Teaching Case

A 50 year old woman was followed for an adenoid cystic carcinoma treated 12 years before in the left maxillary sinus

A fifty year old woman was followed for an adenoid cystic carcinoma which developed 12 years before in the left maxillary sinus for which she was treated by chemotherapy and surgery (resection of the left maxilla). Seven years later she presented a first relapse which was treated surgically. Four years later a second relapse, revealed by a local mass and pain, was controlled by radiation therapy. Three months after the end of treatment the patient presented an exquisite pain located immediately under the left orbit. The pain severely increased with pressure on a specific trigger zone. The patient was referred to MR to rule out a new local relapse.

Perineural spread, a characteristic feature of adenoid cystic carcinoma, and a frequent finding in squamous cell carcinoma, is one the most insidious way of tumor spread and a decisive impact on the therapeutic option. In many institutions, lesions reaching the skull base are not considered as surgically resectable and are treated with palliative radiation therapy. On a prognostic standpoint, perineural spread often have tumor recurrence and poor long-term survival (1). Cranial nerve V and VII are particularly at risk in case of facial area and parotid tumors respectively. Spread can occur both in an anterograde and retrograde ways. “Skip” lesions can be seen and justify the need to cover the entire course of both nerves when performing imaging. MR is able to demonstrate perineural invasion in 30% to more than 50% of patients which are asymptomatic (1-2). Gadolinium-MR makes the diagnosis by showing enlargement and abnormal contrast enhancement, which cannot be depicted with CT (2-3). Since physiological uptake can be seen in portions of the facial nerve, only the enlargement of the nerve should be considered as a reliable sign of nerve invasion. Gadolinium MR has been shown to have a sensitivity of 95%, although it may fail to depict microscopic foci of perineural tumor infiltration (2). The use of high spatial resolution images (3 mm or less slice thickness and 512 x 512 matrix) is recommended. Fat saturated T1 weighted scans may improved the detection of subtle areas of contrast technique. However, this technique may be degraded by susceptibility artifacts at the air/soft tissue interface, a frequent situation in the skull base (2).