Secondary treatment of acquired cranio-orbital deformities

Introduction

Acquired cranio-orbital deformities comprise a vast array of etiological entities which result in defects, disproportions, or asymmetries in the upper face and skull, and they are commonly associated with functional visual and neurological disturbances. Reconstruction poses a unique set of challenges. Restoration of the complex surface topography and structural integrity of the skull and orbits, while maintaining visual, oculomotor, and neurological functions, is the primary objective.

Although the principles of cranio-orbital reconstruction were established in the mid 20th century, recent advances in medical imaging, computer modeling, and rapid prototyping technologies have revolutionized how we assess and confront these surgical challenges. The advent of 3D imaging and quantitative analysis of morphology, intra-operative navigation techniques, 3D modeling, and rapid prototyping of patient-specific implants, templates, and surgical guides has greatly enhanced preoperative surgical planning and optimized outcomes.

This chapter briefly summarizes the surgically relevant anatomy of the cranium and orbit, describes preoperative clinical and radiological assessment, discusses direct applications of computer imaging, modeling, and rapid prototyping, and presents treatment algorithms for both cranial and orbital reconstruction.

Relevant anatomy

Orbit

The orbital cavities are paired, symmetrical cavities located between the skull and midface. Each orbit features a pyramidal shape, starting as a four-sided pyramid along the orbital rims and tapering into a three-sided pyramid towards the apex ( Fig. 5.1 ) where the floor and medial wall merge. The longitudinal axis of each pyramid is oblique, oriented in an inferolateral to superomedial direction from base to apex.

The bony orbit is subdivided into two main components for surgical considerations ( Fig. 5.2 ):

• 1.

  The deep orbital cavity or orbital apex is the fixed segment of the orbital cavity, which accommodates the critical structures passing through the optic foramen and superior orbital fissure.

• 2.

  The circumferential bony rim of the orbit is composed of thick resilient bone which defines the shape and dimensions of the orbital aperture. This is the movable orbit, which can be safely transposed in any direction, in one or multiple segments. Precise anatomical restoration is a prerequisite for accurate restoration of globe position, as well as palpebral fissure width and inclination.

Historical perspective

Current principles of cranio-orbital reconstruction are based primarily on the teachings of Dr. Paul Louis Tessier (1917–2008). In the mid 1950s, while at Hôpital Foch in Paris with Gerard Guiot and in London alongside Sir Harold Gillies, Dr. Tessier pioneered craniofacial surgery. The novel surgical approaches and techniques which he developed allowed reconstruction of complex congenital craniofacial malformations with unprecedented safety and efficacy. These principles were readily adopted in the reconstruction of acquired cranio-orbital deformity. The following fundamental guidelines established by Dr. Tessier are still highly relevant today:

• ■

  Segments of the bony facial skeleton can be entirely stripped of periosteum, osteotomized, and transposed to a new anatomical location, with the expectation of consolidation and shape preservation. Furthermore, autogenous bone grafts placed within residual bony gaps lead to more stable long-term outcomes.

• ■

  The orbital soft-tissue contents can be freely mobilized within a periorbital cone pedicled on the orbital apex and superior orbital fissure, without adversely affecting ocular, oculomotor, palpebral, or lacrimal function. As such, the orbits and eyes can be safely translocated vertically or horizontally, as needed, over a considerable distance.

• ■

  Combined intracranial and extracranial exposure allows safe retraction of both cranial and orbital contents for direct visualization of deeper or more critical structures in the fronto-orbital or nasoethmoid regions.

Adherence to these principles ensures optimal protection of critical structures while manipulating facial skeletal segments to meet the specific reconstructive requirements in any patient.

Classification of acquired cranial deformity

Acquired cranial deformities are best classified etiologically ( Box 5.1 ). The vast majority of deformities feature “known” or established full-thickness skull defects, such as those resulting from prior trauma, craniectomy, or craniotomy with failed bone flap replacement ( Fig. 5.4 ). Less common are “unknown” or intra-operative defects of the cranium, such as those resulting from surgical excision or ablation of pathological lesions. For these “unknown” defects, the size and shape of the skull defect cannot yet be predicted, as the precise dimensions are determined intra-operatively during lesion resection.

Cranial infections include those resulting from infected mucocele ( Fig. 5.5 ) or sinusitis, infected hardware or cranioplasty implant, and from osteomyelitis. In these clinical settings, source identification and proper antibiotic treatment are sought out prior to any reconstructive planning.

Generalized calvarial hypertrophy, sclerosis, atrophy, or rarefaction require specific investigations to rule out any underlying metabolic or endocrinologic disorders. While complete cure of the bony disease is unlikely, reconstruction of deformities resulting from debulking procedures is aimed at improving normal surface contour.

Bone tumors of the cranial vault, both benign and malignant, can present as primary lesions ( Figs. 5.6 & 5.7 ) or appear following contiguous or metastatic spread ( Fig. 5.8 ). These neoplastic lesions can arise from varying tissue cell origins, such as bone, cartilage, skin, connective tissue, salivary glands, vasculature, or any combination of these. Furthermore, skin tumors of the scalp, such as basal cell and squamous cell carcinomas, can exhibit aggressive and rapid growth, infiltrating underlying bone. Before commencement of bony reconstruction, resection of involved soft and bony tissue needs to extend to healthy surgical margins.

Classification of acquired orbital deformity

Acquired orbital deformities are classified according to the oculo/orbital malposition or defect ( Box 5.2 ). This classification serves to direct treatment options, while guiding relevant surgical investigations and planning.