gms | German Medical Science

Objective: Petrosal approach is mandatory in the removal of petroclival tumors originating or locating anterior to the internal acoustic canal (IAC) - jugular foramen (JF) line. Such petroclival tumors have been removed, most popularly, by using the presigmoid petrosal approach. However, this approach must be criticized in several points; First, this approach is not physiologic in that the direction of approach is from posterior to anterior to the tumor passing through the cranial nerve fence and resulting in the high frequency rate of cranial nerve morbidity. Second, there is the danger of damaging vital temporal base draining veins including vein of Labbe. Third, no surgical options except cutting the tentorium are available in coping with the diverse extension of the tumors in horizontal and rostrocaudal direction. The authors developed TED scale to overcome the drawbacks of the conventional way of petrosectomy for the petroclival tumors.

Method: 35 cases of tailored petrosal approach were performed for the petroclival tumors during the most recent 3 years. The tumors were 13 petroclival meningiomas, 7 trigeminal schwannomas, 5 brainstem gliomas, 4 giant acoustic neuromas, 4 chondrosarcomas, 1 chordoma and 1 cases of AT/RT. In traditional concept of petrosal approach, design of petrosectomy starts from posterior part of the petrous bone to anterior part. However, we tailored extent of petrosectomy from anterior part to posterior part which is more physiologic. The extent of tailoring of petrosectomy, extension of each tailored petrosectomy and dural incisions according to the tumor extension at the sphenopetroclival area were carefully reevaluated. The tailoring (T) was scaled as full (f), medium (m), and small (s). The small tailoring is petrosectomy from under the V ganglion to the superior semicircular canal, medium is to the posterior semicircular canal and the full tailoring is to the jugular bulb. The extension (E) of each tailored petrosectomy was scaled as none (n), transcrusal (c) and translabyrinthine (l). The scaling of dural incision (D) was subtentorial (s) or transtentorial (t). This TED scale was matched with the tumor extension at the sphenopetroclival area. The area is divided as I, II, and III in horizontal dimension and A, B, and C in rostrocaudal dimension. Area I is lateral to the IAC-JF line, area II is from IAC-JF line to the midline, and area III is over midline. Area A in rostrocaudal dimension is from the jugular tubercle (JT) line to the level of porous trigeminus, area B is from the trigeminal porous to the pituitary stalk, and area C is over pituitary stalk to the subchiasmatic cistern. Whichever of the tailoring, the mandatory options of performing the petrosectomy is to include the dural boundary to the inferior petrosal sinus, exposure of the dura between the labyrinth and the superior petrosal sinus and opening of the Meckel's cave and porous trigeminus.

Results: Matching the TED scale and the tumor compartment at the sphenopetroclival area were suggesting the most appropriate approach for each tumor. Tumor extension from the JT line to the area IIB needed TfEnDt or TfEcDt. TfElDt was an another option if hearing was unserviceable. The approach to the tumor extending to the area IIIB was TfEcDt or TfElDt sacrificing the hearing. TmEnDs was the major approach for tumors localized at area IIA. Higher rate of hearing impairment of the tumors at this area, TmElDs was frequently used. Tumors extending to the area C needed anterior approach in combination with the petrosectomy. Various combination of the TED scale can be designed according to the tumor extension and the patient's neurological status.