Incidental finding of synchronous pleomorphic salivary adenoma and Warthin’s tumour within a parotid gland

Abstract

The presence of two histologically distinct lesions within the same salivary gland is rare. The majority of lesions detected in salivary glands are benign and unifocal. Ultrasound scans and MRI imaging may not detect separate lesions that are in close proximity and this presents a challenge for radiologists and surgeons in the diagnosis of salivary gland lesions. We present a case when incidentally two distinct lesions were discovered during extracapsular dissection of a suspected pleomorphic salivary adenoma. We aim to highlight the difficulty in diagnosing these rare entities using existing investigative techniques.

Background

Pleomorphic salivary adenomas (PSAs) are the most common type of neoplasm found in salivary glands accounting for 71% of benign lesions.¹ Warthin’s tumours are the second most common lesion which accounts for 22% of benign salivary gland tumours.¹ Despite being a benign lesion, a small number of long-standing PSAs can turn malignant. Literature has reported that there is a 3.3% risk of malignant transformation in recurrent PSAs.² Most benign tumours of salivary glands are asymptomatic and appear within a single gland having a single histological appearance. Warthin’s tumours can occur bilaterally in 6.5% of cases.³

This case report presents a 61-year-old man who had simultaneous PSA and Warthin’s tumour in close proximity within the same gland. Despite having multiple investigations prior to surgery, the distinction between the lesions was not detected. This raises an important consideration when diagnosing salivary gland lesions.

Case presentation

A 61-year-old man was referred to the oral and maxillofacial department at Pinderfields hospital with regards to sore gums when brushing his teeth and white patches on his buccal gingiva in all four quadrants of his mouth. Medically he was generally fit and well. His medications included atorvastatin and citalopram. He consumed 20–30 units of alcohol a week and occasionally smoked cigars. Smoking is a known risk factor for Warthin’s tumours and oral cancer.⁴

Incidentally during an extraoral examination a preauricular lump was noted on the right side of his face overlying the parotid region. On further questioning, the patient stated that he had been aware of the lump for over 25 years. The lesion was asymptomatic, mobile to palpation and non-tender. Normal facial nerve function was noted. To help establish a diagnosis, an ultrasound and fine needle aspiration (FNA) was requested. An FNA was used in our case as the patient was not keen to pursue surgical intervention. The cytology result was to inform the patient if the lesion was benign with no potential for malignant change, for example a Warthin’s tumour.

Investigations

The ultrasound scan showed in the superficial portion of the right parotid gland there was a well-defined lesion with a solid, non-vascular component and a well-defined cystic component measuring 20x7 mm. It was provisionally diagnosed as a benign salivary gland tumour most likely a PSA. The cytology collected contained branching epithelial groups and myxoid stroma fragments in keeping with the initial radiological impression of a PSA.

An MRI scan was later requested to aid with surgical planning for removal of the lesion. The scan showed the presence of a bilobed mass showing low signal intensity on T1 weighting and high signal intensity on T2 weighting which was again consistent with the provisional diagnosis of a PSA. This was located in the superficial part of the right parotid salivary gland and was positioned superiorly and anteriorly (figures 1–2).

Figure 1.

Axial section of MRI neck scan.

Figure 2.

Coronal section of MRI neck scan.

Differential diagnosis

Initial diagnoses included benign lesions such as a PSA or a Warthin’s tumour based on the history and clinical examination of the lesion. The ultrasound scan later noted a cystic component to the tumour. This meant malignant lesions including mucoepidermoid carcinoma, adenoid cystic carcinoma or acinic cell carcinoma could not be fully excluded until histological assessment of the tumour. The subsequent cytology result indicated a provisional diagnosis of PSA which was consistent with the benign features of the lesion on MRI.

Treatment

The provisional diagnosis was explained to the patient including the small risk of a long-standing PSA turning malignant. Surgical options to remove the lesion using an extracapsular dissection (ECD) approach plus the possible requirement for a conventional parotidectomy technique were discussed. The potential risks including damage to the facial nerve, development of a sialocele, recurrence of the lesion and Frey’s syndrome were explained. The decision was then made to remove the lesion.

The lesion was accessed using a ‘mini’ modified Blair incision under general anaesthetic. A cruciate incision was made in the superficial muscular aponeurotic system/parotid capsule and this was reflected as one layer to allow for primary closure after removal of the lump. A nerve monitor was used throughout the procedure to reduce the chance of facial nerve injury. At the time of surgery, it was noticed that the lesion had a pale, granular area with a separate region which was dark and cystic in nature. The lesion was removed and a vacuum drain was placed. The patient was discharged the following morning after drain removal.

Outcome and follow-up

A postoperative review 4 weeks after surgery showed the surgical wound to be healing well with no symptoms of a sialocele. On examination, there were no residual palpable lumps and there was normal motor and sensory function. The patient did not report any symptoms of gustatory sweating which would indicate Frey’s syndrome.

On histological examination, sections of the lesion showed parotid gland tissue containing groups of epithelial cells, some arranged in glandular structure and others spindled with surrounding myoepithelial cells. These were surrounded by a myxoid/chondroid stroma. Adjacent to this was a cyst which was lined by a dual layer of oncocytic cells. The cyst contained eosinophilic, proteinaceous material and was surrounded by occasional collections of lymphocytes. These appearances were consistent with a coexisting PSA and Warthin’s tumour (figures 3–4).

Figure 3.

Histopathology slide showing pleomorphic salivary adenoma.

Figure 4.

Histopathology slide showing Warthin’s tumour.

Discussion

Salivary gland neoplasms are relatively rare with a incidence of 1–2 per 100 000.⁵ Over 30 salivary gland tumours are listed in the WHO’s classification of salivary gland tumours.⁶ PSAs and Warthin’s tumours are the most common lesions found in salivary glands. Smoking has been reported as an important risk factor in the development of Warthin’s tumours.⁴ In reported cases of multiple synchronous lesions in a unilateral salivary gland, they are most commonly of the same histological type with Warthin’s tumours being of the highest incidence.⁷ Warthin’s tumours occur bilaterally in 6.5% of cases.³ Zeebregts et al reviewed 341 patients who underwent parotidectomy for removal of salivary lesions and discovered that 14 cases contained two or more tumours in the sample.⁷ Multiple Warthin’s tumours were the most common combination followed by PSA/Warthin’s tumour.

When reviewing multiple lesions of differing histology, it was discovered that the PSA/Warthin’s tumour combination had the highest incidence.⁸ Gnepp et al reviewed 680 patients with salivary gland tumours and discovered only one case of distinctly separate PSA/Warthin’s lesions within the same gland.⁹ Malignant lesions have also been discovered alongside benign lesions and it is important to be aware of this possibility.^{8 9}

Benign salivary gland lesions usually present as a lump or swelling overlying a salivary gland which are usually mobile, slow growing and soft to palpate. When differentiating between malignant and benign lesions, it is important to clinically assess facial nerve function for palsy which can indicate malignant invasion. Malignant lesions can ulcerate surrounding tissue and spread to surrounding lymph nodes.

Ultrasound scanning is the recommended first line image modality for small superficial lumps within a salivary gland.¹⁰ It allows for distinction between cystic and solid components with the ability to guide clinicians in collecting an aspirate of the tumour. The sensitivity for fine needle aspiration cytology of benign lesions has been quoted as 98% and 96% for malignant lesions. The specificity for benign lesions is 96% and 79% for malignant lesions.¹¹ In our case, an MRI was later requested to aid with the surgical planning for removal of the lesion. The use of MRI gives greater soft tissue differentiation than CT imaging.¹² The ability to accurately localise lesions within the gland provides a roadmap for surgeons and can differentiate malignant from benign lesions. Smaller lesions may not be detectable on MRI scanning. In our case, a single bilobed lesion was identified on the MRI scan but two distinct lesions were detected histologically. Similar cases of small Warthin’s tumours in close proximity to PSAs that could not be distinguished on MRI scanning have been reported.^{13 14}

In our case, an ECD technique was used as opposed to a superficial parotidectomy (SP). Over the past 10 years, a large number of oral and maxillofacial surgery (OMFS) units have changed their surgical practice with regards to removal of benign parotid lesions. There is an increasing trend for surgeons to prefer ECD due to the reduced morbidity and similar risk of recurrence in comparison with a SP.¹⁵ McGurk et al compared the outcome of malignant lesions that were clinically diagnosed as benign prior to surgical treatment and were removed by either ECD or SP.¹⁶ Their review showed there is no worse outcome for ECD patients in comparison with SP patients when treated for ‘simple’ (discrete, mobile, <4 cm in size) tumours. ECD has therefore been deemed to be a safe method of treatment for suspected benign salivary gland lesions. If a lesion is diagnosed intraoperatively as being deeper than expected or in closer proximity to the facial nerve then transition to a parotidectomy technique would need to be considered. The ability and requirement to transition between surgical techniques is an important factor to consider.¹⁷ Using ECD in our case allowed us to visually identify the two separate lesions intraoperatively.

Patient’s perspective.

The patient did not wish to add any information.

Learning points.

• It is important to consider a patient’s smoking history when diagnosing salivary gland lesions. This is due to a higher incidence of Warthin’s tumours in smokers.

• Simultaneous salivary gland lesions can occur within the same gland.

• Current imaging and diagnostic tests will not necessarily detect both lesions.

• Extracapsular dissection can allow for identification and safe removal of two separate parotid lesions within the same region.