Dermoid Cyst: Imaging Features

Dermoid cysts (or mature cystic teratomas) are benign germ cell tumors composed of mature epithelial elements (skin, hair, desquamated epithelium, and teeth). They account for 95% of all ovarian germ cell tumors and 15% - 20% of ovarian neoplasm. Patient presents with non specific abdominal, pelvic pain, bladder, GI complaints and symptoms of menstrual abnormalities. They have wider age distribution, but most commonly occur in age group (16-55). Ultrasound (US) is the initial imaging investigation of choice, transabdominal or transvaginal.
Dermoid cysts are highly variable ranging from a predominantly solid to cystic appearing mass. On US, they are smooth-walled cystic structure with varying internal composition depending upon mixture of epithelial elements and extent. Pure sebum is anechoic; bone, teeth, calcification are hyperechoic with dirty distal shadowing; hair floating above sebum gives ‘tip of iceberg’ appearance; multiple linear echogenic interface within cyst refer to as ‘dermoid mesh’ while fat mixed with sebum is hyperechoic resembling a solid lesion. On CT, well defined cystic appearance with fat content and calcification (eg, tooth) is suggestive of a dermoid. MRI reveals high signal on T1-weighted and intermediate to high signal intensity on T2-weighted images, but are not specific. The loss of high signal intensity on fat suppressed T1-weighted sequence however confirms the fat content of a dermoid. Endometrioma due to its hemorrhagic products may resemble dermoid on T1 and T2-weighted images. However, characteristic shading (signal loss) on T2- weighted MRI is diagnostic of endometrioma. Worrisome features for malignant transformation includes large size (>10cm), mural enhancing nodule within a tumor. Torsion is the most common complication while rupture, malignant degeneration, infection are uncommon. Keeping in mind these complications, dermoid cysts are often resected while small (less than 6 cm) tumors needs non surgical management and follow up.
The main objective of an imaging study is to adequately evaluate adnexal mass for a better treatment. The management plan differs for benign or malignant diagnosis. Adnexal mass posses a real challenge. US is the initial imaging study for patients with suspected adnexal mass. MRI is an excellent tool to assess and characterize these masses especially when they are indeterminate on US as in our case. Lesion size, location, complex morphology are some of the contributing factor for a mass to be indeterminate.