Modification of the Fetal Profile Line to Measure Reversal of Forehead Slope after Early Repair of Frontoethmoidal Encephalocele

Abstract

Objective  Congenital frontoethmoidal encephaloceles are associated with a shallow sloping forehead. We (1) sought to determine if early repair reverses abnormal forehead slope, and (2) assessed a modification of the fetal profile (FP) line to assess results.

Design  Study of two cases.

Participants  Newborns with frontoethmoidal encephaloceles repaired prior to the age of 4 months with cranial base bone grafting.

Main Outcome Measures  Forehead slope was assessed using a modification of the FP line, defined as the line that passes through the anterior border of the mandible and nasion, on pre and postoperative magnetic resonance imaging (MRI) in the midsagittal plane. A modified FP (mFP) line anterior to the forehead was “ − ”, while a posterior (normal) mFP line was “ + .” The largest distance from the mFP line to the forehead was measured.

Results  Both infants underwent bifrontal craniotomy, excision of encephalocele, and repair of cribriform plate defect using full-thickness autologous parietal bone before the age of 4 months. Preoperatively, the mFP line was −20.6 mm in case 1, and −9.8 mm in case 2. In both cases, follow-up MRI showed excellent reversal of forehead slope and normal calvarium development. The mFP line improved to +7.4 (age = 16 months) in case 1, and +7.6 (age = 11 months) in case 2. The parietal bone donor site ossified completely within 3 months in both cases.

Conclusion  Early repair with bone grafting can promote normal frontal bone development and improve forehead slope. The mFP line is a useful method to measure degree of forehead slope.

Introduction

Encephaloceles are a type of neural tube defect that occur due to incomplete separation of surface ectoderm from neural ectoderm in 4 weeks of gestation, resulting in a calvarial defect that allows herniation of intracranial contents. ¹ They are classified based on location and include occipital, sincipital (frontal, anterior, or frontoethmoidal), cranial vault, and basal. Frontoethmodal encephaloceles are further categorized by the scheme described by Suwanwela and Suwenwala into nasofrontal, nasoethmoidal, and nasoorbital lesions ^{2 3 4}

Nasofrontal encephaloceles present as a mass at the glabela between the frontal and nasal bones resulting in telecanthus and inferior displacement of the nasal bones. Nasoethmoidal lesions present as unilateral or bilateral nasal mass, often resulting in superior displacement of the nasal bones and inferior displacement of the greater alar cartilages. Nasoorbital lesions present as a mass through a defect in the medial orbital wall. ⁵ Encephaloceles can cause recurrent meningoencephalitis due to direct communication of brain parenchyma to the external environment.

Like other forms of spinal and cranial dysraphism, congenital frontoethmoidal encephaloceles are often associated with a shallow sloping forehead, thought to be secondary to abnormal development of frontal bone due to herniation of central nervous system contents elsewhere. No literature exists discussing the role of early encephalocele repair and skull base closure in restoring normal intracranial pressure, thus promoting normal frontal bone development. Moreover, no reported methods exist to measure forehead slope in infants with this condition. In a report of 257 patients with frontoethmoidal encephaloceles from Cambodia, ⁶ 14% of the children had experienced name calling, 18% refused to go to school due to perceived shame, and 29% attended school but were mocked by other children. Although they did not report on the frontal slope, 25% of these cases reported that there was an improvement in their social life following repair. Although the frontal sloping is just one portion of the deformity, its correction is certainly part of achieving a more “normal” appearance.

We report two cases of frontoethmoidal encephalocele repaired prior to the age of 4 months with autologous bone grafting of the cranial base defect, resulting in reversal of forehead sloping and normal frontal bone development, highlighting the importance of early repair. Moreover, we report a method for quantifying forehead slope, using a modification of the fetal profile (FP) line. The FP line, typically an ultrasound-based measurement, has proven to be a useful measurement of fetal facial profiles in prenatal diagnosis of Down's syndrome and other disorders, particularly at the second and third trimester of pregnancy. ^{7 8} In prior ultrasound studies, a FP line that was “zero” or “negative” was considered abnormal, and a “positive” FP line was considered normal ^{7 8} . Here, we use a modification of the FP (mFP) line measurements in the postnatal period, based on magnetic resonance images.

Case Description and Surgical Technique

Case 1

This boy was born at 37 weeks of gestation with a left nasal mass and respiratory distress requiring intubation. On exam, his head was microcephalic with a shallow sloping forehead. His left nares were enlarged with a 2 cm × 4 cm soft red membranous sac protruding. CT and magnetic resonance imaging (MRI) showed a nasoethmoidal encephalocele extending through the cribiform plate ( Fig. 1 ). The skull base defect was 2.0 cm × 0.9 cm.

Fig. 1.

Midsagittal ( A ) and 3D ( B ) CT reconstructions obtained on day of life 1 demonstrate a defect extending from the cribriform plate through the nasofrontal suture and between the frontal bones (arrows). Midsagittal T2-weighted MRI ( C ) shows a nasofrontal encephalocele, and shallow sloping forehead (block arrow). Midsagittal T2-weighted MRI obtained at age 16 months ( D ) shows repair of the encephalocele with resolution of shallow sloping forehead. 3D, three-dimensional; CT, computerized tomography; MRI, magnetic resonance imaging.

At the age of 4 weeks, the infant underwent bifrontal craniotomy, excision of encephalocele, duraplasty and repair of cribiform plate defect using a full-thickness autologous cranial bone graft harvested from the right parietal bone and secured with absorbable plates. The intranasal encephalocele was removed endoscopically after it was detached from the intracranial parenchyma.

Case 2

This boy was born at 35 weeks of gestation, with microcephaly, shallow sloping forehead, orbital hypertelorism, and a 3 cm × 3 cm skin covered mass protruding from the frontal area between the eyes, including the nasion. MRI and CT revealed a nasofrontal encephalocele protruding through a 1.5 cm × 2 cm cribriform plate defect ( Fig. 2 ). At the age of 4 months, the infant underwent bifrontal craniotomy, excision of encephalocele, duraplasty, and repair of cribriform plate defect using a full-thickness autologous cranial bone graft harvested from the right parietal bone and secured with absorbable plates similar to case 1. The subcutaneous encephalocele was excised through an open incision.

Fig. 2.

Midsagittal ( A ) and coronal ( B ) CT reconstructions obtained on day-of-life 1 demonstrate a defect in the cribriform plate (arrows). Midsagittal T2-weighted MRI ( C ) obtained on day-of-life 1 show a nasoethmoidal encephalocele and a shallow sloping forehead (block arrow). Midsagittal T2-weighted MRI (D) obtained at age 14 months reveals successful repair of encephalocele and skull base defect with autologous cranial graft, and normalization of forehead slope (block arrow). CT, computerized tomography; MRI, magnetic resonance imaging.

There were some commonalities between the surgical techniques used in these two cases. The bicoronal incision was performed in a zigzag fashion, allowing for improved scar when the hair is wet as previously has been described. ⁹ The protruding gliotic brain was removed. The dural defect was repaired with an inlay graft. A vascularized pericranial flap was used to cover the defect. A full-thickness calvarial graft was used to add support to the skull base defect repair using absorbable plates and screws.

Our methods of repair are similar to those reported in the literature. Multilayer reconstruction is a principal used not just in encephalocele repair but in skull base surgery in general. ¹⁰ There are no reports of patients having surgery below 3 months of age like patient 1 ^{11 12} This patient had respiratory difficulties from the nasal mass which is why the surgery was performed as early as possible. Regarding autologous bone graft for repair there are reports of using rib graft ¹³ , which was not necessary due to the age of the patients. Full-thickness calvarial graft in this age range can prevent the need for additional incisions for bone harvest. There are no other reports of frontoethmoidal encephalocele repair with full-thickness calvarial graft. However, this is a practice that is used in craniofacial surgery. Infants can reform bone from osteogenic and osteoinductive factors secreted from their dura and pericranium and therefore full-thickness grafting has been used previously for other pathologies. ¹⁴ Some report that this can be done for children under the age of 6 months. ¹⁵ However this concept is most well known after craniosynostosis surgery when there are defects in the skull that they fill in reliably in children under 6 months and less reliably up to 1 year. ¹⁶

Methods

Forehead sloping was assessed on preoperative and postoperative MR images using a mFP line; defined as the line that passes through the anterior border of the mandible and nasion in the midsagittal plane. A mFP line anterior to the forehead was “ − ” while a posterior mFP line was “ + .” In prior ultrasound studies, a FP line that was “0” or “ − ” was considered abnormal, and a “ + ” FP line was considered normal ^{7 8} . For the purpose of analysis of our two cases, we were consistent with this prior literature and considered a “ + ” mFP line to be normal, while a mFP line that was “0” or “ − ” was considered to be abnormal. The largest perpendicular distance from the mFP line to the forehead was measured. Forehead slope was defined as the distance of the frontal bone from the mFP line, as shown in Fig. 3 .

Fig. 3.

Method for forehead slope assessment: modification of the FP line, defined as the line that passes through the anterior border of the mandible and nasion (blue line). The FP line is negative in the case of a shallow-sloping forehead ( A ) and positive with a normal forehead slope ( B ). FP, fetal profile.

Results

In case 1, preoperatively, the mFP line was −20.6 mm. Follow-up MRI showed excellent reversal of forehead sloping and normal development of the calvarium with normalization of the mFP line to +7.4 (age = 16 months; Fig. 1 and Table 1 ). The parietal bone donor site ossified completely within 3 months and the child did not require a shunt or develop endocrinopathies.

Table 1. Fetal profile line measurements before and after encephalocele repair.

	Case 1	Case 2
Preoperative	−20.6	+7.4
Postoperative	−9.8	+7.6

In case 2, preoperatively, the mFP line was −9.8 mm. Follow-up MRI showed excellent reversal of forehead slope and normal development of the calvarium with normalization of the mFP line to +7.6 (age = 11 months; Fig. 2 and Table 1 ). The parietal bone donor site ossified completely within 3 months and the child did not require a shunt or develop endocrinopathies.

Discussion

This is the first report, to our knowledge, that uses a modification of the FP line to measure changes in forehead slope that occur after early repair of frontoethmoidal encephalocele. A prior report exists on 30 frontoethmoidal encephalocele repairs; however, the average patient age at the time of operation was 8.7 years and there was no report on the cosmetic appearance of the forehead afterward. ¹⁷ The concept of early surgery as a way to prevent dysmorphic progression is a concept, which has been discussed previously. Suwanwala amd Hongsaprabhas in 1966 first discussed the theory that progressive facial deformity may be prevented by early correction of the encephalocele. ¹⁸ Charoonsmith and Suwenwala in 1974 then suggested that only encephalocele correction is needed initially and the facial deformity would regress on its own. ¹⁹ With these defects being repaired at a time when the skull is still forming, it suggests that the improvements we have seen in these children may not be as apparent in an older population.

A review of 40 anterior encephalocele patients report that these patients that have associated structural abnormalities like corpus callosum agenesis or arachnoid cysts perform poorly in dimensions of intelligence. ^{11 20} It is not clear if early repair, as we have demonstrated, would improve any of these outcomes. Our reported patients have not undergone long-term neurocognitive assessment. Around 20% of encephalocele patients require permanent cerebrospinal fluid diversion due to hydrocephalus. ²¹ This may have some impact on neurocognitive function as well.

In addition to risk of recurrent meningoencephalitis, there is the potential for progressive deformity which can be minimized by early repair. Although we did not intend to measure rate of normalization, our reported normalization at 14 and 16 months in these two cases would suggest normalization occurs within a year in cases repaired early in life (prior to age of 4 months). Importantly, the calvarial graft prevents further descent of tissue through the defect and we feel this is crucial for subsequent development of normal frontal bone slope. Da Silva Freitas et al discuss reconstruction of calvarium following encephalocele excision ²² and split calvarial bone graft had been discussed as an option. In children, as young as in our study, a full-thickness graft can be used without any residual defect.

Pure endoscopic repair of anterior skull base defects in children has been previously described ²³ ; however, with such large bony defects as seen in our cases, a purely endoscopic approach in children this young would be difficult, particularly in the case of the nasofrontal encephalocele (case 2). Additionally, small nares in babies in the first days of life create technical challenges regarding purely endoscopic repair. However, if the bony defect could be obliterated with bone graft at such a young enough age with a purely endoscopic approach, we would hypothesize that the outcome regarding forehead slope would be similar, as we feel the two most important prognostic factors regarding normalization of forehead slope are age of repair and ability to obliterate the cribriform plate defect.

Conclusion

Here, we demonstrate that early repair of frontoethmoidal encephalocele with bone grafting can promote normal frontal bone development and improve forehead sloping. Moreover, we suggest use of a modification of the FP line as a useful method to measure degree of forehead slope. These cases suggest that early repair of the defect with a bone graft results in an excellent cosmetic result, with resolution of abnormal forehead slope. We acknowledge that we only present 2 cases, and more data are needed to determine if this is always true.