Parapharyngeal pleomorphic adenoma - a rare but typical lesion.

Clinical History

This is a case of a 66 year old man with a mass in the left parapharyngeal space, which had been growing for over 25 years.

Imaging Findings

A 66 year old man complained of a soaring pain in the back of his throat. He reported that a benign mass had been found in his throat on a CT 25 years ago. He had been having a foreign body sensation ever since, but the pain used to be tolerable. We performed contrast-enhanced MSCT (Fig 1) and MRI (Fig 2,3) of the head and neck and found a submucous, smoothly margined 4 cm lesion in the left parapharyngeal space which extended between the deep lobe of the left parotid gland and the left palatal tonsil. Compared with the old records (images were not available anymore), the diameter of the lesion had increased by more than 1 cm. The attending ENT surgeon of a nearby university clinic, to whom the images were presented, proposed to resect the tumour without prior biopsy. At the time of this case report, the patient was still unsure whether to follow this advice. However, he was instructed that although there was not the merest hint on the present imaging studies, malignant transformation may occur in this tumour type, and that increasing pain may be an ominous sign.

Discussion

Masses in the parapharyngeal space account for only 0.5% of all head-neck neoplasms [1]. Almost 50% are derived from the salivary glands [2]. These are typically located in the prestyloid compartment. Most exhibit a connection with the deep lobe of the parotid gland (Fig 2a), but some may originate from minor salivary glands. Pleomorphic adenoma (PMA) is the most common neoplasm in the parapharyngeal space [3]. It is also the most common solid tumour of the salivary glands, irrespective of dignity. PMAs of the parotid are either found incidentally or may cause pain and swelling. Tumours in the deep compartments are usually larger at the time of diagnosis. In cases with deep tissue extension, MRI and/or CT are mandatory. In recent years, the cross-sectional imaging characteristics of PMA have been exhaustively described.
On MR images, a well-defined margin or a lobulate border, an inhomogeneous aspect, high tissue contrast, intermediate or high signal intensities and an either inhomogeneous or peripheral enhancement were observed. MRI was superior to CT in detecting a pseudocapsule [4]. MR findings of a complete capsule, lobulated contour or high T2 signal intensity have a high predictive value for the correct diagnosis [5]. Overall diagnostic accuracy of MRI is specified as about 83% [6]. Calcification, as in the present case, seems to be rather unusual [7].
Most tumours in the parapharyngeal space are benign. However, malignancy accounts for up to 30% in this region and even long-standing benign PMAs may eventually de-differentiate. Therefore, surgical treatment is usually advised and can be done with few complications. Preoperative imaging will guide the surgeon to choose the best approach.

Two similar cases have already been published on Eurorad by Hermans and by Meingan and co-workers in 2001. Here, we wanted to stress the typical MR imaging characteristics of this tumour type, which in conjunction with its anatomic features almost make it an Aunt Minnie diagnosis.

Differential Diagnosis List

Final Diagnosis

Submucous parapharyngeal pleomorphic adenoma.

URL:	https://www.eurorad.org/case/7748
DOI:	10.1594/EURORAD/CASE.7748
ISSN:	1563-4086