Introduction: Traditional Kawase’s approach(Arcuate eminence(AE),GSPN,Petrous ridge(PR)) provides 10x5mm fenestration at petrous apex between Vnv. and internal auditory canal. Despite permitting key access,exposure is conical and crowded; it does not allow proper exposure to the Vnv exiting from tentorium, VIth nerve in Dorello canal and posterior clinoid process. Modified technique of additional trans-cavernous exploration and medial mobilization of Vnv. results in posterior cavernous anterior transpetrosal posteromedial Modified Dolenc-Kawase(MDK)-rhomboid approach.

Methods: Dissection of posterior cavernous sinus wall over the V1,V2,V3 and Gasserian Ganglion(GG) permits access to MDK-rhomboid(AE-posterior,GSPN-lateral,PR-medial and V3+GG-anterior). Ligation and division of superior petrosal sinus at posterior clinoid process and elevation+mobilization of Vnv. permits enlarged view of previous inaccessible areas. Spectrum of patients with posterior cavernous+petroclival lesions were treated with this approach. Volumetric analysis of temporal bones with 3D laser scanning of dry and drilled bones for respective triangles and rhomboid areas; comparing difference of exposure with traditional versus modified approaches on cadaver dissection were analyzed for evaluation of area exposed, surgical freedom and angulation of approach.

Results: MDK rhomboid provides 1.5X larger area and 2.0X greater volume of bone at anterior petrous apex in comparison to Kawase’s triangle. Cadaver dissection objectified technical feasibility of MDK approach providing nearly 1.5 to 2 times larger fenestration with improved view and angulation to posterior cranial fossa. MDK rhomboid approach was used in the treatment of petroclival meningiomas(35),giant dumbell trigeminal schwannoma(11),clival chordoma(6),clival chondrosarcoma(4),trochlear schwanomma(1),giant posterior fossa craniophrangioma(6), middle+posterior fossa epidermoid(4),hypothalamic hamartoma(1),giant low basilar bifurcation aneurysm(2),petroclival hemangiopericytoma(1) and histiocytosis(Rosai Dorfman).

Conclusions: MDK rhomboid approach is technically demanding and requires thorough knowledge of anatomy and pathology; it provides safe corridor during the microsurgical treatment of spectrum of skull base lesions. The larger fenestration at petrous apex provides greater surgical freedom at Dorello’s canal, Gasserian ganglion and prepontine area and better anteroposterior angulation in comparison to traditional Kawase’s approach.

Patient Care: Posterior cavernous anterior transpetrosal posteromedial Modified Dolenc-Kawase(MDK)-rhomboid approach is a safe approach for treatment of wide spectrum of central and posterior fossa lesions.

Learning Objectives: 1. Posterior cavernous anterior transpetrosal posteromedial Modified Dolenc-Kawase(MDK)-rhomboid approach is technically demanding and requires thorough knowledge of anatomy and pathology. 2. MDK Rhomboid approach provides safe corridor during the microsurgical treatment of spectrum of skull base lesions. 3. The larger fenestration at petrous apex provides greater surgical freedom at Dorello’s canal, Gasserian ganglion and prepontine area and better anteroposterior angulation in comparison to traditional Kawase’s approach.

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