What is the petrous bone?

What is the Petrous Bone?

The petrous bone (also called the petrous portion or petrous pyramid) is a dense, pyramid-shaped part of the temporal bone that forms a critical component of the skull base, housing the inner ear structures, internal auditory canal, and serving as a conduit for major neurovascular structures. 1, 2, 3

Anatomical Structure and Location

• The petrous bone is one component of the temporal bone, which consists of four parts: the squamous portion (pars squamosa), tympanic portion (pars tympanica), mastoid portion (pars mastoidea), and the petrous portion itself 4, 2

• It is a pyramid-shaped bony structure located at the base of the skull, positioned between the sphenoid and occipital bones 2, 3

• The petrous bone is the densest bone in the human body, providing protection for the delicate structures it contains 5, 3

Key Anatomical Contents

The petrous bone can be understood through a compartmental approach with four main components 3:

Vascular Structures

• The internal carotid artery traverses through the carotid canal within the petrous bone before entering the intracranial space 1
• The jugular bulb is located within the jugular foramen at the posterior aspect of the petrous bone 1
• High-riding jugular bulb represents a common anatomical variant identifiable on imaging 1

Neural Structures

• The internal auditory canal runs through the petrous bone, carrying the facial nerve (cranial nerve VII) and vestibulocochlear nerve (cranial nerve VIII) 1, 2, 3
• The facial nerve has a complex course through the petrous bone, making it vulnerable to injury in trauma or surgical procedures 3

Inner Ear Components

• The petrous bone houses all inner ear structures, including the cochlea, vestibule, and semicircular canals 4, 2, 3
• The superior semicircular canal can develop pathologic dehiscence (SSCD), which is detectable on high-resolution CT 1

Clinical Significance

Trauma

• Petrous bone fractures are among the most common skull base fractures, typically resulting from high-energy trauma 5
• These fractures carry significant risk due to the critical neurovascular structures contained within the petrous bone 5
• Fractures can result in facial nerve injury, hearing loss, vestibular dysfunction, and vascular complications 5

Pathology

• The petrous bone can be affected by inflammatory diseases, infections, cholesteatomas, and tumors 4, 6
• Petrous bone cholesteatoma is a rare but important pathology that grows slowly and often presents with hearing loss (94% of cases) and facial paralysis (55% of cases) 6
• Skull base tumors such as leiomyomas and angioleiomyomas can involve the petrous bone, though this location is uncommon 7

Imaging Considerations

• High-resolution CT without contrast is the optimal modality for evaluating petrous bone anatomy, demonstrating bony canal anatomy, dehiscences, vascular variants, and semicircular canal integrity 1
• The intrinsic sloping of the petrous temporal bone requires oblique reformats (Stenver and Pöschl planes) to accurately assess structures and avoid overestimating pathology such as superior semicircular canal dehiscence 1
• MRI with gadolinium contrast is useful for evaluating soft tissue pathology, neural structures, and vascular lesions involving the petrous bone 7

Surgical Relevance

• Surgical approaches to the petrous bone require specialized skull base expertise due to the complexity of the region and proximity of critical neurovascular structures 8
• Multiple surgical corridors exist for accessing petrous bone pathology, with approach selection dependent on the specific location and type of lesion 3, 6
• The compartmental organization of the petrous bone (mucosal, cutaneous, neural, and vascular compartments) provides a framework for understanding surgical anatomy and planning approaches 3