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.