). (B) Sagittal STIR MR image showing the mass with low-to-high signal intensity (arrow). (C) US showing the circular mass with no internal blood flow. (D-F) H&E staining showing histopathologic images of the resected specimen. Both epithelial cells and myoepithelial cells were observed in the tumor area, and they had a bilayer structure. Fibrous stroma was found. Some of the epithelial cells had squamous metaplasia (arrowhead). (D) Gross image. Scale bar: 1 mm. (E) Low-power magnification. Scale bar: 200 µm. (F) High-power magnification. Scale bar: 50 µm. MR, magnetic resonance; STIR, short T1 inversion recovery; US, ultrasonography.

Figure 3

Clinical, histological, and imaging findings of Patient 3. (A) Intra-oral findings at the first physical examination. A mass with irregularities and a smooth surface was recognized inside the left lower lip. Axial (B) and coronal (C) STIR MR images showing the mass with high signal intensity (arrowheads and arrow). (D) US showing a well-defined but partly lobulated mass with poor internal blood flow. (E) Macroscopic image of the resected specimen. (F-H) H&E staining showing histopathologic images of the resected specimen. Both epithelial cells and myoepithelial cells were observed in the tumor area, and they had a bilayer structure. Plasmacytoid cells were observed (arrowheads). (F) Gross image. The surgical margin was unclear. Scale bar: 1 mm. (G) Low-power magnification. Scale bar: 200 µm. (H) High-power magnification. Scale bar: 50 µm. (I) Intra-oral findings at a follow-up after the tumor resection. There were no signs of recurrence, and good healing progress was observed. The images are published with the patient’s consent. STIR, short T1 inversion recovery; MR, magnetic resonance; US, ultrasonography.

Figure 4

Proportion of lip PAs encountered in our department. (A) Pie chart of all PA cases by site. The number next to the site’s name = the number of cases. (B) Pie chart of all mass lesions in lips by disease. The number next to the disease’s name = the number of cases. PA, pleiomorphic adenoma; SCC, squamous cell carcinoma.