Teratomas account for 0.1–1.5% of all intracranial tumors and 2–4% of all intracranial tumors in children [3,7,9,20]. They usually occur near the midline and demonstrate two peaks by age distribution—during the neonatal/infancy period and between the age of 5–14 years [3,11,15]. They frequently occupy the pineal region (51%), followed by the sellar area (30%) [3]. The occurrence of posterior fossa teratomas in adulthood is extremely rare. Only several cases have been reported thus far in the literature [1,3-8,10,13,16,18-24]. The prognosis and clinical, histological, and radiographic features of posterior fossa teratomas are unknown. This study aimed to present our experience of posterior fossa mature teratoma in adults who underwent surgical resection at our institute. Furthermore, we performed a systematic literature review reporting all cases of posterior fossa mature teratoma that occurred in adulthood published thus far and described their peculiar features.

All procedures performed in studies involving human participants were in accordance with the ethical standards of the Institutional Research Committee (Asan Medical Center, reference No. 2020-1568) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

Fig. 1 shows a flow chart of the literature review process. A total of 502 articles were shortlisted in the search. An additional five related articles were identified through a search of the reference list of the identified articles. One hundred and two duplicate articles were removed. Review of the abstracts and titles led to the exclusion of 389 articles (353 unrelated topics, one review or meta-analysis, 20 pediatric cases, and 15 articles not written in English). Finally, 16 articles were deemed suitable for our literature analysis. We extracted the demographic features, clinical findings, and treatment outcomes from each study. We added two cases from our institute. In total, 18 cases were included in our study.

Germ cell tumors (GCTs) usually originate from the misplacement of embryonal tissues. GCTs comprise germinomas, teratomas, choriocarcinomas, embryonal carcinoma, and endodermal sinus tumor [11,12]. Teratomas account for 18% of all GCTs. Jennings et al. [11] have reported male predominance (52 : 18) in intracranial teratomas. In our study, the occurrence of posterior fossa teratomas was almost similar in both sexes. Maximal safe resection is curative for intracranial mature teratomas [2,9,12,17]. The effect of adjuvant chemotherapy or radiotherapy is controversial [14,17]. Most previous reports showed gross total or subtotal resection. Harada et al. [10] reported a fourth ventricle mature teratoma in a 62-year-old male patient. The patient underwent gross total resection, and the tumor did not recur for 4 years. The 10-year survival rates of patients with mature teratoma and malignant teratoma were 92.9% and 70.7%, respectively [16]. If gross total resection was not achieved, then the relapse rate was found to increase to 39% [3].

The occurrence of mature teratomas in the posterior fossa during adulthood is exceptionally rare. Our literature search only identified 16 previously reported cases. Posterior fossa teratomas located in the midline in approximately 72.2% patients, and they have various radiographic findings owing to its heterogeneous components [16]. Teratomas are misdiagnosed as low-grade tumors or other GCTs. In our case, a 50-year old man was followed up for 16 years. The initial diagnosis was pilocytic astrocytoma based on the findings of a posterior fossa cystic mass in young adults with focal nodular enhancement. However, after 16 years, the cystic mass increased in size, and the calcification became dense. They had common radiographic findings such as slow growing, mural node, and cystic mass. If surgical resection was not performed, then accurate diagnosis would not have been achieved. Bohara et al. [4] reported that a 41-year-old female patient had a posterior fossa mass suggestive of a dermoid cyst because the mass was hypodense on CT and involved the sinus tract in the occipital bone. Surgical resection was performed, and the pathologic confirmation was mature teratomas [4]. Coulibaly et al. [7] also reported a strong contrast-enhancing mass with dense calcification in the posterior fossa. It was diagnosed as meningioma preoperatively according to radiographic findings. A variety of radiographic features in teratomas due to heterogeneous components lead to misdiagnosis, followed by inappropriate treatment such as observation or radiotherapy. Due to the rarity of teratomas, it is difficult to consider teratomas in the initial differential diagnosis. In addition, Liu et al. [15] reported that seven of nine mature teratomas showed no contrast or mild contrast enhancement in the cyst wall, and the remaining two teratomas had moderate and heterogeneous enhancement in the solid portion. In contrast, malignant or immature teratomas showed intratumoral nodular enhancement. Additionally, they found that serum alpha-fetoprotein (AFP) levels were elevated in malignant teratomas, whereas the levels in mature teratomas were within the normal range [15]. Matsutani et al. [16] revealed that AFP or human choriogenic gonadotropin was not found in mature teratomas, whereas its level was elevated in immature or malignant teratomas. Kyritsis [12] also reported that carcinoembryonic antigen were positive in teratomas.

Spinal cord metastasis occurs in 10% of all intracranial GCTs. The incidence is higher for germinomas (10%), endodermal sinus tumors (23%), males (11%), and tumors in the pineal gland [11]. Goyal et al. [9] reported that 23 of 43 cases of central nervous system teratomas were located in the spinal cord. In our study, teratomas in the posterior fossa did not show cerebrospinal fluid seeding to the spinal cord.

The definitive diagnosis of intracranial teratoma can be made histologically. It is difficult to diagnose teratomas using radiological examination only. The heterogenous radiographic findings of intracranial teratoma often lead to misdiagnosis, such as lipoma, dermoid cysts, other GCTs, or craniopharyngiomas, especially in cases of suprasellar lesions. One of our cases was initially diagnosed as a low-grade glial tumor. Most previous cases showed various features and clinical findings. It is occasionally difficult to obtain tissue from tumors located in the posterior fossa because of its complex neurovascular anatomy (brainstem, cranial nerves, and critical vessels). However, whenever feasible, we should perform a craniotomy to ensure an appropriate diagnosis.

This study had several limitations. Because of its small number of patients, a statistical analysis was not performed. As a few cases were quoted from the papers written before 2000, it was difficult to obtain information about the patients or even the original articles.

The occurrence of mature teratomas located at the posterior fossa in adult patients are extremely rare. Only 16 cases have been reported thus far in the literature. Teratomas can show heterogeneous radiographic findings; hence, we should consider teratomas in the differential diagnosis. If it is possible, maximal safe resection and histological diagnosis are recommended.