Aim Dermoid tumors are uncommon intracranial tumors that grow slowly and typically manifest in individuals aged between their third and fifth decade. Dermoid cyst is an uncommon ectoderm originated benign cyst. Giant dermoid cysts are more rare, especially in the posterior fossa. Although intracranial dermoid cyst may commonly occur in the cerebellopontine angle and chiasma opticum, it can bedetected in cerebral hemispheres as well as intraventricular area. Here, we present a case involving a fourteen years old congenitaly deaf and mute patient with edited operation video.

Material and Method The patient was fourteen years old and was deaf and mute from birth. There were complaints of headache, vomiting, and imbalance that gradually increased in recent months. In the MR imaging examination;A calcified, cystic mass measuring 5.2 x 4.8 x 3.8 cm, compressing the brainstem and the 4th ventricle, was revealed in the posterior fossa (figure 1A–M).

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Abstract OP-055 Figure 1

Preoperative, intraoperative and postoperative images (figure 1). A- Preop Axial MRI B, C- Preop Coronal MRI D-Preop Sagittal MRI E- Preoperative Diffusion MRI F- Intraop Figure G-Intraop Figure (strand of hair) H- Intraop Figure (Tumor Mass) I- Intraop Figure (Total excision of the mass) H- Postop CT K- Postop Sagittal MRI L- Postop Axial MRI M- Postop Coronal MRI.

Results When the patient‘s MRI examinations are examined;The temporal horn of the ventricle became prominent and hydrocephalus began. The patient underwent surgery in the prone position and total mass resection surgery was performed with posterior fossa craniotomy. There were also strands of hair in the mass. In many surgeries, mass excision surgery is performed after ventriculo-peritoneal shunt or external ventricular drainage. In our case, emergency mass removal surgery was successfully performed without the need for these different surgeries, and it was observed that the hydrocephalus disappeared in the postoperative period. The histopathological diagnosis of the patient was defined as dermoid cyst.

Conclusions Posterior fossa tumors are generally primary in the pediatric age group, unlike adults, and metastasis is not observed. In adults, posterior fossa tumors are considered metastases until proven otherwise. Dermoid tumors are very rare. The mass pressing on vital organs(Pons, mesencephalon) and causing hydrocephalus by obstructing the 4th ventricle requires urgent removal of the mass. In our case, although there was the beginning of hydrocephalus, the mass was completely removed and hydrocephalus was prevented without the need for ventriculoperitoneal shunt placement.