What can be seen in a bone window of a cranial Computed Tomography (CT) scan?

What Can Be Seen in a Bone Window of Cranial CT Scan

Bone windows on cranial CT are essential for visualizing osseous structures of the skull, skull base, and temporal bone that cannot be adequately assessed on soft tissue windows or MRI, including fractures, bony erosions, neural foramina abnormalities, and specific pathologic mineralization patterns. 1

Critical Osseous Structures Visualized

Skull Base and Neural Foramina

• Skull base erosions and neural foramina margins are optimally visualized on bone windows using thin-cut high-resolution bone algorithm reconstructions 1
• Temporal bone anatomy including the facial nerve canal, ossicles, and inner ear structures are well characterized on bone windows 2, 1
• Bony contour abnormalities of structures like the sigmoid sinus wall are visible on bone window reconstructions 1

Fracture Detection

• Temporal bone fractures are excellently characterized on high-resolution bone windows, showing the osseous integrity through which cranial nerves course 2
• Skull base fractures including those involving the jugular foramen are detected on bone windows 1
• Subtle nondisplaced fractures of the facial skeleton are identified with thin-section bone window acquisitions 2
• Frontal bone and posterior table fractures are evaluated on bone windows, with displaced posterior table fractures implying dural disruption 2

Pathologic Conditions Visible Only on Bone Windows

Inner Ear and Temporal Bone Pathology

• Superior semicircular canal dehiscence, high-riding jugular bulb, otospongiosis, and Paget disease are conditions invisible on MRI but detectable on bone windows 1
• Sigmoid sinus wall abnormalities causing pulsatile tinnitus are identified on bone window reconstructions from CTA 1

Neoplastic and Inflammatory Disease

• Facial canal foraminal expansion suggesting mass effect or chronic nerve pathology 2, 3
• Patterns of bone erosion indicating tumor involvement or chronic inflammatory disease along neural pathways 2, 3
• Bony remodeling versus lytic destruction distinguishing benign from aggressive malignancies 1
• Inflammatory middle ear disease with facial nerve canal involvement 2, 3

Lesion Mineralization Patterns

• Osseous matrix of osteomas 1
• Chondroid matrix of cartilaginous tumors 1
• Ground-glass density of fibro-osseous lesions like fibrous dysplasia, which appears as characteristic ground-glass ill-defined lesions on bone windows 1, 4
• Intrinsic bone tumor matrices affecting the temporal bone 2, 3

Vascular Pathology Assessment

• Trans-osseous vascular channels and bony erosion patterns suggesting dural arteriovenous fistulas and vascular malformations 1
• Temporal bone anatomy from CTA bone window reconstructions providing osseous details unavailable on MRA/MRI 1

Technical Requirements for Optimal Visualization

• Thin-cut high-resolution bone algorithm windows (1 mm or less) through the skull base are necessary for characterizing subtle osseous changes 2, 1, 3
• Multiplanar and 3-D image reconstructions allow better characterization of complex fractures, with 3-D reformations being critical for preoperative surgical planning 2

Critical Clinical Pitfalls to Avoid

• Never rely solely on soft tissue windows when evaluating cranial CT, as critical bony pathology including fractures, erosions, and foraminal abnormalities will be missed 1
• Do not assume MRI can substitute for bone window CT in temporal bone or skull base evaluation, as MRI cannot adequately visualize cortical bone detail, dehiscences, or subtle erosions 1
• Failing to use thin-cut high-resolution bone algorithm reconstructions through the skull base results in missed subtle fractures and foraminal abnormalities 1
• Normal bony discontinuities representing sutures, fissures, and neurovascular foramina should be differentiated from true fractures 5