Endoscopic endonasal skull base surgical techniques, initially developed in adult patients, are being utilized with increasing frequency in pediatric patients to treat sinonasal and skull base lesions. This article reviews the current state of endoscopic endonasal approaches to the skull base to both treat disease and reconstruct the skull base in pediatric patients. Sinonasal and skull base embryology and anatomy are reviewed as a foundation for understanding the disease processes and surgical techniques. Selected skull base pathologies and conditions that involve the pediatric skull base are also reviewed.
Key points
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Endoscopic endonasal approaches to the skull base can be used safely to manage sinonasal and skull base lesions in pediatric patients.
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Understanding the age-dependent pneumatization patterns of the paranasal sinuses, particularly the sphenoid sinus, is critical for planning a safe endonasal approach in pediatric patients.
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Techniques to minimize and control intraoperative blood loss are critical in pediatric patients owing to their overall lower blood volume compared with adult patients.
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The potential size of a nasoseptal flap is smaller in pediatric patients, and careful preoperative and intraoperative planning helps to ensure the appropriateness of its use for skull base reconstruction.
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Teamwork, surgeon experience, and surgical navigation are all important for safe and effective pediatric endoscopic skull base surgery.
Introduction
Pediatric sinonasal and skull base lesions encompass a diverse range of pathologies and conditions that have a myriad of presentations, depending on the child’s age, location of the lesion, and disease-specific characteristics. The diagnosis and management of these lesions can be complex and demands an understanding of sinonasal and skull base embryology, developmental anatomy, location-specific symptoms, and disease-specific characteristics and behavior. Comprehensive and safe management of these lesions requires a team approach of medical and surgical services with extensive training and experience. Surgical management in particular demands extensive clinical training supplemented by cadaveric dissection to gain the requisite knowledge of the 3-dimensional anatomy, specialized instrumentation, and teamwork necessary for optimal outcomes and safety.
Historically, skull base surgery was only performed by open, external approaches and craniotomies to reach various areas of the cranial base. These procedures are well-described, have a role in contemporary surgery, and have been safely performed in adult and pediatric patients. Transnasal approaches to the skull base developed later, using a microscope for visualization and driven largely by advances with pituitary surgery. More recently, endoscopic endonasal approaches (EEAs) to the skull base have developed, driven partially by advances in instrumentation and experience related to endoscopic sinus surgery and pituitary surgery.
EEAs to the skull base, initially employed for adult pituitary surgery, are now also used to safely approach varied pathologies in more distant skull base locations in the coronal and sagittal planes. As technology, instrumentation, and surgeon experience have progressed, endoscopic endonasal techniques are being used more often in pediatric skull base surgery, as demonstrated by the increasing number of publications on this topic related to pediatric patients as case reports and even some case series. This review aims to illustrate the current state of diagnosis and management of pediatric sinonasal and skull base lesions, particularly related to EEAs, resection, and reconstruction.
Introduction
Pediatric sinonasal and skull base lesions encompass a diverse range of pathologies and conditions that have a myriad of presentations, depending on the child’s age, location of the lesion, and disease-specific characteristics. The diagnosis and management of these lesions can be complex and demands an understanding of sinonasal and skull base embryology, developmental anatomy, location-specific symptoms, and disease-specific characteristics and behavior. Comprehensive and safe management of these lesions requires a team approach of medical and surgical services with extensive training and experience. Surgical management in particular demands extensive clinical training supplemented by cadaveric dissection to gain the requisite knowledge of the 3-dimensional anatomy, specialized instrumentation, and teamwork necessary for optimal outcomes and safety.
Historically, skull base surgery was only performed by open, external approaches and craniotomies to reach various areas of the cranial base. These procedures are well-described, have a role in contemporary surgery, and have been safely performed in adult and pediatric patients. Transnasal approaches to the skull base developed later, using a microscope for visualization and driven largely by advances with pituitary surgery. More recently, endoscopic endonasal approaches (EEAs) to the skull base have developed, driven partially by advances in instrumentation and experience related to endoscopic sinus surgery and pituitary surgery.
EEAs to the skull base, initially employed for adult pituitary surgery, are now also used to safely approach varied pathologies in more distant skull base locations in the coronal and sagittal planes. As technology, instrumentation, and surgeon experience have progressed, endoscopic endonasal techniques are being used more often in pediatric skull base surgery, as demonstrated by the increasing number of publications on this topic related to pediatric patients as case reports and even some case series. This review aims to illustrate the current state of diagnosis and management of pediatric sinonasal and skull base lesions, particularly related to EEAs, resection, and reconstruction.
Embryology and development
A working knowledge of sinonasal and skull base embryology is important for understanding how this complex anatomy forms leading up to birth, and serves as a basis for understanding how this anatomy grows and develops from birth to adulthood. Errors in normal embryologic development lead to some of the pathologies encountered by the skull base surgeon. Descriptions of the embryologic basis of specific lesions are discussed later in the section detailing individual lesions and pathologies. Although some important aspects are described herein, more detailed descriptions of sinonasal and skull base embryology are well-documented elsewhere.
Sinonasal Embryology and Development
The pneumatized paranasal sinuses can provide access to the skull base when performing an EEA. An understanding of the age-dependent growth and pneumatization patterns are critical to safe surgical planning.
In the fourth week of gestation, ectoderm from the frontonasal process contributes to the nasal capsule. The lateral walls of the nasal capsule enlarge, grooves begin to form, and by 9 to 10 weeks gestation, 6 ridges or ethmoturbinals are evident. The first through fourth ethmoturbinals form the uncinate process, portions of the ethmoid bulla, attachment of the middle turbinate to the lateral nasal wall, and attachment of the superior turbinate to the lateral nasal wall, respectively. The fifth and sixth ethmoturbinals obliterate or contribute to a supreme turbinate. The furrow between the first and second ethmoturbinal contributes to the ethmoid infundibulum.
The maxillary sinus begins development around 9 to 10 weeks gestation as a lateral outgrowth from the ethmoid infundibulum, is present at birth, and shows a biphasic growth pattern with increased growth between 0 to 3 years and 6 to 12 years of life. It reaches full adult size around age 18 years. The ethmoid sinuses begin development shortly after the maxillary sinuses, first with the anterior cells as evaginations from the nasal wall in the middle meatus and later the posterior cells as evaginations from the nasal wall in the superior meatus. The ethmoid sinus is present at birth, and growth and pneumatization continue until around the age of 12 years. The frontal sinus begins development around the fourth month of gestation as an upward extension from the frontal recess. Not notable at birth, the frontal sinus can been seen on x-ray at age 2 years, invades the frontal bone around 5 years, and reaches an adult size in late adolescence.
The sphenoid sinus plays a central role both physically and conceptually when planning and executing EEAs to the skull base. Most such approaches begin with a bilateral wide sphenoidotomy and identification of key landmarks within the sphenoid sinus. Around the fourth week of gestation, the sphenoid sinus begins development as paired evaginations from the sphenoethmoidal recess. Pneumatization begins at the anterior inferior sphenoid face and proceeds posteriorly well into adolescence. A recent study showed that by age 6 to 7 years, the sphenoid face is fully pneumatized and the planum sphenoidale is nearly 90% pneumatized. Pneumatization into the clival recess was seen at age 10 years, but the majority of specimens (84%) showed no dorsum sellae pneumatization. A “sellar” type pneumatization pattern was characteristic of 6- to 13-year-olds.
Skull Base Embryology and Development
The human skull develops from 3 components: The membranous neurocranium that forms the flat bones of the skull, the cartilaginous neurocranium or chondrocranium that forms the majority of the skull base, and the viscerocranium that forms the facial skeleton. Around the fourth month of gestation, the skull base begins development from the chondrocranium. The anterior and posterior skull base develops from embryologically distinct tissues. Separated by the sella turcica, the anterior skull base arises from neural crest cells, and the posterior skull base develops from the paraxial mesoderm. The anterior skull base serves as a scaffold for the facial skeleton and grows at a faster rate than the posterior skull base. Surgery of the skull base has the potential to impact craniofacial growth and development.
Surgical anatomy
A thorough understanding of the 3-dimensional sinonasal and skull base anatomy is critical for performing safe surgery. This knowledge is gained from extensive study of pictures, models, and cadaveric dissection, as well as surgical experience. The skull base is divided into 3 parts by bony landmarks on the cranial side ( Fig. 1 )—anterior, middle, and posterior—and each part is related to cranial and extracranial components ( Table 1 ). The nasal side of the skull base is better subdivided based on sinonasal landmarks and surgical modules in the sagittal and coronal planes.
| Component | Anterior Skull Base | Middle Skull Base | Posterior Skull Base |
|---|---|---|---|
| Intracranial | Anterior cranial fossa, frontal lobes | Middle cranial fossa, temporal lobes, pituitary fossa, cavernous sinuses | Posterior cranial fossa, brainstem, cerebellum |
| Osteology | Frontal bone, ethmoid bone, sphenoid bone (planum sphenoidale) | Sphenoid bone, temporal bones | Sphenoid bone, temporal bones, occipital bone |
| Foramina | Optic canal, foramen cecum, olfactory foramina, ethmoid foramina | Vidian canal, foramen rotundum, foramen ovale, foramen spinosum, internal auditory canal | Hypoglossal canal, foramen magnum, jugular foramen |
| Extracranial | Frontal and ethmoid sinuses, nasal cavity, orbit, lacrimal apparatus | Sphenoid and maxillary sinuses, nasopharynx, fossa of Rosenmueller, pterygopalatine fossa, infratemporal fossa, parapharyngeal space, infrapetrosal space | Nasopharynx |
| Major vessels | Anterior and posterior ethmoid arteries, ophthalmic artery, fronto-orbital artery, anterior cerebral artery, anterior communicating artery, artery of Heubner | Middle cerebral artery, internal carotid artery, hypophyseal arteries, Vidian artery, internal maxillary artery, sphenopalatine artery, middle meningeal artery, accessory meningeal artery | Vertebral artery, basilar artery, superior cerebellar artery, posterior cerebral artery |
| Major nerves | Olfactory bulb, olfactory tract (Cranial nerve I) | Cranial nerves II, III, IV, V, and VI; cavernous sinus nerves; Vidian nerve | Cranial nerves IX, X, XI, and XII |
It is important to understand the anatomy from both the cranial and endonasal viewpoints, and to be able to conceptualize the anatomic structure of both sides (cranial and endonasal) when viewing from one side of the skull base. For example, when viewing the cribriform plate endonasally, one must recognize that the frontal lobe and olfactory tract lie on the cranial side.
Anterior cranial base
Cranial Aspect
The anterior cranial base is composed of the frontal, ethmoid, and sphenoid bones. From anterior to posterior, it extends from the inner surface of the frontal bones to the sphenoid ridges, which are joined medially by the chiasmatic groove. The optic canal is formed by the orbital process of the frontal bone and lesser wing of the sphenoid bone and transmits the optic nerve and ophthalmic artery.
In the midline from anterior to posterior, the frontal bone, ethmoid bone, and sphenoid bones are joined at suture lines. The ethmoid bone from medial to lateral includes the crista galli, cribriform plate, and fovea ethmoidalis (ethmoid roof). More laterally, the frontal bone forms the majority of the anterior cranial base. The frontal lobes of the brain fill the anterior cranial fossa with the rectus gyri medially and the orbital gyri laterally. The frontoorbital artery lies on the inferior medial surface of the frontal lobe, and the olfactory bulb and tract lie on the cribriform plate opposing the frontal lobe’s inferior surface. The falx cerebri separates the cerebral hemispheres and attaches to the crista galli. The superior sagittal sinus runs along the superior edge of the falx cerebri and connects to an emissary vein at the foramen cecum just anterior to the crista galli.
Endonasal Aspect
From an endonasal perspective, the anterior two thirds of the midline anterior cranial base relates to the ethmoid bone and sinus (cribriform plate, fovea ethmoidalis) and the posterior one third relates to the sphenoid sinus and planum sphenoidale. The anterior ethmoid foramen transmits the anterior ethmoid artery in a lateral course just caudal to where the anterior cranial base curves superiorly into the frontal sinus. At times, this artery can be found away from the skull base on a bony mesentery, placing it at risk of injury during surgery. The posterior ethmoid foramen, often located at the junction of the fovea ethmoidalis and planum sphenoidale, transmits the posterior ethmoid artery. Both anterior and posterior ethmoid arteries are branches of the ophthalmic artery, and both foramina are within the frontoethmoid suture.
Middle cranial base
Cranial Aspect
The middle cranial base is composed of the sphenoid and temporal bones. From anterior to posterior, it extends from the sphenoid ridges and chiasmatic groove to the petrous ridges and dorsum sellae. The medial region is largely composed of the body of the sphenoid bone and includes the sella turcica. The sella turcica includes, from anterior to posterior, the tuberculum sellae, anterior clinoid processes, hypophyseal fossa (housing the pituitary gland), and dorsum sellae with posterior clinoid processes. The cavernous sinus, a venous channel, lies immediately lateral to each side of the sella turcica and transmits the cavernous segment of the carotid artery and cranial nerves III, IV, V1, and VI. The temporal lobes of the brain fill the middle cranial fossae.
More laterally, the middle fossa transmits the other branches of the trigeminal nerves through foramen rotundum and foramen ovale. The middle meningeal artery enters via foramen spinosum. The floor of the middle fossa overlies the horizontal petrous internal carotid artery and contains the geniculate ganglion with its exposed greater superficial petrosal nerve branch which extends over the horizontal internal carotid artery to the vidian nerve.
Endonasal Aspect
The undersurface of the middle cranial base relates to the following 4 defined spaces: Pterygopalatine fossa, infratemporal fossa, parapharyngeal space, and infrapetrosal space. These spaces are dense with important structures and many neurovascular elements that traverse the skull base via foramina. The detailed boundaries and contents of these spaces are described elsewhere and are beyond the scope of this article. From an endoscopic endonasal perspective, the pterygopalatine fossa and infratemporal fossa are more approachable, often after removal of the medial and posterior maxillary sinus walls. From the nasal cavity a natural pathway can be followed laterally through the sphenopalatine foramen to the pterygopalatine fossa, and then further lateral through the pterygomaxillary fissure to the infratemporal fossa. Within the sphenoid sinus, the anterior face of the hypophyseal fossa can be easily seen with sufficient sinus pneumatization.
Posterior cranial base
Cranial Aspect
The posterior cranial base is composed of the sphenoid, temporal, and occipital bones. From anterior to posterior, it extends from the petrous ridges and dorsum sellae to the inner surface of the occipital bone. The posterior cranial fossa is the most inferiorly located fossa, lies between the tentorium cerebelli and foramen magnum, and houses the brainstem and cerebellum. The internal acoustic meatus transmits cranial nerves VII and VIII, the jugular foramen transmits the internal jugular vein and cranial nerves IX, X, and XI, and the hypoglossal canal transmits cranial nerve XII.
Endonasal Aspect
From an endonasal perspective the posterior cranial base relates to the clivus and can be divided into 3 segments :
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Superior segment from the dorsum sellae and posterior clinoids to the sellar floor;
- 2.
Middle segment from the sellar floor to the sphenoid sinus floor (clival recess); and
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Inferior segment from the sphenoid sinus floor to the foramen magnum.
The superior segment relates intracranially with cranial nerve III, the posterior cerebral artery, and the superior cerebellar artery; the middle segment relates to cranial nerve VI, the anterior inferior cerebellar artery, and the basilar artery; and the inferior segment relates to cranial nerves IX, X, and XII and the vertebrobasilar junction.
Sphenoid sinus anatomy
The endonasal anatomy of the sphenoid sinus deserves emphasis owing to the central role it plays in planning and executing endonasal skull base surgery. The majority of EEAs begin with a wide bilateral sphenoidotomy (removal of the sphenoid face from planum to floor and laterally to each lateral recess, the sphenoid rostrum, and the intersinus septations) and identification of anatomic landmarks. A completely pneumatized sphenoid sinus (late adolescent or adult) often will have the following endoscopic landmarks:
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Midline from superior to inferior: Planum sphenoidale, tuberculum sellae, sellar floor, clival recess; and
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Laterally from superior to inferior: Optic canal, lateral opticocarotid recess, parasellar carotid artery, paraclival carotid artery ( Fig. 2 ).
Fig. 2
This cadaveric dissection demonstrates an endoscopic endonasal view of important skull base landmarks and anatomy seen after wide bilateral sphenoidectomy. lOCR, lateral opticocarotid recess; LR, lateral recess; MC, middle clinoid; mOCR, medial opticocarotid recess; ON, optic nerve; pcICA, paraclival internal carotid artery; psICA, parasellar internal carotid artery.
The lateral opticocarotid recess is a pneumatization of the optic strut, a strip of bone on the cranial side that separates the optic nerve and superior orbital fissure, extending to the sphenoid sinus from the anterior clinoid process.
Understanding the age-dependent progression of sphenoid sinus pneumatization is critical when performing surgery in pediatric patients. Many of the endoscopic landmarks notable with complete pneumatization can be difficult or impossible to visualize upon initially entering the sinus in young patients with incomplete pneumatization. Surgeon experience, surgical navigation, and careful bone removal are essential when identifying sphenoid anatomy in an incompletely pneumatized sinus. An appropriate understanding of the related anatomy, combined with accurate image guidance and careful exposure allows for efficient identification of critical structures, regardless of degree of pneumatization.
Special anatomic considerations for pediatric skull base surgery
Along with variable sphenoid sinus pneumatization, the smaller size of the pediatric sinonasal anatomy can pose limitations on the ability to approach the skull base endonasally. Until the age of 6 to 7, the nasal aperture is significantly narrower compared with that in adults and may pose limitations for an EEA in very young patients. Further, intercarotid artery distances within the clivus at the level of the cavernous sinus are statistically narrower in children relative to adults. More inferiorly, intercarotid artery distances at the level of the superior clivus are stable throughout life. Knowledge of the anatomic location of sinonasal and skull base growth centers is important, because disturbance of these centers can impact craniofacial growth. For example, the spheno-occipital synchondrosis is among the primary skull base growth centers and closes at the completion of skull base ossification around age 12 to 16 years.
Surgical technique: approach and resection
Pediatric skull base surgery has a rich history. Over the last several decades, various approaches and techniques have been described and mastered by surgeons to address pathology in essentially any skull base location. Initially described in adults, application of skull base approaches to pediatric patients are first found in the literature from the 1980s and 1990s. Open surgical approaches, both transfacial (craniofacial) and transcranial (bifrontal, frontotemporal, orbitozygomatic, lateral temporal, preauricular infratemporal, retrosigmoid, suboccipital, transmastoid, translabyrinthine, etc) are well-described and used in contemporary surgery. In the 1990s, microscopic transnasal transsphenoidal approaches were popularized and are still in use currently. The focus of this article is on the more recent developments with EEAs to the skull base in the pediatric population.
Endoscopic Skull Base Surgery: The Sagittal and Coronal Planes
Approaches to the skull base from the endoscopic endonasal perspective can be categorized by individual surgical modules as first described by the University of Pittsburgh Center for Cranial Base Surgery ( Table 2 ). The modules are described by the named portion of the skull base that serves as the site of operation or point of entry into the intracranial cavity.
