Background: Loss of the frontal or forehead bone can occur for a variety of reasons, usually from depressed fractures or loss of a craniotomy flap from infection. With removal of the protective bone cover, the brain and its dural covering sit directly up against the skin not only creating an obvious depression but pulsating with each heartbeat. Forehead reconstruction carries the highest aesthetic demands of any skull defect because it is the most visible in a non-hair bearing area and may involve the brow bone and brow ridge area.
There are almost a dozen methods of forehead skull reconstruction from split-thickness cranial bone grafts to computer-generated custom implant pieces. When skillfully done, any of these reconstructive methods will work satisfactorily. Their various advantages and disadvantages change based on the size of the forehead defect. The larger the bone defect becomes the more a synthetic approach becomes an appealing option.
One well established synthetic cranioplasty material for reconstructive use is hydroxyapatite. Consisting of the inorganic mineral content of natural bone, it is highly biocompatible although it does not get replaced by bone. It ends up creating a dense firm bone-like material that blends smoothly into the surrounding bone edges. It does not have the same strength as the normal double cortical layer skull bone but is strong enough to be an adequate skull substitute.
Besides the aesthetics of forehead skull defects, it is the only skull area which is contiguous with the air-filled frontal sinus cavity. This is a potential source of contamination and is a frequent source of forehead infections if a tissue layer is not created between it and the bone reconstruction material.
Case Study: This 13 year-old teen age boy was involved in a motor vehicle accident and sustained a severely depressed frontal forehead fracture and a large laceration down the center of his forehead. This required an urgent neurosurgical procedure with bone removal and repair of the dura. After three months of healing, he was left with a large depressed central forehead area (10 cm x 6 cm) that extended from the scalp down to the brows with a well healed vertical forehead scar. A 3-D CT scan shows the size of the defect and its involvement with the brow area and the frontal sinus.
Under general anesthesia, the forehead bony defect was accessed through his existing vertical scar from the scalp down to the area between the brows. The skin was lifting off of the dura and the surrounding bone edges. Near the brow area, the frontal sinus cavity was encountered as a 2cm x 2cm hole above the level of the dura.
The frontal sinus was clean and healthy with normal mucosal lining. A large pericranial tissue patch was sutured around all edges to create a thick tissue partition between the frontal sinus and the reconstruction site.
After the pericranial patch was placed, a floor was created for the reconstruction using titanium mesh. Thin 1mm titanium mesh was cut just larger than the bone defect and its edges were slipped under the defect to become a self-locking floor. This not only provided a containment method for the hydroxyapatite cement but keep the dural pulsations off of the hardening reconstruction.
Using a well known hydroxyapatite cement (Mimx, Biomet Microfixation, Jacksonville, FL), the activating liquid and calcium hydroxyapatite powder were mixed together into a putty consistency. This was then poured into the bone defect and molded into shape, recreating the lost brow bone area and the forehead above it. The forehead skin was then closed and scalp scar removed prior to its closure in the hair area.
His surgery was done as an outpatient and he went home the same day. His head dressing was removed the next day and his sutures in the scalp removed ten days later. He had a smooth forehead result right with elimination of the forehead depression and the dural pulsations.
Case Highlights:
1) Reconstruction of the bony forehead can be done by a variety of techniques and hydroxyapatite is a well established cranioplasty material for full-thickness skull defects.
2) Forehead reconstruction which extends down into the brow area must take into account the frontal sinus and have a plan to keep it separate from any implanted material.
3) The properties of hydroxyapatite in a full-thickness skull defect needs reinforcement or a floor to add both strength and a containment method for the material.
Dr. Barry Eppley
Indianapolis, Indiana