Mature teratoma is the most common GCT, as it represents 95% of GCTs and 30% of ovarian tumors, making it the most common ovarian neoplasm in children and teenagers [1, 2]. Although common in children and young adults, ovarian teratoma can occur at any age . It is commonly unilateral but can be bilateral in 9.52%  and 10.5% of cases . Ovarian torsion is the most frequently encountered complication; however, most patients are asymptomatic [3, 4, 7]. Other less frequent complications include infection and rupture . Ultrasound is considered one of the most supportive investigation tools as it is safe and readily applied, especially when the patient presents with an acute abdomen, as in our case .
Teratoma is classified into mature and immature teratoma . Immature teratoma is defined as having immature elements from any of the three germ layers, commonly with neural origin, but for grading, only the neuroectodermal tissue is considered [5, 10]. Immature teratoma is the most common malignant ovarian germ cell tumor (MOGCT), and its histological grading plays an integral role in the management and prognosis of the patient. Therefore, extensive sampling of the solid areas in teratoma specimens is crucial, which could reveal another germ cell tumor or an immature component [11, 12]. In the presented case, after sampling the specimen thoroughly, only mature tissue elements composed of skin and adnexa, well-differentiated cerebellum, respiratory epithelium, and glial tissue were seen. No evidence of immature elements or mixed germ cell tumor components were identified. Thus, the diagnosis of mature cystic teratoma was established.
Another point to mention is that malignant transformation (MT) is rare in MCT at a rate of 1–2% , and various malignancies have been reported in teratomas, with squamous cell carcinoma (SCC) being the most common [13, 14]. However, other reported malignancies include apocrine adenocarcinoma  and carcinosarcoma . Treatment of MCT is by surgical removal of the cyst by laparoscopy, with laparotomy reserved for large-sized tumors, as in our case [17, 18]. Recurrence rate after removal is about 4% .
As mentioned above, mature cystic ovarian teratoma (MCT) can have different histological elements [5, 6]; however, the finding of a well-differentiated cerebellum is extremely rare. The first case reported of a well-differentiated cerebellum within mature teratoma was by Askanazy in 1907 . Furthermore, to the best of our knowledge after an extensive literature review, only 22 cases have been reported [19,20,21,22]. The cerebellum formed within ovarian teratoma usually has a less organized morphology , and it can be associated with different morphological features such as dendritic abnormalities of Purkinje cells  or presence of Obersteiner external granular layer .
Well-differentiated cerebellum within ovarian teratoma represents a diagnostic challenge to the pathologist as it shares many similarities with the immature elements in teratoma , which has a different prognosis and management modalities depending on the grade and stage . This dilemma can be resolved by identifying that the cerebellar tissue in mature teratoma has more of an organoid architecture versus the haphazardly arranged immature tissue elements seen in immature teratoma [20, 22]. However, this is more elusive and difficult to assess, especially in frozen section/intraoperative consultation, where the external or internal granular layer of the cerebellum can be difficult to differentiate from immature neural tissue [20, 22]
Interestingly, ovarian teratoma with both well-differentiated cerebellum and immature components occurring together has also been reported . So, finding one does not exclude the other. Hereby, we emphasize the importance of extensive sampling of ovarian teratoma and attention to such rare findings.