Alloplastic Reconstruction of the Calvarium

Peter J. Taub

ANATOMY

The calvarium in the adult is composed largely of an outer cortex or cortical bone, a matrix of cancellous bone and marrow, and an inner cortex of cortical bone.
The specific curvature of the calvarium in the area of the defect should be observed and taken into account when performing the reconstruction.

PATHOGENESIS

Loss of calvarium may have multiple etiologies.
Patients may require craniotomy for tumors, during which the resected bone cannot be replaced at the index procedure secondary to cerebral swelling and the need to avoid increased intracranial pressure.
- The bone graft is left buried in the subcutaneous layer of the abdomen for later replacement.
- Occasionally, the graft becomes infected and can no longer be replaced.
Patients with benign or malignant osseous or soft tissue tumors that invade the bone require resection of a portion of the calvarium (FIG 1).
In cases of trauma, portions of the skull may be shattered such that they cannot be used for reconstruction.
- The mechanism of injury is generally blunt rather than penetrating.
- Prior to the routine installation of seat belts in automobiles, a preponderance of cases was caused by motor vehicle accidents. More recently, assaults have become more prevalent.
- Other causes of skull injury include sports injuries, occupational incidents, and falls.

NATURAL HISTORY

Patients should be medically stable prior to considering cranioplasty.
The timing may also be related to the presence of associated symptoms.
Postcraniectomy patients may present with “the syndrome of the trephined.” This is an infrequent and delayed complication.
- Common radiologic findings include paradoxical herniation, deviation of the midline structures, and sunken skin flap.¹
- The spectrum of symptoms ranges from seizures to headaches to neuropsychiatric disturbance to focal weakness to midbrain syndromes² and parkinsonian symptoms.²^,³

PATIENT HISTORY AND PHYSICAL FINDINGS

In the acute setting, the primary concern for any patient with head injury is possible cervical spine trauma.
Specific signs and symptoms of cervical spine injury include a neurologic deficit, point-specific neck pain, and possible palpable step-off on neck exam.
There may be a noticeable area of deficient bony support for the overlying soft tissues of the scalp (FIG 2).
The laxity of the soft tissues over the defect should be evaluated. Generally, the amount of concavity produced by the defect will match the convexity of the implant. Thus, preoperative tissue expansion is generally not required.
If soft tissues appear to be tight and firm to palpation, tissue expansion should be considered prior to reconstruction.