ARTÍCULO ESPECIAL

 

Anterior subcranial approach. Discussion and historical review of the surgical technique

Abordaje subcraneal discusión y revisión histórica de la técnica quirúrgica

 

 

 

I. Zubillaga Rodríguez¹, G. Sánchez Aniceto¹, J.J. Montalvo Moreno², R. Díaz Lobato³

1 Médico Adjunto. Servicio de Cirugía Oral y Maxilofacial.
2 Jefe de Servicio. Servicio de Cirugía Oral y Maxilofacial.
3 Jefe de Servicio. Servicio de Neurocirugía.
Hospital Universitario 12 de Octubre. Madrid. España.

Correspondence

 

 

 

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ABSTRACT

Introduction. Skull base surgery is now a reality that has become consolidated over the last decades. The dizzyingly rapid technological advances that have taken place have served as a motor for the development of surgical techniques to approach this anatomic region. The foundation for the definitive push forward of this technique was multidisciplinary teamwork.
Material and methods. The subcranial approach is described as an alternative to traditional approaches to the skull base. The history of different key steps in the subcranial approach is described and discussed.
Discussion. The selection of the most suitable approach to the skull base in each case is essential for obtaining satisfactory surgical results overall. Initially, the selection of an approach depends on the exact anatomic location of the lesion in the skull base, its threedimensional extension, as well as the nature of the lesion. The subcranial approach is an important step in the development of surgical techniques for the skull base.
Conclusions. The anterior subcranial approach provides ample and optimal exposure of all the planes of the anterior cranial fossa, from the anterior ethmoidal roof to the clivus-sphenoid plate, including the orbital roofs. This objective is achieved without having to retract the frontal lobes, thus avoiding the associated morbidity and mortality that this maneuver entails. The anterior subcranial approach makes precise earlier management of oncologic pathology with intradural and extradural involvement possible, as well as the treatment of fractures produced by high-energy impact with involvement of the anterior cranial fossa.

Key words: Subcranial approach; Anterior cranial fossa.

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RESUMEN

Introducción. La cirugía de la base craneal es en la actualidad una realidad que se ha ido consolidando en las últimas décadas. El vertiginoso avance tecnológico desarrollado ha actuado como motor en la evolución de las técnicas quirúrgicas que abordan dicha región anatómica. Su impulso definitivo se ha cimentado en el concepto básico de equipo multidisciplinario.
Material y métodos. Se describe el abordaje subcraneal como alternativa a los tradicionales abordajes a la base craneal anterior. Discusión y revisión histórica de los distintos pasos claves en la realización del mismo.
Discusión. La elección del abordaje más adecuado a la base craneal en cada caso es esencial para la obtención de resultados quirúrgicos globales satisfactorios. Inicialmente dependerá de la localización anatómica exacta de la lesión dentro de la base craneal y de su extensión tridimensional, así como de la naturaleza de la misma. El abordaje subcraneal representa un paso importante en el desarrollo de las técnicas quirúrgicas de la base craneal.
Conclusiones. El abordaje subcraneal permite una amplia y óptima exposición de todos los planos de la fosa craneal anterior, desde el techo etmoidal anterior hasta el clivus-planum esfenoidale incluyendo los techos orbitarios. Este objetivo se logra sin retracción de los lóbulos frontales evitando de esta manera la morbimortalidad asociada que dicha maniobra conlleva. Favorece el manejo precoz preciso de patología oncológica con afectación intra-extradural y el tratamiento de fracturas tras impactos de alta energía con afectación de la fosa craneal anterior.

Palabras clave: Abordaje subcraneal, fosa craneal anterior.

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Introduction

Skull base surgery is now a reality as a result of its consolidation over the last decades. The dizzyingly rapid technological advances that have taken place, including more specific preoperative imaging techniques, have served as a motor for the development of surgical techniques to approach this anatomic region. Increased knowledge of the anatomy of the skull base also has stimulated the development of new surgical approaches. The foundation of its definitive push forward was the fundamental concept of multidisciplinary teamwork¹. The presence of qualified teams consisting of neuroradiologists, including interventional specialist, anesthetists, neurosurgeons, and maxillofacial surgeons has been established as technically and ethically necessary for treating pathology of this complex anatomic area with strict competence and guarantees.

The selection of the most suitable approach to the skull base for each patient is essential for obtaining satisfactory surgical results overall. Initially, the selection depends on the exact anatomic location of the lesion in the skull base and its three-dimensional extension, as well as the nature of the lesion. Possible options must be discussed in the light of the patient’s overall status, the planned reconstruction, and the experience of the surgical team.

The anterior subcranial approach was described in 1978 by Raveh² for the treatment of trauma that affected the anterior skull base and as an alternative to the traditional transcranial-transfacial approaches used to obtain access to this region. The approach is based on the pioneering studies of Frazier, Smith, and Ketcham, who demonstrated the possibilities of transfacial approaches and after the advances made by Tessier and Derome in developing the transbasal approach. Later studies by Lawton, Fukuta, Janecka, and Sekhar³ contributed to the definitive development of this approach. It later was used in the correction of congenital craniofacial malformations. In 1980 its use in oncologic surgery of the skull base was described for the first time.

The anterior subcranial approach is an important step in the design of surgical techniques for the skull base. It is a logical step forward in making osteotomies available that has resulted from the effort of and cooperation between the different specialties that work with conditions of the skull base. The anterior subcranial approach offers ample and optimal exposure of all the planes of the anterior cranial fossa, from the anterior ethmoidal roof to the clivus-sphenoid plate, including the orbital roofs. This objective is achieved without having to retract the frontal lobes, thus avoiding the associated morbidity and mortality that this maneuver entails. The subcranial approach makes possible the precise and early management of oncologic pathology with intradural and extradural involvement, the treatment of fractures after high-energy impact with involvement of the anterior cranial fossa, including dural tearing and brain tissue herniation, decompression of the optic nerve, the correction of craniofacial malformations, and rigorous isolation and reconstruction of the skull base.

An important aspect in the "survival" of a new field of medicine is its acceptance as a practical alternative to historical standards. This goal is achieved through education and by obtaining factual knowledge of the benefits, risks, and limitations that introducing it into daily practice involves.

The development of instrumentation material has been relevant to the development of surgery of the skull base. It has been a key to all the phases of our clinical practice: from diagnosis to postoperative follow-up, passing through intraoperative monitoring.

Reconstructive aspects of skull base surgery have been gaining interest. Reconstruction is an indispensable phase of any complex surgical procedure. The more that critical anatomic structures are affected by surgery, the greater is the demand for integral reconstruction. Nowadays, not only is adequate resolution of skull base pathology conceivable, but achieving notable aesthetic and functional results are mandatory. Current knowledge and techniques make possible and advisable early, aggressive and definitive treatment of skull base pathology in a single surgical intervention. Any defect in the skull base that produces direct communication of the intracranial content with the nose and/or paranasal sinuses requires reconstruction.⁴

The perfection of different reconstructive techniques, including microvascularized free flaps and osteosynthesis materials,⁵ has lent new impulse to a dramatic reduction in morbidity and mortality rates. The needs of both improving accessibility and reconstructing the skull base have progressively drawn maxillofacial surgeons into the multidisciplinary management of this conditions in this location.

 

Material and method. Discussion

The key steps in executing the anterior subcranial approach are discussed below and the history of different therapies applied in this anatomic region is reviewed.

The coronal approach offers more visibility and control of the region to be treated while allowing the harvest of autologous bone grafts in the same surgical field. This is the approach of choice in the immense majority of cases for the management of anterior skull base pathology. The pericranium must be preserved because it may be useful for sealing the anterior skull base.

The classic bicoronal incision is modified. At present, a zigzag incision is made that begins at the root of the helix and continues posteriorly. This ensures the preservation of the superficial, temporal vessels, which are useful not only as a nutrient pedicle for the local flaps used in cranial reconstruction, but also as receptor vessels if microsurgical reconstructive techniques are required.

A large variety of techniques have been used to access the frontal sinus, such as preparing bone flaps or sinus transillumination to develop free bone grafts of the anterior table of the frontal sinus.

Surgery of the frontal sinus has progressed in parallel with the development of treatment for craniofacial trauma.

The first attempts to access the frontal sinus included simple percutaneous drainage by trepanation in cases of acute sinusitis. Satisfactory results rarely were obtained.

The first operation for fracture of the frontal sinus was described by Reidel in 1898. This author performed total sinus exenteration, thus creating collapse of the frontal flap onto the posterior wall. In order to minimize the aesthetic defect of the Reidel procedure, Killian in 1904 performed a similar operation but preserved 10 mm of the supraorbital rim for cosmetic purposes. In 1921, Lynch performed frontoethmoidectomy, resecting the floor of the frontal sinus, ethmoid, and nasal middle turbinate bones. The incidence of complications with this procedure was comparable to that of the most radical procedures of Reidel and Killian.

The next significant advance in the management of fractures of the frontal sinus was achieved in 1951, when Bergara and Bergara developed the "osteoplastic flap."

The technique for preparing a bone flap in surgery of the frontal sinus was first described by Kocher in the 19^th century. Attempted osteotomy of the anterior table as a single unit was performed by Tato and later by Goodale and Montgomery² for the management of frontal chronic sinusitis.

Molds were made using the form of the frontal sinus based on plain skull radiography (the magnification factor has to be considered). This mold was sterilized at the time of surgery and used to delineate the perimeter of the frontal sinus. An osteotomy was made according to this perimeter and the anterior table was pediculated from the frontal pericranium. Another technique uses transillumination to delimit the edges of the frontal sinus.

Current concepts and principles are based on earlier surgery undertaken to obtain stable aesthetic and functional results. At present, CAT type craniofacial imaging techniques allow the evaluation of sinus form and size, thus facilitating the later quadrangular access osteotomy to the anterior wall of the frontal sinus.

The approach to the frontal, ethmoidal, and sphenoid sinuses is practically impossible without a procedure involving the section of part of the cranial bone, Hayes Martin,1948.

Sometimes the osteotomy of approach to the frontal sinus is modified following the fracture pattern of the anterior wall of the frontal sinus (Fig. 1). Removal of the fractured bone fragments from the anterior wall gives access to the sinus. These fragments are conserved in saline solution and repositioned anatomically after proper treatment of the frontal sinus. Proper planning of the bone flap is essential and should take into consideration the existing fractures. The final goal is to precisely expose and manage the traumatic frontal pathology. The bone flap may include the nasal bones. In these cases, the canthal ligaments are attached by nonresorbible suture to the anterior wall of the contralateral frontal sinus by passing it behind the nasofrontal segment (transnasal canthopexy). This correctly positions the medial canthii in the vertical, horizontal, and sagittal planes. Some authors 6 preserve the distal 3-5 mm of the intact nasal bones to maintain the functionality of the internal nasal valves. The size of the bone flap and amount of orbital rim included in the flap are determined by the amount of frontal cavity that has to be exposed when designing the osteotomy of the anterior wall of the frontal sinus (Fig. 2).

As the size of the bone flap is known before the osteotomy is completed, it is possible at that time to preinsert the miniplates that will attach the osteotomy to its definitive position (Fig. 3). These miniplates are partially removed (the screws that attach it to the bone flap are loosened and the flap is rotated) and the anterior wall osteotomy is completed and the sinus is opened (Fig. 4). The osteotomy is made with a sagittal saw. The sagittal saw allows a beveled-edge upper osteotomy to be made during flap harvest, which is a safety measure to avoid penetrating the central nervous system through the anterior cranial fossa. Insertion of an osteotome behind the glabella allows the flap to be separated from the crista galli, thus impeding the penetration of the frontal dura mater. Precise final positioning of the bone flap ensures adequate frontal reconstruction.

Primary ossification occurs if the osteotomy is narrow enough and the bone flap is repositioned and attached firmly by osteosynthesis.

If the underlying pathology affects only one frontal sinus and the intersinusal septum is not affected, there is no indication for eliminating this septum. It is clear that only the affected frontal sinus will require surgical treatment, which will be given only if the septum is intact.

Independently of the pathologic process involved, the surgical approach to the frontal sinus must allow adequate exposure and management of the sinus. Once the sinus cavity has been opened and the pathologic process is treated, the mucosa of the frontal sinus is carefully removed from the sinus walls, which then are abraded (Fig. 5). This eliminates the invaginations of the sinus mucosa, thus reducing postoperative complications. Abrasion of the bone walls also increases the useful vascular supply to the filler used to pack the frontal sinus.

The anatomic bases for eliminating the internal cortex of the bone by abrasion were described in 1933 by Mosher and Judd. They described small depressions in the internal cortical layer that allow the diploic veins of Breschet to pass through. These veins connect the mucosa with the dural veins. The author insists on the need to eliminate these depressions as potential sites of mucous retention.

Holding, in studies of the frontal sinus in dogs, showed that incomplete elimination of the mucous membrane leads to incomplete sinus obliteration with maintenance of an air cavity and later formation of mucous cysts. The author suggests that the traumatized mucous islands that are retained may present abnormal growth and tend to form mucous cysts that can originate mucoceles (Fig. 6). Other authors, such as Montgomery, defend the use of intraoperative microscopy to assist in meticulously excising the sinus mucosa.

The nasofrontal duct⁷ (Fig. 7) is occluded with a variety of materials before the ductal mucosa is removed (Fig. 8). The coronal approach used to manage these pathologies makes it easier to obtain autologous bone as a suitable material for occluding the duct.

The basic principles of the obliteration of the frontal sinus have been developed over the last 50 years. This procedure has become one of the key points in the treatment of fractures, chronic infections, and benign neoplastic processes of the frontal sinus. It reduces the risk of the occurrence of infectious complications (mucocele, mucopyocele, osteomyelitis, meningitis, and cerebral abscess), which is important because of the potential for cystic degeneration of the sinus mucosa.

One of the issues in the management of the frontal sinus has centered traditionally on the material used to fill the sinus cavity after treating the underlying pathology.

Experimental and clinical studies in the literature defend the use of certain materials to fill the cavity.⁸ However, most of these studies have been made on frontal sinuses without associated pathology (animal models).

Obliteration of the frontal sinus is defined as the occupation of the frontal sinus air cavity while maintaining the bone walls intact. It is used to manage traumatic, infectious, or tumoral pathology and in the treatment of pathologic sequelae. The goal is to annul the sinus as a functional unit by impeding the regeneration of the sinus epithelium.

Our surgical team recommends filling the sinus with skull bone shavings. This procedure is facilitated by the coronal approach (Figs. 9, 10).⁹ It also allows close long-term radiologic control to be conducted as it is easier to diagnose possible recurrences of the underlying pathology (Fig. 11). After sinus obliteration, the frontal bone flap was repositioned and attached in the initially predetermined position. Osteosynthesis is usually performed with titanium, although resorbible osteosynthetic material may be used (Fig. 12).

Primary reconstruction is imperative in these procedures to ensure survival. The ideal reconstructive method minimizes the number of complications, does not interfere with postoperative follow-up imaging studies, and produces an optimal aesthetic and functional outcome.

The subcranial approach consists of an extracranial access and was described initially by Joram Raveh in 1978 for the treatment of complex injuries of the anterior skull base.^10,11 Osteotomy of the frontonasal segment can be extended purposefully toward the frontozygomatic suture depending on the needs of each case.¹² The subcranial approach facilitates the correct extracranial repair of fractures of the anterior skull base, even with dural tears and cerebral herniation. It allows the skull base to be reconstructed after the repair of dural tears with minimum retraction of the frontal lobes. It is versatile and relatively simple technically.

The main indications of the anterior subcranial approach are:

1. Complex craniofacial trauma with fractures of the skull base, dural perforations, and fractures with displacement of the fronto-naso-ethmoido-orbital complex.¹³

2. Reconstructive procedures of the skull base in cases of posttraumatic, postoperative, or idiopathic CSF fistula.

3. Decompression of the optic nerve after radical ethmoidectomy.

4. Neoplasms of the nasal cavity, nasopharynx, paranasal sinuses, orbit, or meninges with involvement of the anterior cranial fossa.¹⁴

The advantages of the anterior subcranial access include:

1. In most cases, early craniofacial reconstruction in a single surgical act (first 24-48 hours) despite concomitant severe affectation of the skull base, the presence of displaced cranial fragments, contusion, edema cerebral, and herniation of the brain tissue.

2. Significant reduction of associated morbidity, avoiding retraction of the frontal lobes, damage to the olfactory filaments, and reducing cerebral edema and postoperative recurrent CSF fistulas, together with excellent exposure of the nasal cavity, orbits, ethmoid, and sphenoid sinus (anterior cranial fossa).

3. The treatment of pseudohypertelorism (canthal symmetrical centripetal compression for the management of telecanthus), optic nerve decompression (after radical ethmoidectomy), and meticulous repair of the middle third of the face can be performed in a single surgical intervention.

4. Leak-proof seal of dural tears and management of the skull base through the paranasal spaces. It allows strict isolation of the CNS with a low rate of occurrence of CSF fistulas and epidural infections, thus reducing hospitalization time.

5. It is an aesthetically acceptable procedure that avoids facial incisions; the only incision is bicoronal, preferably camouflaged behind the hairline.

6. In trauma with fronto-naso-orbital fractures that involve the skull base, frontal contusion, high intracranial pressure and/or CSF fistula, intracranial repair using traditional approaches is possible only after resolution of the concomitant brain edema, which allows the frontal lobes to be retracted. This usually entails a delay in the initial surgical procedure of 2-3 weeks. The disadvantages of this delay are an increase in the rate of postoperative infections, interposition of granulation tissue in the fracture foci, and inadequate drainage of sinus cavities. The subcranial approach allows early surgical correction of these complex injuries in a single intervention despite involvement of the neurocranium.

Contraindications for using the subcranial approach are skull base injuries anterolateral to the orbital roof or lesions that require neurosurgical access to the frontal lobe by conventional craniotomy. The lateral limits of the approach include the optic nerves and cavernous sinuses, and the caudal limits are the lateral and lower portions of the upper maxilla.

 

Conclusions

The surgical refinements to the anterior subcranial approach that have been developed throughout its history have made it possible to successfully fulfill the following basic criteria for surgery of the skull base:

1. Ample exposure of dural defects.

2. Access for associated treatment of intracranial lesions.

3. Minimum surgical morbidity.

4. Preservation of the olfactory tracts.

5. Use of facial air spaces and safe mobilization of the craniofacial bones as an approach to the skull base.¹⁵ Obliteration of the frontal sinus.

6. Maximum respect for the neurovascular pedicles, which are crucial for the vitality of the flaps used in reconstruction and the viability of bone grafts.

7. Combined planning of the approach and reconstruction ensure effective isolation of the different cavities involved, particularly the subdural space and upper airway and digestive tract.

On the other hand, when choosing the most appropriate approach it is essential to consider the experience of the surgical team and the possibility of future operations in the same surgical field.

 

 

Correspondence:
Ignacio Zubillaga Rodríguez.
Servicio de Cirugía Oral y Maxilofacial.
Hospital Universitario 12 de Octubre.
Avda. de Córdoba s/n
28041. Madrid. España
e-mail: ignaciozubillaga@yahoo.es

Received: 27.11.07
Accepted: 17.12.08

 

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