Surgical management of the petrous teratoma

Teratomas are a subgroup of germ cell tumours. Intracranial teratomas are rare, comprising approximately 0.5% of all intracranial tumours, which commonly involve the middle-line structures of the cranium. According to the literature, however, petrous bone affected primarily is extremely rare. Decades ago, there were very few cases of patients who survived completely following surgical removal of intracranial teratomas with subsequent normal neurological development. Advances in neuroradiology and microsurgical technique now permit sooner diagnosis and successful treatment in many of these patients. A 4-year-old girl presented with a 3-week history of fever associated with headache and left-ear purulence, which had happened when the patient was 6 months old. Magnetic resonance imaging (MRI) demonstrated a large lesion of heterogeneous signal occupying the whole left middle fossa (Fig. 1). Computed tomography (CT) scan depicted that the left petrous bone was eroded (Fig. 2). The size of the mass was about 4 cm in diameter. The lesion was totally removed by an infratemporal epidural approach. Excision of the tumour was started from the centre of the lesion. The skull base was reconstructed with a temporalis fascia, which had harvested at the beginning of the case, draped over the floor of the middle cranial fossa. Without cerebrospinal fluid (CSF) leak, acoustic disorder or facial palsy, the post-operative course of the patient, was uneventful. The symptom of ear discharge gradually disappeared within a week. The post-operative MRI confirmed an en bloc resection of the tumour. Microscopic examination supported the intraoperative diagnosis of mature teratoma. For those petrous teratomas confined to the epidural space, a middle fossa craniotomy via an extradural subtemporal approach is the choice. To achieve enough operative space, the bone of the Kawase triangle, that is, delimited by the great superficial petrous nerve (GSPN) laterally, the porus trigeminus medially and the arcuate eminence at the base, can be drilled out firstly. To evade the important structures, there are three triangle-projections in the superficial petrous bone that should be localized before bone drilling: (1) the internal acoustic canal triangle, which is defined by the upper border of the meatus, the genu of petrous segment internal cartoid artery (ICA) and the intersection point of arcuate eminence and the drawn-out line of the GSPN; (2) the cochlear triangle, which is delineated by the meatus of the GSPN canal, the genu of petrous segment ICA and the intersection point of arcuate eminence and the drawn-out line of the GSPN; and (3) the petrous ICA triangle, which