Signs in Imaging

APPEARANCE Please refer to Dr Proto's From the Editor article (p 2) in the January 1998 issue for instructions regarding submission of manuscripts for Signs in Imaging. In particular, note that prospective authors are requested to write to the Editor for approval of the sign to be submitted, to avoid duplicate preparation of the same sign. The " Tip of the Iceberg " Sign1 The " tip of the iceberg " sign refers to the ultrasonographic (US) appearance of a mass with an amorphous, poorly defined echogenic focus in the near field that causes posterior shadowing and thus obscures the posterior portion of the lesion and any structures behind it (1). Because these masses are frequently large, the tip of the iceberg sign is readily identified on both transabdominal and transvaginal US scans (Figure). EXPLANATION (a) Tip of the iceberg sign seen on an endovagi-nal US scan obtained with a 5.0-MHz transducer. There is a 3.6-cm echogenic left adnexal mass (cursors) with posterior acoustic shadowing. The multitude of interfaces formed by the mixture of hair and sebum in the near field produces the echogenic focus that hides the posterior wall of the cyst and thereby obscures the true size of the lesion. (b) A longitudinal transabdominal US scan shows the " tip of the iceberg " appearance of a large dermoid cyst (arrows). U = uterus. computed tomographic (CT) findings reveals that the fatty liquid detected at CT is usually hypoechoic or anechoic, but the fat intermixed with the hair strands is echogenic and often attenuates the ultrasound beam (2). In addition, in vitro scans of surgical specimens have proved that the strongly reflective echo pattern is caused by the multiple tissue interfaces of the hair and sebum within the cystic mass. Acoustic shadowing may totally obscure the back wall of a large, clinically palpable mass; hence, the term " tip of the iceberg " sign. DISCUSSION The echogenic focus at US appears as a solid mass but is actually a cyst that contains a mixture of fatty liquid (ie, sebum), matted hair, and cellular debris. It is the multiple tissue interfaces within this mixture that are responsible for producing the characteristic acoustic shadowing. The tip of the iceberg sign is the specific US appearance of a dermoid cyst. Dermoid cysts, also known as benign cystic teratomas, are benign germ cell tumors that are usually discovered in young women of …