CT rim effects in various head and neck lesions

The authors evaluated various head and neck lesions seen from April 1988 through March 1990 both by plain and enhanced CT, examined the incidence of rim effect (or rim enhancement), classified these effects, and discussed underlying mechanisms. The subjects were 177 patients with primary tumors (28 benign and 49 malignant tumors), lymphadenopathy associated with malignancy (9), inflammatory lesions (20), cystic lesions (12), other lesions (7), and 22 without abnormal findings. Among these 177, rim effects were observed in 22 cases (12%). These effects were analyzed and classified. The incidences of rim effect according lesion type are as follows; cervical lymphadenopathy associated with malignancy 5/9 (56%), primary tumors 8/77 (10%), inflammatory lesions none, cystic lesions 7/12 (58%), and others 3/7 (43%). The highest incidence was seen with cystic lesions including mucoceles of the paranasal sinuses and cervical cysts. Rim effects were classified as follows; Type 1: cystic pattern, Type 2: parenchymatous pattern, Type 3: vascular pattern and Type 4: others. Type 1 was seen in 15 cases (68%), Type 2 in 3 cases (14%), Type 3 in 3 cases (14%), and Type 4 in 1 case (5%). Type 1 included 6 cystic lesions, 3 malignant lymphadenopathies, 3 benign tumors and others. Type 2 included 2 malignant lymphadenopathies and 1 benign tumor, and Type 3, 2 jugular thromboses and 1 carotid atheroma. There was only one Type 4, a cystic lesion. Of interest is the mode of incidences among cervical lymphadenopathies associated with malignancy. Accessory chains showed rim effects in 3/7, all Type 1, and jugular chains in 2/13, all Type 2. The mechanism underlying the rim effects was discussed and the vascularity of the peripheral rims of the lesions appeared to be the most important factor in addition to technical artifacts inherent in CT. (author)