Anterior cranial fossa encephaloceles (sincipital) are congenital herniations of intracerebral contents from the anterior cranial fossa through a defect in the facial skeleton. The contents may be comprised of meninges alone (meningocele), meninges and brain (meningoencephalocele), or may also include part of a ventricle (hydroencephalomeningocele). These anomalies have been subdivided into frontoethmoidal encephaloceles, interfrontal encephaloceles, and those encephaloceles associated with rare craniofacial clefts. Frontoethmoidal encephaloceles are herniations of the intracranial contents through a defect in the skull at the junction of the frontal and ethmoidal bones. They can be classified further as nasofrontal (between the nasal and the frontal bones), nasoethmoidal (between the nasal bones and the nasal cartilage), or naso-orbital (through the medial wall of the orbit). 1 There can be combinations and multiples of these subclassifications (see Case 2).
The goals of correction include
- Urgent closure of open skin defects to prevent infection and desiccation of viable brain tissue. This includes the early removal of nonviable tissue (Case 3), and early prevention of rupture of a thin meningoencephalocele sac.
- Removal or invagination of nonfunctional extracranial cerebral tissue with water-tight closure of the dura
- Total craniofacial reconstruction with particular emphasis on exact skeletal reconstruction, especially avoiding the “long-nose deformity”
We review our experience at the Melbourne Craniofacial Unit and discuss our evolution toward a definitive, single-stage correction, including refinements.
Patients and Methods
The records of all cases of anterior cranial fossa encephaloceles treated at our institution since January 1, 1971, were reviewed. There were 35 patients with frontoethmoidal tumors treated during this period. A Filemaker Pro database program (Apple, Version 4.1, Santa Clara, CA) was written to collect the following information: diagnosis, extent of encephalocele, vision, procedures, intraoperative data, bone grafts, complications, and secondary procedures. On reviewing these 35 patients, 12 were patients with sincipital encephaloceles with complete records, allowing study of intraoperative events, complications, and subsequent procedures.
The diagnosis is usually clinical. Although any mass in the area may mimic an encephalocele, the most common differential diagnosis is a dermoid cyst or a glioma. Some would regard the latter as ectopic central nervous system tissue excluded during embryological fusion of the cranium. Hemangiomas of the glabella, nasal, and orbital areas may also present confusion in diagnosis.
Usually the diagnosis is obvious, especially if there is clinical or palpable cerebral pulsation. Plain skull and facial radiographs can help delineate the size and position of the cranial defect through which the herniation passes. Encephaloceles can often be associated with other central nervous system abnormalities, in particular hydrocephalus. Ultrasound may be helpful in determining ventricular size, but ultimately computed tomographic (CT) scans with appropriate brain windows and three-dimensional reconstruction give the best assessment of the diagnosis and pathological anatomy. These scans are integral to surgical planning. Usually, surgical correction is an elective event, but open meningoencephaloceles (especially with necrotic or infarcted material) require urgent intervention to prevent infection or death.
The surgical approach is usually a combination of transcranial and direct anterior incisions. The skin overlying encephaloceles is often abnormal, with thinning rugosities, scattered adnexal structures, and diverse pigmentation (see Cases 1, 3, 4, and 5). All attempts are made to design an approach that will remove the abnormal skin. When possible, vertical midline scars do very well (Case 5), and Z-plasties are avoided because they are extremely noticeable in the long term. More often, the normal nasal skin is better preserved using paranasal incisions, which extend into the supratarsal fold of the upper eyelid and are connected with a transverse incision at the radix (Cases 1 and 2). This usually gives a better longstanding result and helps lower the raised eyebrows, which are commonly seen with frontoethmoidal encephaloceles. As far as the transcranial approach is concerned, our preference is now a wavy or broken bicoronal incision designed to make the scar less obvious when the hair is short, curly, or wet.
Incisions are planned to place the resulting scars in the borders of cosmetic facial units. Transcolumellar open rhinoplasty may also be used to gain additional exposure. This is particularly useful if there is an intranasal component of the encephalocele, and is also useful so that a definitive aesthetic nasal tip can be sculpted when the nose is being reconstructed with bone and/or cartilage.
Dealing With the Central Nervous System Herniation
The dura overlying encephaloceles is usually clinically different from normal dura. It is usually thinner and more irregular, and probably lacks osteogenic potential in that there is no sign of bone formation over the surface. With smaller encephaloceles, the sac and abnormal dura can be invaginated surgically, and the normal dura approximated and sutured. With larger encephaloceles, excision of the sac with a water-tight closure is recommended. The contents of the sac are usually disorganized neuroglial tissues with no functional importance. Double breasting the dura, or using a graft of temporal fascia or periosteum can often achieve a good seal. The reduction of the sac can induce subsequent raised intracranial pressure even in patients in whom the cranial vault is enlarged to accommodate the increased volume. The reasons for this remain unclear but are probably related to alterations in the dynamics of cerebrospinal fluid flow.
The principle of isolating the neck of the sac is important, and this often requires removal of bone. A bifrontal craniotomy is usually performed, but the design has to be preplanned so that it will not interfere with or make difficult the subsequent skeletal deformity correction.
The skeletal deformity with frontoethmoidal encephaloceles obviously varies with the type of encephalocele and the severity (see Case 1, Figures 1A–1E). Nasoethmoidal encephaloceles herniate through the foramen cecum between the nasal bones and the nasal cartilage, and involve the ethmoid complex. The encephalocele may cause a secondary nasal cleft that mimics a 0–14 Tessier cleft and leads to a short-nose deformity after correction (Case 5). The floor of the anterior cranial fossa tends to be steep and cone shaped, and because there is a relatively long canal from the skull to the face, transcranial repair is advised.
Nasofrontal encephaloceles involve a hernia from the foramen cecum to the junction of the nasal and frontal bones, with the nasal bones being intact at the inferior margin of the defect. With the nasofrontal type, the cribriform plate and base of the nose are usually depressed, leading to a long midface, depending on the age of the patient. We think that because of the short canal involved in this type, an extracranial transfacial repair is occasionally possible, which may be an attractive option in countries or areas where craniofacial expertise may not be available. The differentiation between these two types can be made clinically, and with skull and facial radiographs.
Naso-orbital encephaloceles occur less commonly and involve a defect in the medial wall of the orbit and a tract through a bony tunnel from the anterior fossa to the orbit with intact nasal bones. One or both eyes may be depressed vertically, demonstrating skeletal orbital dystopia (Cases 2 and 4).
In nearly all patients with frontoethmoidal encephaloceles, the medial orbital walls are widened but the lateral orbital walls are usually in the normal position. Hence the term interorbital hypertelorism gives a better description of the skeletal deformity (rather than true orbital hypertelorism, also known as teleorbitism).
Associated with these skeletal deformities, there is often downward displacement of the canthi and upward elevation of the eyebrows (Cases 1 and 4).
An accurate appreciation of the skeletal anatomy is essential for correction. If the interorbital hypertelorism alone is corrected in the presence of a long midface, then when the nose is reconstructed the patient will end up with long-nose deformity. 2
The appearance of the long-nose deformity or long-nose hypertelorism cannot be improved if the trigonocephaly and elevation of the supraorbital rims are not addressed. Jackson and colleagues 2 have described the correction of interorbital hypertelorism accompanied by elevation of the nasal bridge and cribriform plate as a method of avoiding the deformity.
Our treatment of interorbital hypertelorism and trigonocephaly involves separating each supraorbital rim and medial orbital wall complex, including that part of the anterior cranial fossa adjacent to the exiting foramen of the encephalocele (see Figs 2B–2F). Once the encephalocele has been reduced, these segments are moved in three dimensions by rotating medially, downward, and posteriorly in the midline, thus lowering the supraorbital rims, shortening the midface, and correcting the trigonocephalic bulge with one movement. The upper part of the lateral orbital rims moves anteriorly in exactly the same way as a standard trigonocephalic correction in an infant (see Fig 2). With these bony movements, the retained pieces of anterior cranial fossa will also move medially and close the defect. The frontal bone will need to be remodeled to eliminate its trigonocephalic bulge (Case 1) or will need to be replaced with a new split cranial forehead taken from another area (Case 2, Figs 3C and 3D). The Marchac template has been very valuable in planning these movements at operation (Case 2, Fig 3C). If inadequate skeletal corrections have already been done in the past and the patient is mature, the long nose/long face can be corrected with nasal shortening and maxillary (Le Fort I) impaction.
Nasal reconstruction is performed as part of the primary procedure. Cranial bone or, more commonly, costochondral grafts are used to provide appropriate nasal shape and support. Our preference for costochondral grafts in this region stems from the fact that the lower alar cartilages can be supported accurately by the chondral element, thereby giving an aesthetic nasal tip that is not overly rigid. The fashioning of the tip is usually facilitated by an open rhinoplasty approach. The bone graft itself is fixed rigidly to the glabellar region with internal fixation. The upper lateral cartilages are connected to the lateral side of the graft so that the graft acts as a spreader or spacer that prevents dysfunction of the nasal valves. The tip cartilages are elevated and connected to the end of the graft to give adequate projection and shape (Fig 2H).
After completion of the skeletal framework, the medial canthal ligaments are isolated, looped, and transfixed with 30-gauge wire. Canthopexies are performed at the appropriate level, usually by joining the wires across the midline. Care is taken to protect the lacrimal apparatus, and this can be cannulated temporarily when necessary to help during the operative procedure.
Historically, our unit has used wire and miniplate fixation with good results. More recently, resorbable plates have been used. Although resorbable plating has obvious advantages for use in the pediatric patient, the ultimate role for resorbable plates used for osteosynthesis has yet to be elucidated completely.
Nasofrontal encephaloceles were present in 6 of the 12 patients: nasoethmoidal (N = 3), naso-orbital (N = 1), and combined defects (N = 3). Secondary rhinoplasties were required in five patients. One patient required two revision rhinoplasty procedures and one patient required four revision procedures. Increased intracranial pressure occurred in two patients after surgery and required subsequent shunting procedures. One patient had a recurrent medial canthal infection that required two debridement procedures and removal of the medial canthal wire. One patient had a recurrent/chronic infection of the calvarial bone used for the initial nasal repair, which subsequently required removal and revision with rib graft. Calvarial bone was used for nasal reconstruction in six patients, costochondral graft in three patients, and both were required in three patients.
Encephaloceles are subdivided into the following categories: occipital, basal, convexity, and sincipital (anterior). 3 Suwanwela and Suwanwela 1 have subdivided the sincipital group further into frontoethmoidal encephaloceles, interfrontal encephaloceles, and those encephaloceles associated with craniofacial clefts. The frontoethmoidal group is subdivided further into nasofrontal, nasoethmoidal, and naso-orbital types. 1 Encephaloceles occur in 1 per 5,000 births worldwide. 3 The incidence of sincipital encephalocele compared with occipital encephalocele is substantially greater in the tropical latitudes, particularly in parts of Asia and Africa, and is also more common in parts of Russia. 3 However, the occipital-to-sincipital encephalomeningocele ratio is reversed in North America, Australia, Europe, and parts of South America, and varies from 2.5:1 to 15:1. 3 The occipital encephaloceles occur in 1 to 3 per 10,000 live births. 4 The etiology of sincipital encephalocele is unknown but includes ethnic, genetic, and environmental factors and paternal age. 5,6 Sincipital encephaloceles are usually the result of a herniation of the intracranial contents through a midline tunnel from the anterior cranial fossa into the facial skeleton. If the skeletal defect is associated specifically with a Tessier craniofacial cleft, then the encephalocele is thought to be secondary to the cleft and is classified as such. The exit opening in the cranium is cleft shaped, rather than circular, and there are other obvious soft-tissue signs to diagnose the cleft.
With frontoethmoidal encephaloceles, the defect is usually found at the foramen cecum, which is normally a small pit in the frontal bone anterior to the crista galli to which the falx cerebri attaches. The sincipital encephalocele, particularly frontoethmoidal, may be associated with craniofacial deformity consisting of interorbital hypertelorism (rarely true orbital hypertelorism), secondary trigonocephaly, orbital dystopia, elongation of the face, nasal deformity, and dental malocclusion. 2
The diagnosis, examination, and operative procedure have been already discussed, but several issues warrant special attention, and are addressed in the following paragraphs.
Ortiz–Monasterio and Fuente del Campo 7 first coined the term long-nose deformity. Jackson and colleagues 2 also discussed this issue in 1983. Facial and nasal elongation is partly the result of depression of the cribiform plate and the nasal placode. Without proper management, nasal elongation is actually more obvious after repair and reduction of the encephalocele. This is readily apparent in case reports in the literature in which the long nose and midface are not addressed at the time of operative repair. 8 An appropriate nose can be made out of cranial bone graft or costochondral bone graft if a good cartilaginous element is necessary. The bone graft is fixed rigidly to the glabellar region to provide cantilever support, and the upper lateral cartilages are elevated to the edge of the graft to prevent nasal obstruction. The lower alar cartilages are elevated anteriorly to the bone graft so that the tip projection is normal (see Figs 2G and 2H). If the external skin incisions do not require the tip of the nose to be exposed, then an open rhinoplasty approach at the time of reconstruction is used (Case 1). It should be noted that early nasal reconstructions are unlikely to grow, and serial augmentations and revisions may be necessary until facial growth ceases. Revision rhinoplasty procedures were necessary in five of the patients in the current series.
Our clinical impression, as well as analysis of three-dimensional CT scans and 3-dimensional models created from these scans, showed obvious trigonocephaly in nearly all patients. This is probably deformational, but may be metopic synostosis induced secondarily during development. Certainly we have not seen a patent metopic suture associated with frontoethmoidal encephaloceles, but this may merely be a reflection of our series in that not many present as infants. Operating on the models showed the simple correction of the trigonocephaly by osteotomies of the supraorbital rim, including the medial anterior cranial fossa (adjacent to the foramen cecum), and allowed the two halves of the rim to be advanced laterally and brought back medially to close the bone defect through which the encephalocele had passed (Fig 2). In addition, the supraorbital rims were rotated inferiorly and medially to lower the root of the nose and to achieve more normal facial proportions. The frontal bone, removed for access, is usually split to provide inner table bone grafts, and is then remodeled to take on a normal forehead shape. The Marchac forehead templates are usually helpful for this. If this remodeling is difficult, then a new forehead can be taken from an appropriate area of the parietal skull, and the remaining defect from the donor site can be repaired with bone grafts.
Obviously if the encephalocele is very large, the excision option is preferable to avoid raised intracranial pressure. Occasionally, removal of any encephalocele can lead to postoperative hydrocephalus. The mechanism of this is unclear, but it may be that the encephalocele contains a large part of the resorption mechanism in that particular individual. Watching for postoperative hydrocephalus is a standard part of postoperative management. Although numerous authors discuss postoperative hydrocephalus, it is unclear which prognostic indicators portend an increased likelihood of postoperative shunting. 9,10 Simpson and associates 9 reviewed 22 sincipital encephaloceles, and only four of their patients required shunting. In the current series only 2 of 12 patients required shunting.
Removal of abnormal skin is important from an aesthetic standpoint. If nasal bifidity is present (low nasofrontal or nasoethmoidal encephalocele), a midline scar is preferable without Z-plasties (Case 5). If the long-nose deformity is likely to occur, the dorsum and tip are depressed but the skin is normal inferior to the encephalocele. In these cases, placing the incisions at the borders of the nasal subunit is preferable. Brow elevation is also best addressed during the initial surgery with a reverse brow lift. This is achieved mainly by anchoring the coronal flap inferiorly to the supraorbital rim. Excess skin can be excised inferiorly in the supratarsal eyelid line (Cases 1 and 2).
Timing of Surgery
Although the timing of surgery is often beyond the control of the craniofacial unit and is dependent on when the patients present for treatment, our unit has developed the following approach.
Emergency Surgery: If the child is born with an open encephalocele, emergency closure before the development of meningitis should be performed. If the encephalocele is twisted, infarcted, or obstructing vision or the airway, it should also be addressed immediately.
Definitive bony correction is relatively easy in the infant but should be deferred for the first 4 or 5 months to lessen the risks of anesthesia and blood loss. However, the earlier the deforming stimulus of the encephalocele is removed, the less subsequent growth disturbance occurs (Cases 3, 4, and 5). Ideally, infancy is the best time for definitive correction.
Early (School Age) Surgery: This is a good time for surgery because the psychological problems related to encephaloceles can be severe. The only minor drawback is that the reconstructed nose is unlikely to grow, and the patient and their relatives need to be warned that serial augmentation may be necessary until after puberty.
Late (After Puberty) Repair: This is straightforward because growth is no longer an issue. However, the long-nose deformity and the long midface may also require correction. Quite often, a Le Fort I maxillary retrusion procedure is required, along with the definitive orbital and nose reconstructions.
The prognosis for the anterior encephalocele patient is generally good and is usually associated with normal intelligence and motor development. However, mental retardation, epilepsy, and ocular problems have been described in this group. 5 Epilepsy may develop late. When there is a gross brain herniation or when the extruded brain is damaged and gliotic, the prognosis may be poor.
The successful correction of the frontonasal encephalocele centers on the following five principles:
- Accurate diagnosis, delineation of the anatomy, and surgical planning (The type of operative repair depends on the anatomic pathology of the particular lesion and the surgical resources and equipment available.)
- Osteotomies and bone movements that correct the whole deformity, including the trigonocephalic head shape and interorbital hypertelorism
- Nasal reconstruction that avoids the long-nose deformity
- Skin closure that removes abnormal skin and places incisions in advantageous locations
- Single-stage surgery if possible, when the neurosurgical and craniofacial expertise is present