Guidelines for Removal of Temporal Bones for Pathological Study
- The temporal bones should be removed as soon as possible.
- If the body is not refrigerated, removal should take place within eight hours.
- If the body is refrigerated and/or embalmed, they should be removed within 48 hours (12-24 hours if possible).
- Before the brain is removed, the seventh and eighth cranial nerve trunks should be purposely cut at the entrance of the internal auditory canal (porus acousticus) to avoid traumatic avulsion from the internal auditory canal.
- The temporal bones should be placed immediately into jars of 10% neutral buffered formalin. If the brain has been removed, it should also be fully submerged in a container with plenty of 10% neutral buffered formalin.
- The specimens should then be refrigerated (if available) in the formalin solution for 7 days. If no refrigeration is available, room temperature will be fine.
- Allow the specimens to soak for about one week before shipping.
- Specimens should be shipped in formalin soaked gauze, bagged and then placed into watertight containers with the tops securely taped. Shipping materials (box, jars, watertight bags, and labels) will be forwarded to you.
- If the specimens are severely damaged during removal, the Registry and its collaborating laboratories exercise the option to not accept them.
Temporal bone specimens should fit the following criteria:
- The entire middle ear and inner ears must be intact.
- Most of the mastoid should be present.
- Some external auditory canal should be present.
- The trunks of the seventh and eighth cranial nerves should be visible at the entrance of the internal auditory canal (indicating that the nerve trunks are intact within the temporal bone)
If you have any questions, please contact the Registry, 24 hours a day at (800) 822-1327.
A. Necessary instruments
- Stryker autopsy motor
- Oscillating saw
- Ferguson bone-holding forceps
- Osteotome and Mallet
- Heavy scissors
- Kelly clamp
- Heavy silk suture
B. Removal of the Brain
The brain is elevated from the floor of the skull sufficiently to expose the trunks of cranial nerves VII and VIII. These must be cut at the meatus of the internal auditory canal.
Note: Failure to do this will frequently result in avulsion of these nerves from the canal, which detracts from the value of the specimens.
Removal of Brainstem
If the auditory brain has been donated, the auditory brain stem should also be removed.
Note: If unsure of how to separate the brain stem from the cerebellum, it is better to send the entire brain intact to avoid destroying the cochlear nucleus when removing the cerebellum.
Storage of Brain and Brainstem
Brain tissue should be placed in cold 10% neutral buffered formalin (fully submerge and cover the specimen).
Brain and brainstem removal video
Methods of Temporal Bone Removal
The right and left temporal bones can be removed by either the block or bone plug method. The block method can be done with mallet and osteatome or with the motor-driven oscillating, rocker-type saws, both of which are standard equipment in autopsy rooms.
C. Bone plug method
This method consists of using the bone plug cutter in the oscillating motor driven saw. For the adult body, the proper saw diameter is 1- 1/2 inches.
Plug removal method video
- The saw is centered on the arcuate eminence and is advanced through the skull base perpendicular to the floor of the middle cranial fossa.
- The head should be steadied by an assistant.
- The cutter can be irrigated with water to improve its cutting action.
- A loss of resistance is felt when the cutter has traversed the skull base.
- The bone plug is grasped with bone forceps and gradually extracted by forceful pulling and rotating of the bone plug.
- The carotid artery is identified and grasped with a hemostat, following which the inferior attachments of the specimen are severed with knife, scissors or osteatome. The internal carotid artery is ligated and the external auditory canal is closed by suture or suitable clamp.
D. Block method
Four cuts are made in the bone of the skull base on both the right and left side.
Part 1 - Making the Cuts
Part 2 - Removing blocks
- Cut 1 is made in the lateral part of the floor of the middle cranial fossa and passes through the cartilaginous part of the external auditory canal and lateral aspect of the mastoid bone.
- Cut 2 is made at the petrous apex perpendicular to the pyramid.
- Cut 3 is made parallel to and 2 inches anterior to the petrous ridge.
- Cut 4 is an undercut of the block of tissue outlined by the preceding 3 cuts. It is made in the floor of the posterior cranial fossa parallel and adjacent to the petrous pyramid.
Block removal method video
- The block is engaged with a bone grasping forceps and forcibly retracted.
- The internal carotid artery is identified and grasped with a hemostat, after which an osteatome scissors or knife is used to sever the remaining fibrous and ligamentous attachments.
- Care should be used to avoid crushing the specimen with the bone grasping forceps.
- The internal carotid artery is ligated and the external auditory canal is closed by suture or suitable clamp.