The internal occipital protuberance is the central projection on the inner surface of the occipital bone where the falx cerebri, tentorium cerebelli, and superior sagittal sinus converge at the torcular Herophili (confluence of sinuses). The cruciform eminence radiates from this point in four directions: superiorly to the sagittal groove, laterally along the transverse grooves, and inferiorly along the occipital crest.
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| Ossification | Lies on the squamous occipital, near the junction of its membrane-formed upper part and cartilage-formed lower part. |
The internal occipital protuberance marks the torcular Herophili, the confluence of the superior sagittal, straight, and transverse sinuses. Posterior fossa craniotomy and occipital craniectomy must account for this structure to avoid catastrophic sinus injury. On MRI and CT, the torcular Herophili is often asymmetric. The left transverse sinus is dominant in 75% of individuals. Occipital meningiomas arising near the torcular require particular attention to sinus anatomy for safe resection.
Occipital bone flap elevation crossing the internal occipital protuberance risks the torcular Herophili where the superior sagittal, straight, and transverse sinuses converge; preoperative MRV or CTV maps sinus anatomy, and the bone flap is planned to stay lateral to the torcular to avoid catastrophic sinus laceration.
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