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Neuroradiology Case of the Week

Case 61

Karin Westesson and P-L Westesson MD, PhD, DDS

Clinical Presentation: A 13-year-old female presented with a parotid mass. MRI of the face was requested for evaluation.

Radiological Findings: There was a large mass lesion in the tail region of the right parotid gland in its superficial portion. It measured 2.5 cm by 2.5 cm by 5 cm. The lesion had multiple septations and was mostly cystic in character. There was no enhancement.

Diagnosis: Low grade acinic cell carcinoma

Discussion:  Acinic cell carcinomas are slow-growing, low-grade malignant salivary gland neoplasms that account for 17% of all salivary malignancies and 30% of all primary parotid malignancies [2]. Most arise in the parotid gland, however they may also originate in the major and minor salivary glands, upper lip, buccal mucosa, and the palate, but rarely in the parapharyngeal space and sublingual gland [4]. All ages are affected, but the majority of patients are females ages 38 to 46. Interestingly, this is a decade younger than most other parotid malignancies [1,2]. Patients present with a rock-hard mass which is associated with pain and itching over the course of the facial nerve. In 8% of cases, there is facial nerve paralysis involving a combination of cranial nerve VII and V3 neuropathy [1). The exact cause of these carcinomas is unknown, but it is a combination of environmental and genetic factors. Possible factors also include previous radiation exposure specifically for thyroid disease, family history, and chronic inhalation of wood dust [3,4]
    Pathologically, acinic cell carcinomas appear as a well-circumscribed, tan-grey rubbery mass which may be cystic and multinodular if a recurrent tumor. They grow in solid sheets of basophilic serous cells. These cells are responsible for the tumor’s prominent cytoplasmic basophilia and contain zymogen granules, which are the secretory product of acinar cells [2]. Although they appear benign, they are microscopically infiltrative [3]. Imaging of acinic cell carcinomas is non-specific and they appear as pleomorphic adenomas [2].
    The differential diagnosis include pleomorphic adenoma, which is by far the most common mass lesion in the parotid gland, other primary parotid gland tumors such as adenoid cystic carcinoma, squamous cell carcinoma and epidermoid carcinoma.
    The goal of primary treatment is to surgically excise the tumors with negative margins but this is linked with a lower chance of survival [4]. A superficial lobectomy is adequate for the majority of benign parotid tumors and associated with good clinical outcome [2]. If the tumor is large and deep into the neck or if it is multinodular, it will reduce the survival rate [2]. Recently, fast neuron beam radiation has been a successful alternative to surgery [4]. The 5 year survival rate is 82% and the 15 year rate is 68% [3]. Recurrence is common and it requires rigorous surgical reexcision [2].

References:

1. Harnsberger HR. Handbook of Head and Neck Imaging. St. Louis: Mosby, 1995.
2. Som PD, Brandwein MS. “Salivary Gland: Anatomy and Pathology.” Head and Neck Imaging, 4th Ed. Eds. Peter M. Som and Hugh D. Curtain. St. Louis: Mosby, 2003.
3. Valvassori GE, Mafee MF, Carter BL. Imaging of the Head and Neck. Stuttgart: Georg Thieme Verlag, 1995.
4. http://www.aciniccell.org - updated 21 July 2003. Accessed 5 August 2003.