Objective: To study the endoscopic anatomy of the 4th ventricle and lateral brainstem regions via the midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach assisted by a neuronavigation system and discuss the feasibility and indications of this approach. Materials and Methods: Craniotomy procedures performed via the midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach were simulated on 8 adult cadaveric heads fixed by formalin, and the related anatomic structures in the 4th ventricles or around the brainstem were observed through the 08 endoscope or alternatively 308 one. A neuronavigation system was used to measure the exposed area of the floor of 4th ventricle, the maximum exposure range, the length of the floor of 4th ventricle, the shortest distance from the midpoint of posterior arch of atlas to the opening of the aqueduct in the 4th ventricle and to the jugular foramen on both sides, respectively. Results: All the anatomic structures within the 4th ventricle and partial anatomic landmarks around brainstem were identified by means of the midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach. The exposed area of the floor of 4th ventricle is 459.68 +/- 73.71 mm(2). However, the total exposed area is 1601.70 +/- 200.76 mm(2). The length of the floor of 4th ventricle is 36.08 +/- 2.63 mm. The shortest distance from the midpoint of posterior arch of atlas to the opening of the aqueduct in the 4th ventricle is 63.87 +/- 2.97 mm, to the jugular foramen on both sides, respectively, is 40.11 +/- 2.47 mm/40.30 +/- 2.31 mm. Conclusions: Midline suboccipital endoscopic transcerebellomedullary fissure keyhole approach can basically meet the medial and lateral route of the transcerebellomedullary fissure approach. A tumor within the 4th ventricle or near the jugular tubercle extending into the 4th ventricle through the cerebellomedullary fissure can be removed by this approach.