Findings: Axial CT without contrast (due to acute renal failure) demonstrates 6 cm x 8cm hypodensity in the pelvis (7cm high - from bottom of sacrum to mid-femoral head). The mass contains a rim of calcification along its left anterior wall. The rectosigmoid and rectum walls are also thickened.
Diagnosis: Dermoid cyst or benign cystic teratoma.
Discussion: Dermoid cysts are benign germ cell tumors that affect females of any age, but occur most frequently in patients that are between the ages of 10 and 30 years old. They are the most common ovarian neoplasm, accounting for 10-25% of ovarian tumors, and are bilateral in 15-25% of the cases. They consist of mature ectodermal components including bone, teeth, and hair.
A dermoid cyst can present as an abdominal or pelvic mass, but is more often detected radiographically. CT characteristically shows a complex-appearing cystic mass with a smooth, well-defined surface and a focus of calcification, usually resembling a tooth. The sebaceous contents are the same attenuation as fat. On ultrasound, fluid-fluid levels representing a hairball are common, and the "tip of the iceberg" sign shows an "echogenic mass that fades into acoustic shadowing due to sound absorption." Plain films confirm calcification in the mass.
Despite their benign nature, dermoid cysts are usually surgically removed, because torsion, perforation, infection, and rarely, rupture and chemical peritonitis complicate them. Malignant transformation, generally into invasive squamous cell carcinoma, occurs in 1-2% of the cases. It begins as Rokitansky's protuberance, a partially-solid nipple-like nodule that penetrates the capsule of the tumor. Progressive growth leads to invasion into the bladder, bowel, or pelvic wall, and sometimes, distant metastases.
References:
Brant WE and Helms CA. Fundamentals of Diagnostic Radiology. 2nd ed.
Lippincott, Williams & Wilkins, Philadelphia; 1999:822, 865-66.
Kido A, Togashi , Konishi I, Kataoka ML, Koyama T, Ueda H, Fujii S, and Konishi J.
Dermoid cysts of the ovary with malignant transformation: MR appearance. AJR 172(2):445-9, 1999.
Occhipinti KA, Frankel SD, and Hricak H. The ovary. Computed tomography and magnetic
resonance imaging. Radiol Clin North Am 31(5):1115-32, 1993.
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