Surgical Anatomy of a Markedly Developed Rhomboid Lip During Cerebellopontine Angle Meningioma Resection: Radiological and Histopathological Correlation.

OBJECTIVE: The rhomboid lip (RL) is a variable sheet-like neural structure extending from the lateral recess of the fourth ventricle into the cerebellopontine angle (CPA). This technical note describes the radiological, microsurgical, and histopathological features of a markedly developed RL encountered during CPA meningioma surgery, with emphasis on its intraoperative identification and selective surgical management.

METHODS: A 60-year-old woman underwent retrosigmoid resection of a 12-mm left CPA meningioma. Preoperative magnetic resonance imaging suggested a well-developed RL extending from the foramen of Luschka toward the internal auditory canal. Intraoperatively, the RL was assessed according to its morphological features and anatomical relationships and was preserved or selectively divided according to the exposure required during tumor removal. RL tissue that required division for surgical exposure was subsequently examined histopathologically.

RESULTS: The RL appeared thicker and less transparent than the arachnoid, with veins coursing along its surface. Its relationship with cranial nerve IX and the choroid plexus provided useful anatomical landmarks for identification. The portion overlying the vestibulocochlear nerve was preserved during most of the tumor dissection and divided only when additional exposure was required for complete tumor removal. Histopathological examination demonstrated ependymal and glial layers, confirming the structure as RL. Simpson grade II resection was achieved without new cranial nerve deficits.

CONCLUSIONS: A well-developed RL can be recognized as a distinct anatomical structure using morphological and anatomical landmarks. During CPA surgery, selective preservation or division according to the evolving operative corridor may facilitate anatomically informed surgical dissection.