A rare case of parotid gland lipoma arising from the deep lobe of the parotid gland.

Lipomas are the most commonly encountered benign mesenchymal tumors, but their occurrence in the head and neck is rare, even more at the level of the parotid region where they can be found nearby the parotid capsule, inside the capsule, or within the gland. In addition, lipomas involving the deep parotid lobe are extremely unusual. That is why lipomas are not often considered for differential diagnosis of parotid lumps. Concerning diagnostic tools, magnetic resonance imaging (MRI) is nowadays considered as the main imaging examination for parotid lipomas due to a characteristic signal intensity on T1- and T2-weighted images. Furthermore, even if the cost of MRI is nearly three times that of computed tomography, MRI is accurate, safe, and has few biological costs for the patient. In this reported case, MRI provided all information for either diagnosis or preoperative planning being the best diagnostic tool regarding tumor margin characteristics and surrounding tissues' involvement. Concerning treatment, surgical excision of parotid masses is always mandatory for definitive diagnosis, but it is challenging because of the facial nerve. For this reason, a well-established surgical technique is mandatory for success. The authors present a rare case of parotid gland lipoma arising from the deep lobe and discuss diagnostic tools and surgical technique.

INTRODUCTION

Lipomas are the most commonly encountered benign mesenchymal tumors, arising in any location where fat is normally present. Their occurrence in the head and neck is rare, even more at the level of the parotid region where they may occur adjacent to the parotid capsule, inside the capsule, or within the substance of the gland.[123] Moreover, lipomas involving the deep parotid lobe are extremely unusual and are not often considered in differential diagnosis. Occasionally, an intracapsular lipoma may be associated with intracapsular degeneration of the gland.[2] Concerning the age of onset, lipomas are most common from the fifth to the sixth decades of life. Males are 10 times more affected than females.[4] Surgical excision of these tumors is always necessary for definitive diagnosis,[5] but it is challenging because of the facial nerve which courses throughout the parotid gland and could be damaged during surgery if not performed traditionally and by experienced hands. For this reason, a well-established surgical technique is mandatory for success. The authors present a rare case of parotid gland lipoma arising from deep lobe and discuss diagnostic tools and surgical technique.

CASE REPORT

A 66-year-old female came to our observation with a huge, painless swelling of the left parotid region claiming surgical excision because of cosmetic discomfort. Moreover, she complained about the slow growing of the lump over the years. Clinical examination showed a soft, nontender, mobile mass which is deep into the superficial skin surface lump measuring 6 cm × 4 cm in size. The swelling was located over the region of the left parotid gland. The overlying skin was normal without any sign of adhesion. The examination of either the neck or the facial nerve function was unremarkable [Figure 1]. The MRI of the parotid region showed a well-defined mass with adipose tissue signal arising from the left deep lobe of the parotid gland extending through the superficial tissues [Figure 2]. Fine-needle aspiration cytology (FNAC) was not performed due to the enough amount of information provided by MRI. Thus, a parotidectomy was planned. A classic parotidectomy incision was performed and through blunt dissection, the main trunk of the facial nerve was identified at the stylomastoid foramen. From the facial nerve, its main trunks were separated from the overlying superficial parotid lobe until a yellowish fatty well-encapsulated mass was identified at the deep lobe [Figure 3]. The tumor was then totally enucleated after mobilization of the overlying facial nerve branches. The histopathological examination confirmed the presence of a lipoma. Postoperative recovery was uneventful, and the facial nerve function was normal at discharge. Neither recurrence nor Frey's syndrome was observed 2 years after the surgery [Figure 4].

Figure 1

Patient's preoperative frontal view. Huge swelling of the left parotid region

Figure 2

Preoperative T1-weighted magnetic resonance imaging

Figure 3

Intraoperative view: The fatty yellowish mass comes out from the surrounding parotid tissue after blunt dissection

Figure 4

Facial nerve function of the patient after surgery is normal

DISCUSSION

Lipomas are the most common benign mesenchymal encapsulated tumors histologically similar to mature adipose tissue. Only an average of 25% of lipomas and their variants are observed in the head and neck region.[6] More rarely, they can arise from the parotid gland. The reported incidence varies from 0.6% to 4.4% among parotid tumors. Concerning the age of onset, they arise most frequently in the fifth and sixth decades of life with male predominance.[7] Lipomas of the deep parotid lobe are even more infrequent. They use to grow slowly, usually without symptoms. In most cases, like ours, patients claim surgery for cosmetic concerns.[8] Deep lobe parotid lipomas may extend between the sternocleidomastoid and digastric muscles, causing an asymptomatic parotid region soft swelling. In other cases, they may extend to the parapharyngeal space, causing medial displacement of the lateral pharyngeal wall;[9] facial nerve involvement[10] and pain[7] are uncommon and have been rarely described. Clinical examination is insufficient in all cases to identify the nature and location of deep parotid lipomas. Hence, imaging examination such as magnetic resonance imaging (MRI) may be helpful in either diagnosis or surgical planning.[11] Even if the cost of MRI is nearly three times that of computed tomography (CT), we believe that MRI is the main imaging examination for parotid lipomas due to a characteristic signal intensity on T1- and T2-weighted images. In fact, lipomas show high T1 and low T2 signal characteristics of fatty tissue that is comparable to subcutaneous fat. The fat-suppression sequence of lipomatous lesions demonstrated on MRI clearly distinguish these masses from other types of tumors, provide superior soft-tissue definition, and accurately reveal the location of the tumor in relation to the facial nerve. Furthermore, MRI is safe and has few biological costs for the patient.[101112] Fine-needle aspiration biopsy (FNAB) still has a significant false-negative rate in salivary gland tumors and seems to be unreliable in diagnosing parotid lipomas. Besides, fibrosis or adhesion between the facial nerve branches and the lipoma capsule following FNAB may occur.[13] In a recent study, diagnostic challenges of parotid lipomas were deeply analyzed. The authors compared MRI, CT, and FNAC findings in a small group of patients with parotid lipomas, concluding that CT and/or MRI are more reliable and accurate than FNAC (100% vs. 25% of specificity). In fact, the rarity of these lesions and the yield of a mixture of mature tissue and normal salivary gland elements might result in false negatives of “no pathologic changes” or even in “insufficient material” specimens. Moreover, fat cells from lipomas would be identical to normal subcutaneous fat.[14] In the present case, MRI resulted in a well-defined homogeneous mass, and fat-suppressed sequences were conclusively helpful in distinguishing the lipoma from other tumors and lipid masses. Moreover, MRI provided adequate information for preoperative planning. For this reason, in this reported case, the authors did not perform FNAC. Surgical intervention in these tumors is challenging. Possible postoperative morbidities, such as facial nerve dysfunction, Frey's syndrome, facial scar, or asymmetry contour, may occur and have to be explained to the patient. Transient or temporal facial nerve dysfunction may be encountered after surgery in the case of deep lobe parotid lipoma, thus full exposure of the facial nerve and also facial monitoring are pivotal.[8] In this case, we performed traditional superficial parotidectomy exposing all the branches of the facial nerve from the main trunk by blunt dissection. We found that the procedure reduced recurrence rate and the incidence of postoperative Frey's syndrome. In conclusion, lipomas involving the deep parotid lobe are extremely rare. Concerning diagnosis, MRI is the best tool for either diagnosis or surgical planning compared to other investigations such as CT and FNAC. Surgical management of deep lobe lipomas is challenging and should be performed by experienced surgeons due to the risk of a facial nerve lesion. Formal superficial parotidectomy and blunt dissection of facial nerve trunks are mandatory in all cases, and postoperative functional and esthetic results should be the major concerns.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

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Conflicts of interest

There are no conflicts of interest.