**Core Concept**
The spread of infection from the central nervous system (CNS) to the inner ear is a critical concept in otolaryngology, particularly in the diagnosis and management of labyrinthitis and other inner ear infections. This phenomenon is often due to the spread of infection through various anatomical pathways that connect the CNS to the inner ear.

**Why the Correct Answer is Right**
The cochlear aqueduct is a bony canal that connects the perilymphatic space of the cochlea to the subarachnoid space of the CNS. It allows for the exchange of cerebrospinal fluid (CSF) and perilymph, and is a potential pathway for the spread of infection from the CNS to the inner ear. Infection can enter the inner ear through this aqueduct, leading to labyrinthitis, which is characterized by inflammation of the inner ear structures.

**Why Each Wrong Option is Incorrect**
**Option B:** The endolymphatic sac is a structure located in the posterior fossa, outside the inner ear, and is involved in the regulation of endolymph pressure. While it may be affected by inner ear infections, it is not a primary pathway for the spread of infection from the CNS to the inner ear.

**Option C:** The vestibular aqueduct is a bony canal that contains the endolymphatic duct and sac, and is involved in the drainage of endolymph from the inner ear. While it may be affected by inner ear infections, it is not a primary pathway for the spread of infection from the CNS to the inner ear.

**Option D:** The hylle fissure is not a well-defined anatomical structure in the inner ear, and is not a recognized pathway for the spread of infection from the CNS to the inner ear.

**Clinical Pearl / High-Yield Fact**
The spread of infection from the CNS to the inner ear is often associated with symptoms such as vertigo, hearing loss, and tinnitus, and requires prompt diagnosis and treatment to prevent permanent damage to the inner ear structures.

**✓ Correct Answer: A. Cochlear aqueduct. The cochlear aqueduct is a bony canal that connects the perilymphatic space of the cochlea to the subarachnoid space of the CNS, allowing for the potential spread of infection from the CNS to the inner ear.**