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Sebaceous lymphadenoma is an unusual salivary gland neoplasm which is rarely correctly diagnosed pre-operatively in the parotid gland. Two cases of sebaceous lymphadenoma are presented in which, in common with most cases reported in the literature, the correct pre-operative diagnosis was not made. Sebaceous lymphadenoma rarely transforms into a malignant tumour. Fine needle aspiration cytology identifies a benign process in the majority of patients who receive appropriate treatment on this basis. Although an uncommon tumour, it should be taken into consideration in the differential diagnosis of a solitary parotid mass.
Sebaceous differentiation in salivary glands was first described by Hamperl 1 in 1931 and has been reported in 11 to 28% of normal parotid glands 2 3 and in 6% of normal submandibular glands 2. Neoplasms of sebaceous derivation, in the major salivary glands, are rare and include sebaceous lymph-adenoma, sebaceous carcinoma, sebaceous adenoma and sebaceous lymph-adeno-carcinoma.
Sebaceous lymph-adenoma is a rare, benign tumour of the parotid gland 4–15. It is characterized histologically by islands of epithelium showing sebaceous differentiation distributed in hyperplastic lymphoid tissue. This tumour must be differentiated from more common benign tumours, although this may be difficult based on fine needle aspiration cytology (FNAC). Two cases of sebaceous lymph-adenoma are described, in which, as with most cases reported in the literature, the correct pre-operative diagnosis was not made.
A 72-year-old male presented with a 4-week history of a painless swelling in the right upper neck. Physical examination showed a 2.5 x 1.5 cm firm, non-tender mass in the lower pole of the right parotid gland which was confirmed by ultrasound (US). There was no facial paralysis. FNAC revealed a few lymphocytes, foamy macrophages and an occasional cluster of oncocytic epithelial cells. No fibrillary or myxoid material was present. Appearances were suggestive of Warthin’s tumour. Right superficial parotidectomy was performed without complications and there was no recurrence at 16 months follow-up.
The gross specimen showed a 1.8 x 1.1 cm solid, lobulated tumour with a nodular cream-coloured cut surface (Fig. (Fig.1).1). Microscopically, the tumour was well circumscribed, composed of cords and islands of epithelium with sebaceous differentiation, associated with lymphoid tissue including germinal centres (Fig. (Fig.2).2). The features were those of a benign sebaceous lymph-adenoma.
This 57-year-old male presented with a 4-week history of a painless swelling in the left upper neck. Physical examination revealed a 2 x 2 cm firm mass in the tail of the left parotid gland which was confirmed by US. FNAC was inconclusive, but, on clinical and radiological grounds, the most likely diagnosis was thought to be pleomorphic adenoma. A left superficial parotidectomy was performed without complications and there was no recurrence of the tumour at 12 months follow-up.
Macroscopic examination revealed a well-circumscribed tumour measuring 3.5 x 2.5 cm with surrounding fibro-fatty tissue. Microscopy revealed lymphoid tissue with solid and cystic components containing variably sized islands of benign basaloid epithelium showing sebaceous differentiation. The lymphoid tissue showed focal hyperplasia. Cystic spaces were lined by multilayered epithelium including sebaceous and squamous cells. A diagnosis of benign sebaceous lymphadenoma was made.
Sebaceous lymphadenoma is a rare benign tumour which is histologically characterized by islands of epithelium showing sebaceous differentiation distributed in hyperplastic lymphoid tissue. Rawson and Horn 16 first described this benign neoplasm in 1950 and the name “sebaceous lymph-adenoma” was given by McGavran et al. in 1960 17. The majority of these lesions occur in the parotid glands or periparotid lymph nodes 18.
Sebaceous lymphadenoma of the parotid gland typically presents as a painless mass in patients over 50 years of age. Although it is known to occur equally in both sexes 10 12 both of our cases were male. Published case reports of sebaceous lymphadenoma do not often give a pre-operative diagnosis. In those cases where a pre-operative diagnosis was made on clinical, radiological or cytological grounds, they are found to be varied (Table (TableII).
Sebaceous lymphadenoma was not correctly identified by pre-operative investigations in the majority of cases. Boyle and Meschter 12, in a single case report, suggested that the FNAC findings in a sebaceous lymphadenoma were distinctive and accurately reflected the histological morphology, although the lesion is so rare that the diagnosis may be easily overlooked. In both of our cases, the FNAC reached did not indicate the correct diagnosis.
Two cases in the literature were diagnosed pre-operatively as pleomorphic adenoma 11 14, the most common benign neoplasm of the parotid gland. The clinical presentation of sebaceous lymphadenoma is similar to that of pleomorphic adenoma i.e., a painless parotid swelling with no facial nerve involvement. In the Shukla and Panicker case 14, the true diagnosis was sebaceous lymphadenoma plus concomitant squamous cell carcinoma. One of our cases was thought pre-operatively to be a Warthin’s tumour (adenolymphoma), which is the second most common benign parotid neoplasm, again with similar clinical features. Failure to make a correct pre-operative diagnosis of sebaceous lymph-adenoma did not alter the surgical management of these patients as non-urgent surgical excision is required for all these tumours. Malignancy was suspected in two cases. In the Assor case 5, the pre-operative FNAC suggested mucoepidermoid carcinoma. In the Mayorga et al. case 9, the sebaceous lymphadenoma was concomitant although the FNAC correctly diagnosed acinic cell adenocarcinoma.
On rare occasions, sebaceous lymphadenoma can transform into sebaceous lymph-adeno-carcinoma. This is an extremely rare malignant neoplasm and only four cases have been reported 19. Synchronous occurrences of a sebaceous lymphadenoma with another neoplasm such as Warthin’s tumour 8 13, acinic cell carcinoma 9 and squamous cell carcinoma 14 in the same parotid gland have been reported, but they are also rare.
FNAC is a useful technique in evaluating salivary gland lesions pre-operatively. Cytological diagnosis of a benign neoplasm by FNAC has been found to correlate with histological diagnosis of a benign neoplasm following excision in 83% of cases 20. Failure to do so may be due to a variety of factors including operator inexperience, sampling error and inadequate samples. In both of our cases, FNAC correctly diagnosed benign tumours. However, when interpreting FNAC from parotid gland masses, these limitations of the procedure should be considered.
Sebaceous lymphadenoma is an unusual salivary gland neoplasm which is rarely correctly diagnosed pre-operatively in the parotid gland. Transformation into a malignant tumour is rare. FNAC identifies a benign process in the majority of patients who receive appropriate treatment on this basis. Although an uncommon tumour, it should be considered in the differential diagnosis of a solitary parotid mass.