What is the most likely site of the lesion in a patient with sudden onset of painless diplopia, left eye movement limitation, and ptosis?

The symptoms of sudden onset painless diplopia, left eye movement limitation, and ptosis suggest involvement of cranial nerves responsible for eye movement and lid elevation. In this scenario, the most likely site of the lesion is the cavernous sinus.

The cavernous sinus is a structure located at the base of the skull through which several important cranial nerves pass, including the oculomotor nerve (CN III), trochlear nerve (CN IV), and abducens nerve (CN VI). A lesion in the left cavernous sinus can affect these cranial nerves, leading to symptoms such as diplopia due to impaired eye movement and ptosis from weakness of the levator palpebrae muscle, which is innervated by the oculomotor nerve.

In this situation, the presence of diplopia indicates that there is misalignment of the eyes, commonly due to the dysfunction of one or more of the cranial nerves that control ocular movements. The limitation of left eye movement and ptosis is consistent with the dysfunction of the oculomotor nerve, often impacted by lesions in the cavernous sinus.

Other sites mentioned in the options have different implications: the cerebellopontine angle typically affects hearing and balance along with cranial