This case nicely demonstrates the Rokitansky nodule (dermoid plug) seen within a Mature cystic ovarian teratoma.

Mature cystic teratomas of the ovary (dermoid cyst) are formed of well-differentiated components of two or more of the germ cell layers (ectoderm, mesoderm, endoderm). They are the most common surgically resected ovarian neoplasm and the most common ovarian tumor in children. 

They are usually asymptomatic. However, they can present with nonspecific abdominal pain. They are bilateral in around 10% of cases.

These lesions have variable appearances on ultrasound, depending on the overall internal constituents. They are easily diagnosed on CT and MRI, since these modalities are more sensitive to fat.

Mature cystic teratomas can be complicated by ovarian torsion (most common complication) if large in size. A far less common complication is rupture with secondary granulomatous peritonitis in less than 1% of patients.

Malignant transformation into squamous cell carcinoma is rare, occurring in 1-2% of cases.