The Clival Chordoma Understanding 6th Nerve Palsy
The Clival Chordoma Understanding 6th Nerve Palsy The clival chordoma is a rare, slow-growing malignant tumor that originates from remnants of the notochord, a primitive structure in embryonic development. Located at the base of the skull, specifically in the clivus—a bony section situated behind the nasal cavity and beneath the brain—these tumors pose significant diagnostic and therapeutic challenges due to their proximity to critical neurovascular structures. One of the notable clinical manifestations associated with clival chordomas is sixth nerve palsy, which can serve as a key indicator of tumor progression or involvement.
Understanding the anatomy of the sixth cranial nerve, also known as the abducens nerve, is essential to appreciate how a clival chordoma can impact it. The sixth nerve supplies the lateral rectus muscle, responsible for outward movement of the eye. When this nerve is compromised, patients often present with horizontal diplopia (double vision) and an inability to move the affected eye outward. The nerve’s lengthy intracranial course makes it particularly vulnerable to lesions in the skull base, especially those involving the clivus.
The pathophysiology of sixth nerve palsy in the context of a clival chordoma involves direct tumor invasion, compression, or displacement of the nerve along its course. As the tumor enlarges, it may erode the clival bone and extend into the adjacent foramina, such as Dorello’s canal, through which the nerve passes. Consequently, patients may initially experience subtle symptoms, but as the tumor progresses, the palsy becomes more pronounced, often accompanied by other cranial nerve deficits if the tumor involves neighboring structures.
Diagnosing a clival chordoma requires a combination of clinical evaluation and imaging studies. Neurological examination revealing sixth nerve palsy prompts further investigations, primarily magnetic resonance imaging (MRI). MRI provides detailed visualization of the tumor’s size, extent, and its relationship with surrounding structures. Characteristically, clival chordomas appear as
midline masses with heterogeneous signals, often showing lobulated contours. They may also demonstrate bony erosion on computed tomography (CT) scans, emphasizing their invasive nature.
Management of clival chordomas is complex and multidisciplinary, involving neurosurgeons, otolaryngologists, radiation oncologists, and radiologists. Surgical resection is typically the first step, aiming to remove as much tumor tissue as possible while preserving neurological function. Given the tumor’s location, approaches such as the transnasal endoscopic route have gained prominence for their minimally invasive nature and improved visualization. However, complete resection is often challenging due to the tumor’s infiltrative characteristics and proximity to vital structures.
Postoperative radiotherapy, including proton beam therapy, is frequently employed to target residual tumor tissue and reduce recurrence risk. Due to the tumor’s propensity for local recurrence, long-term follow-up with imaging is essential. Symptom management, including addressing cranial nerve deficits like sixth nerve palsy, may involve prisms for diplopia or, in some cases, surgical intervention.
In conclusion, the relationship between clival chordomas and sixth nerve palsy underscores the importance of early recognition and comprehensive management of skull base tumors. Awareness of the clinical signs can facilitate prompt diagnosis, potentially improving outcomes and preserving neurological function.
