Lipoma of the parotid gland arising from the deep lobe: two cases report

¹Department of Pathology, Hassan II University Hospital, Fez, Morocco, ²Department of Otorhinolaryngology, Hassan II University Hospital, Fez, Morocco, ³Department of Radiology, Hassan II University Hospital, Fez, Morocco, ⁴Biomedical and Translational Research Laboratory, Fez, Morocco

^&Corresponding author
Asmae Mazti, Department of Pathology, Hassan II University Hospital, Fez, Morocco

Introduction    

Lipomas are the most common neoplasms of mesenchymal origin, arising in any location where fat is normally present. However, the literature on head and neck lipomas is limited and has primarily been in the form of separate case reports [1]. Only about 13 per cent of lipomas occur in the head and neck region, most commonly in the posterior neck [2]. Rarely, lipomas can occur in the anterior neck, infratemporal fossa, oral cavity, pharynx, larynx and parotid gland [3]. This later location is extremely rare. Lipomas usually occur sporadically, but rarely they can be associated with several inherited disorders, including hereditary multiple lipomatosis, Gardner´s syndrome and Madelung´s disease [4]. Lipomas of the parotid glandare relatively rare and comprising only 0.6-4.4% of reported benign parotid neoplasms [5]. In a Turkish study analyzing 165 cases of parotid gland tumors, the lipomas represented 3% [6]. In this paper, we present two new cases of a parotid gland lipoma and we discuss its clinical, pathological and therapeutic characteristics.

Patient and observation     

Case 1: this patient is a 68-year-old man, without medical history, who was presented with a left parotid tumefaction, gradually increasing in volume. The clinical examination revealed a left parotid tumefaction, which is soft, painless, without facial paralysis or lymphadenopathy. A magnetic resonance imaging (MRI) showed a hypersignal-T1 hypersignal-T2 mass (Figure 1), which disappeared after the suppression of the fat signal (Figure 2). An exofacial parotidectomy was performed. On macroscopic examination, it was a yellowish mass, well circumscribed and homogenous (Figure 3). Histological examination revealed a parotid gland with an adipose proliferation arranged in lobules. It was compound of mature adipocytes, without atypia, lipoblasts or necrosis (Figure 4, Figure 5).

Case 2: a 61-year-old diabetic woman presented with a 6 months history of dysphagia, odynophagia with a tumefaction in the right parotid region. The clinical examination revealed a soft, well-defined and mobile tumefaction, bulging on the right half of the oropharynx with normal mucosa. A CT-scan was performed. It showed a lipomatous mass in the right region of parotid with extension to the later opharyngeal area. A magnetic resonance imaging (MRI) was performed in addition. It revealed an lipomatous mass measuring 8.8cm in diameter, with a mass-effect on the sub-maxillary artery. A parotidectomy was performed. The macroscopic examination showed a yellowish well-defined and homogenous mass, arising in the parotid tissue. The microscopic examination revealed a parotid gland with an adipose proliferation arranged in lobules. It was compound of mature adipocytes, without atypia, lipoblasts or necrosis (Figure 6).

Discussion     

Lipomas are the most common benign mesenchymal tumors. They tend to appear on the shoulders, chest, trunk, neck, thighs and armpits. Lipomas of the parotid gland are extremely rare and usually are not included in the differential diagnosis of parotid masses. Clinically, they may be frequently confused with Warthin´s tumor, pleomorphic adenoma, parotid cys and benign mesenchymal neoplasmssuch as haemangioma and lymphangioma [7]. From the few studies reporting lipomas in the parotid gland, the incidence is about 0.6 to 4.4% [3]. Lipomas of the parotid region can be classified into periparotidlipomas (those tumours that are found to be compressing the lateral surface of the parotid gland) and intraparotidlipomas (tumours that are totally surrounded by salivary tissue) [8]. Our cases were an intraparotidlipomas. Concerning the age, they arise most frequently in the fifth and sixth decades of life with male predominance [9], which is in accordance with our case. The main reported causes for this benign entity are: history of trauma, positive family history of lipomas, obesity, previous head/neck irradiation, corticosteroid therapy [10].

Typically, lipoma is a relatively asymptomatic mass which appears as a slow-growing, painless and mobile mass in the parotid region with normal overlying skin [10]. Imaging modalities (ultrasound scan and MRI scan) can give a high accuracy in the preoperative diagnosis [11], giving valuable information for the malignant potential of the lesion and the exact location, which helps for the surgical strategy. The MRI is capable of higher resolution in soft tissues [1]. Like adipose tissue, lipoma produces strong signals on T1- and T2-weighted MR images and a weak signal on fat suppressed images, which is indicative of lipomatous tissue. Moreover, the margin of a lipoma is clearly defined by MRI as a "black rim" enabling to distinguish lipomas from the surrounding adipose tissue, a distinction that cannot be made with CT images [12].

Fine needle aspiration (FNA) is not useful for parotid gland lipomas, giving insufficient answers and should be avoided [13]. Similarly, Layfield et al. [14] found that FNA did not provide sufficient information to make a diagnosis in four out of nine benign fatty tumours of the parotid gland. Histologically, lipoma consists of circumscribed mass of mature adipose tissue, with a thin fibrous capsule at the periphery, differentiating them from simple aggregations of adipose tissue [15]. Surgical excision is the mainstay of treatment. This surgical management of lipoma in the parotidgland is controversial. Some surgeons recommend superficial parotidectomy, while others advocate simple enucleation [16]. The recurrence rate of parotid lipomas after surgery is estimated at 5% [15].

Conclusion     

Lipomas of the parotid are rare. Magnetic resonance imaging remains the most relevant radiological examination, which allows through a multiplanar evaluation and a spatial resolution to characterize a parotid lesion and define its localization. However, the diagnosis remains histological.

Competing interests     

The authors declare no competing interests.

Authors' contributions     

All the authors have read and agreed to the final manuscript.

Figures     

Figure 1: case 1: MRI of the lipoma of the parotid gland: a hypersignal-T1 hypersignal-T2 mass

Figure 2: case 1: disappearance of the signal on fat-suppressed image

Figure 3: case 1: a yellowish, well-defined mass in the parotid tissue

Figure 4: case 1: adipose proliferation limited by a fibrous capsule (H&E x100)

Figure 5: case 1: the adipocytes are regular, without atypia ou lipoblasts (H&E x400)

Figure 6: case 2: a proliferation of regular adipocytes, without atypia ou lipoblasts (H&E x400)

References