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November 1996, Volume 46, Issue 11

Case Reports

Parotid Gland Lipoma - A Rare Entity

Suhail Muzaffar  ( Department of Pathology, Aga Khan University Hospital, Karachi. )
Naila Kayani  ( Departments of Pathology, Aga Khan University Hospital, Karachi. )
Sheema H.Hasan  ( Departments of Pathology, Aga Khan University Hospital, Karachi. )

Introduction

Although lipoma is commonly found in soft tissues, the parotid gland lipoma is among the rarest benign primaiy tumors of the major salivary glands. The unilateral swelling of the parotid gland is not an uncommon clinical problem, however, lipoma as a cause of parotid gland enlargement seldom comes in mind as differential diagnosis. We have discussed the clinic pathological features of parotid gland lipoma with special emphasis on possible preoperative diag­nosis of this lesion.

Case Report

A 32 year old woman presented with painless mass growing gradually in the left parotid region for the past four years. She did not seek medical advice earlier as the mass was asymptomatic. Physical examination revealed a soft, lobu­lated, painless mobile mass occupying the left parotid region. The cervical lymph nodes were not palpable and there was no evidence of facial nerve involvement. A preoperative clinical diagnosis of pleomorphic adenoma was made. The patient underwent the superficial parotidectomy and the lesion was completely resected with surrounding normal parotid gland.
The resected specimen received as an outside referral case consisted of large, lobulated fragment of parotid gland tissue measuring 8x6x5.5 cms. Sectioning of specimen revealed a yellow, thinly encapsulated mass of 5 cms and surrounded by compressed salivar gland tissue (Figure 1).

Histological examination revealed well encapsulated mass of mature lipocytes arranged in lobular pattern with intervening tumor was surrounded by compressed normal salivary gland (Figure 2).

Discussion

Lipomas are the most common neoplasms of mesenchy­mal origin. These are benign, encapsulated fatty tumors which may arise in any location where fat is normally present. The majority are subcutaneous and generally found on extremities, trunk and neck regions. The lipomas of the deep tissue are rare and often detected at a relatively later stage of development. These have been described in various sites including anterior mediastinum, chest wall, retroperitoncurn, paratesticular re­gion and intraosseaus etc. The parotid swelling, whether unilateral orbilateral is not an uncommon clinical presentation seen in patients of all ages. Many neoplastic and non-neopias­tic causes of parotid gland enlargement have been described1. The majority of the parotid gland tumors are benign and largely represented by the benign mixed tumors2. The lipoma of the salivary glands is rarely seen and the majority are described in the parotid gland region3 and only few cases are reported in the literature4-8. Occasional cases of hibernoma and lipoblastoma in an infant have also been reported in the parotid gland region9,10. Being a rare neoplasm, the diagnosis of lipoma is seldom suspected on clinical examination. There is no reliable method of establishing a preoperative diagnosis of lipoma of salivary glands. The imaging studies including ultrasonography and computed tomography have not proven valuable for establishing the diagnosis. Tumors of the parotid gland can be delineated accurately with CT scan, however; it cannot accurately differentiate between benign and malignant parotid neoplasms. The features which favour a malignant parotid lesion on CT scan are ill-defined margins, local invasion, diffuse spread throughout the gland and enlarged regional lymph nodes. However, some of these features have also been seen in benign ns11,12.  The extensive use of fine needle aspiration cytology is an important diagnostic technique in readily accessible parotid gland lesions13. The diagnosis of a lipomatous lesion can be made reliable by this technique if one keeps in mind the possibility of lipoma in differential diagnosis of parotid gland swelling. As a conclusion1 this lesion should be included as a rare possibility in the differential diagnosis of tumors involv­ing the parotid gland.

Acknowledgement

We are grateful to Mr. Muhammad Azim for his assistance.

References

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9. Cathoun, K H., Clark, W LI and Jones, J.D Parotid lipoblastoma in an infant Otorhinolaryngol., 1987;14:41-44
10. Vinayak, BC. and Reddy, K.T N. Hibernoma in the parotid region. J. Laryngol. Otol., 1993;107 257-258.
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12. Van-Mieghem, F, Corthouts, B., Degryce, H. et al. Computed tomography of major salivary gland tumors A retrospective study of 31 eases. J Beldg Radiol, 1971:74 193-199.
13. Roland, N.J., Caalin, A.W., Smith, PA. et at. Fine needle aspiration cytology of salivary gland lesions reported immediately in a head and neck clinic I. Laryngol. Otol., 1993;107:1025-1028.

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