Discussion
Lipomatous tumors comprise 0.5% of salivary gland tumors, with the most common site being the parotid, followed by the submandibular gland.1 Histologically its spectrum can range from pure lipomatous neoplasm like the one seen in the cutaneous site or can be admixed with epithelial component specific to salivary gland.3
Thus, it can be of monophasic (only lipomatous component) or biphasic (epithelial plus lipomatous component) histological type. Among the biphasic type, the epithelial component can be of oncocytic or non-oncocytic.1 Oncocytic adenolipoma is an extremely rare benign tumor of salivary glands which consists of oncocytic epithelial components admixed with mature adipocytes in varying proportion.4 When Chi et al. reported in 2015, only 18 such cases were reported in the literature.5 This rare condition has been published mainly as single case presentation in the literature under different names as oncocytic sialipoma, oncocytic lipoadenoma, and adenolipoma.3
Most of the cases in the literature revealed that the oncocytic adenolipoma presented as a slowly growing, asymptomatic swelling most commonly from the parotid gland. The other areas where adenolipoma can be found include breast, thyroid, parathyroid, and skin.6 The duration of symptoms ranged from 15 days to 11 years.7 However, in our case, the history of onset was more than 18 years. Such a long duration has not been reported before. The age of onset for the condition has been widely reported from 7 to 89 years old, but mostly seen in adults with a mean age of 57.7 years old.8 There are literature stating equal sex predilection to being slight male predominance of 2-4:1.3 The treatment usually consists of excision with no risk of recurrence or aggressive behavior .8
The pathogenesis of the lesion is still elusive. There are different speculations regarding it. One theory given by Nagao stated it as an entrapment of glandular component during lipomatous proliferation. He suggested it being not of neoplastic origin but as a type of lipoma rather than hamartomatous origin.9 However, Parente et al. found the disorganized proliferation of neural and vascular structures by which they gave a theory of hamartomatous origin.10 The hypothesis of the hamartomatous nature given by Parente et al. was negated by Akrish et al., who proposed another theory. Their theory suggested that it was the dysfunction of the salivary gland, leading to a modification of the normal gland function that leads to the tumor. To support this theory were the reasons as prolonged history, lack of recurrence after excision, and histological features as ductal ectasia, periductal fibrosis, oncocytic metaplasia and replacement of glandular tissue with mature adipocytes and chronic inflammatory cells.11
Clinically, the differential diagnosis of the present case with a huge lesion might include varieties of the neck mass, including all benign lesions of the salivary gland. Radiological investigation of CT scan helped us to narrow down the differential to the fat-containing lesion as lipoma to lipoadenoma. Except for the huge size of the mass, the radiologically, the lesion was not that suggestive of being malignant type. However, FNA cytology was not found to be helpful for us. Histologically, the differential diagnosis of oncocytic adenolipoma includes all other lesions containing oncocytes, such as oncocytoma, oncocytic carcinoma, Warthin’s tumor, and oncocytic cystadenoma, as well as oncocytic variants of pleomorphic adenoma, myoepthelioma, mucoepidermoid carcinoma, and epithelial-myoepithelial carcinoma.6,8 The excisional surgery was done as reported in almost all cases reported in the literature.1,2,5,7 We followed the patient for five years, and until now, no recurrence of the lesion was noted. The present case is reported with the aim to make aware of the rare possibility of this extremely rare lipomatous lesion of the salivary gland in a patient presenting with a huge neck mass. We also aimed to confirm the long-term disease-free interval of 5 years after the surgical resection in this lesion.