Helpful and unhelpful parts of the superior petrosal triangle.

BACKGROUND: The root of zygoma-head of malleus line may guide to the internal auditory canal, but few anatomic studies address its accuracy.

HYPOTHESES: The precision of measurements is excellent, the "superior petrosal triangle" components (foramen spinosum, root of zygoma, and head of malleus) have a consistent relationship and accurately guide to Bill's bar, and distances correlate with pneumatization.

METHODS: Forty-one bequeathed adult human cranial base specimens (82 temporal bones) were dissected in a surgical manner.

RESULTS: Measurements had excellent repeatability. The root of zygoma-head of malleus reference line always projected onto or posterior to Bill's bar, but distances measured had wide ranges. No measurement correlated with pneumatization.

CONCLUSION: The root of zygoma-head of malleus line extends onto or posterior to Bill's bar. Measurement guides to the head of the malleus are not predictable.