Atretic cephalocele and differential considerations: A small case series

Abstract

Any posterior midline cystic or soft tissue scalp mass in an infant needs evaluation with MRI brain and MRV brain to look for intracranial extension of the lesion. One of the differential considerations is an atretic cephalocele, which can be a difficult diagnosis, especially when the cystic lesions are small. The presence of a small calvarial defect adjacent to the cystic mass and a persistent primitive falcine vein, which points towards the cystic mass, are imaging clues to this diagnosis. Correct diagnosis is needed prior to surgical resection to avoid potentially serious postoperative complications.

Introduction

Palpable midline soft tissue masses in the parietal/occipital region have a broad differential diagnosis in newborns and infants, which includes dermatologic pathologies such as dermoid/epidermoid cyst, sebaceous cyst, lipoma, or tumors; vascular lesions such as hemangioma or sinus pericranii; or neural tube defects such an atretic cephalocele or encephalocele. Correct diagnosis of the palpable lesion is important for proper medical or surgical management. Ultrasound is often used as an initial imaging modality for work-up of these lesions in infants. It helps determine whether the lesion is cystic or has a soft tissue component and allows evaluation for vascularity within the lesion. Magnetic resonance imaging (MRI) of the brain is however the imaging method of choice for diagnosis of a midline posterior soft tissue mass of the scalp due to the possibility of intracranial extension. Careful evaluation of the imaging is needed to look for calvarial defects adjacent to the lesion, which can lead to the diagnosis of a cephalocele. CT scans are generally avoided in newborns and infants due to the risks of radiation exposure; however, a CT scan can be used in rare cases where the diagnosis is uncertain on MRI imaging.

Cephaloceles are a herniation of intracranial contents through a defect in the calvarium and can contain cerebrospinal fluid (CSF) lined by meninges (meningocele) or CSF, meninges, and brain tissue (encephalocele). Encephaloceles are a form of cranial dysraphism due to failure of closure of the cranial neural tube. ¹

The incidence of encephaloceles is rare and presents in 1 in 3,000 to 1 in 10,000 live births in the United States. ² Approximately 90% of these cases will involve the midline. ² Occipital encephaloceles have a female predominance. ³ As with many other neural tube defects, there are many associations with chromosomal abnormalities, though sporadic encephaloceles do occur and portend a better prognosis. In general, occipital encephaloceles have a poor prognosis and the mortality rate of newborns with these may be as high as 55–83%. ² Factors associated with poorer outcomes include large size of the lesion, significant herniation of brain tissues, presence of other malformations, and the presence of hydrocephalus. ²

Atretic cephalocele is a form of cephalocele which contains meninges, neural rests, and glial rests, which is thought to represent an involuted encephalocele or meningocele. ⁴ Atretic cephaloceles contain only fibrous tissue and dysplastic neuronal tissue, unlike encephaloceles which have a true herniation of brain tissue. These can occur in the occipital or parietal area. ⁵ The frequency of atretic cephaloceles is not well documented and only exists in small scale studies. In patients with an isolated atretic cephalocele and no other fetal anomalies, these are considered benign lesions, and normal neurological development can be expected. ⁶

In this case series, we present multiple cases of atretic encephaloceles encountered at our institution as well as a case of occipital encephalocele for comparison.

Case presentations

Case 1: Atretic cephalocele

This patient was diagnosed with an occipital encephalocele during a prenatal ultrasound. The patient’s mother was referred for a fetal MRI. The MRI was performed at 32 weeks and 3 days gestational age and demonstrated findings of a midline cystic mass along the posterior calvarium of the fetus (Image 1). No herniation of brain tissue was found within the mass on fetal MRI. The presence of a primitive falcine vein pointing towards the opening of the cystic mass is concerning for an atretic cephalocele.

Image 1.

Fetal MRI sagittal T2 HASTE sequence demonstrates a cystic mass protruding from the posterior parietal calvarium in the midline (green arrow). A primitive falcine vein points towards the opening of the cystic mass (blue arrow).

The patient’s mother was referred to both pediatric neurology and neurosurgery in the prenatal period. Admission to the NICU, neurosurgery consult, and repeat MRI/MRV after birth was anticipated.

Patient’s mother presented with preeclampsia with severe features and was delivered via cesarean section at 37 weeks and 6 days. Evaluation of the patient after birth showed skin covering the large cystic mass (Image 2).

Image 2.

Clinical image obtained at birth, which shows the posterior scalp cystic mass. The mass was well covered with a layer of skin.

The MRI after birth demonstrated a small left paramedian posterior parietal skull defect with herniation of CSF into the posterior parietal cystic mass (Images 3(a) and (b)). A persistent primitive falcine vein pointed toward the cystic mass and there was absence of the straight sinus. While herniation of brain tissue was not noted, there was internal complexity to the CSF intensity. MRV of the brain showed a persistent primitive falcine vein, which pointed to the opening of the cystic mass (Image 3(c)). These findings confirmed the presence of an atretic parietal cephalocele.

Image 3.

MRI brain ((a) axial T1 MPRAGE and (b) axial T2) and MRV brain (3c 2D MIP) obtained shortly after birth. The MRI brain ((a) and (b)) confirms the presence of a cystic mass (green arrow), which is protruding through a small, sharply demarcated defect in the posterior parietal calvarium (blue arrow). The mass contains mildly complex fluid, but no signs of herniated brain tissue. The MRV brain (c) shows a persistent primitive falcine vein (yellow arrow) and absence of the straight sinus.

At present, the patient demonstrates normal neurologic development. There is a tentative plan for neurosurgical repair at 6–9 months of age.

Case 2: Atretic cephalocele

Patient was born at 38 weeks due to maternal hypertension. As an infant, the patient was evaluated by pediatric surgery for a small soft tissue mass at the vertex of the scalp, which was nontender and had been present since birth. The child had no past medical history and presented with normal neurologic development. Ultrasound of the mass was ordered to look for intracranial extension given the midline posterior location. The ultrasound raised concern for intracranial extension and the patient was referred for an MRI of the brain. Ultrafast Brain MRI (multiplanar T2 HASTE sequences) was obtained and revealed a small cystic lesion in the scalp (Image 4(a)). No defect in the calvarium was identified on the MRI.

Image 4.

MRI brain ((a) axial T2 HASTE and (b) sagittal T2 HASTE) without intravenous contrast demonstrates the small cystic scalp mass (blue/green arrow). While no definitive calvarial defect was identified on MRI, there is a suggestion of a primitive falcine vein (yellow arrow), which points to the cystic mass. Findings are suspicious for an atretic cephalocele.

Resection of the lesion was complicated by sagittal sinus thrombosis, venous infarcts, and subdural hematoma. Retrospectively, the presence of a persistent primitive falcine vein pointing toward the location of the cyst (Image 4(b)) could have raised suspicion of an atretic parietal cephalocele even though a definite defect in the calvarium was not identified on the limited HASTE T2 images.

Case 3: Atretic cephalocele

This patient was born at 35 weeks due to premature rupture of membranes. Patient had multiple fetal anomalies diagnosed prenatally and was eventually diagnosed with VACTRL association (truncus arteriosus type I, TEF with esophageal atresia, and imperforate anus).

On routine head ultrasound, the patient was found to have bilateral grade 1 germinal matrix hemorrhages, enlarged ventricles, and enlarged extra-axial CSF space. Brain MRI was then obtained for further evaluation. The Brain MRI showed a persistent falcine vein (Image 5(a)) which pointed to a tiny subcentimeter cystic scalp lesion (Image 5(b)). Findings were highly suspicious for atretic cephalocele.

Image 5.

MRI brain obtained with and without contrast. Image 5(a) (coronal T2 HASTE) shows a small midline cystic scalp mass (green arrow). Image 5(b) (sagittal T1 MPRAGE post contrast) shows a persistent primitive falcine vein (blue arrow), which points towards the cystic mass. A small defect is suspected in the posterior parietal calvarium, though not definitely visualized.

A CTV head was performed at a later date on this patient and nicely demonstrates the small calvarial defect adjacent to the small cystic scalp lesion. The CTV also confirmed the persistence of a primitive falcine vein (Images 6(a) and (b)).

Image 6.

CTV head ((a) axial and (b) sagittal) confirmed the findings of a small posterior parietal calvarial defect adjacent to the small cystic mass (green/blue arrow). An enlarged primitive falcine vein is noted (yellow arrow), which points toward the cystic mass.

Neurosurgery has deferred any surgical management of this lesion at this time given the patient’s complex medical issues and ongoing surgeries for congenital heart disease.

Companion case: Occipital encephalocele

This patient was diagnosed with occipital encephalocele via prenatal ultrasound. The patient’s mother was referred for a fetal MRI. Fetal MRI was obtained at 32 weeks gestational age. The fetal MRI showed a defect in the posterior occipital calvarium with a small amount of cerebellum protruding through the defect. The herniated brain tissue was covered by a thin layer of CSF and meninges, consistent with an encephalocele, which was then surrounded by a larger pseudomeningocele (Image 7). Additionally, colpocephaly and concern for polymicrogyria of the occipital lobes was noted.

Image 7.

Fetal MRI (sagittal T2 HASTE) showed a posterior cystic mass protruding through a defect in the occipital calvarium (green arrow) with herniation of the cerebellum. The herniated cerebellum is covered by a thin layer of CSF and meninges consistent with an encephalocele (yellow arrow). The encephalocele is surrounded by a larger pseudomeningocele.

Patient was delivered at 36 weeks and 2 days gestational age due to premature rupture of membranes. A thin layer of skin surrounds the large posterior encephalocele at birth, which appeared ulcerated (Image 8).

Image 8.

Clinical image of the large posterior midline cystic mass measuring up to 31 cm.

MRI and MRV of the brain were obtained immediately after birth. The MRI revealed a large occipital encephalocele with herniation of the distorted occipital lobes. Additionally, there was cerebellar hypoplasia, the fourth ventricle was effaced, and there was tectal beaking (Image 9(a)). MRV showed patency of the internal cerebral veins, vein of Galen, and straight sinus, which drained into the right transverse sinus. Left transverse sinus appeared patent as well. The distal aspect of the superior sagittal sinus and the confluence of sinuses was not visualized, which was concerning for herniation of the torcula (Image 9(b)).

Image 9.

Image 9(a) (MRI brain sagittal T2 HASTE) demonstrates a large posterior occipital encephalocele with herniation of the distorted occipital lobes (green arrow). Image 9(b) (MRV brain 2D MIP) shows patent superficial and deep cerebral veins with presence of a straight sinus and absence of herniation of the venous structures into the sac.

Patient underwent surgical repair of the encephalocele with no known postoperative complications. Despite no surgical complications, the patient has demonstrated development delays in motor skills as well as hearing and visual impairments, likely due to abnormalities in the posterior portions of the brain.

Discussion

Making the correct diagnosis of atretic cephalocele is important for optimal surgical management and avoidance of postoperative complications. Atretic cephaloceles can be small or large as seen in the cases presented in this article. Small atretic cephaloceles may go undiagnosed into childhood or even adulthood. In the absence of other fetal anomalies, an atretic cephalocele has a favorable prognosis and normal neurologic development can be expected.

For newborns and infants with a midline scalp lesion in the posterior parietal or occipital region, imaging is imperative to look for intracranial extension of a cystic or soft tissue mass. Initial evaluation can be performed with a neonatal head ultrasound; however, in most cases, an MRI brain is needed to exclude a calvarial defect and intracranial communication. If a calvarial defect is seen, a small differential diagnosis exists, which includes occipital/parietal encephalocele, atretic cephalocele, or sinus pericranii. To distinguish these entities and to look for associated abnormalities, an MRV should be obtained at the time of the MRI brain to look at the dural venous anatomy.

An occipital encephalocele can be distinguished from the other two entities by the presence of brain tissue herniating through the calvarial defect. An MRV is imperative to evaluate for herniation of the torcula or other venous structures.

Sinus pericranii is an abnormal connection between the superior sagittal sinus and extracranial venous structures via an emissary vein. The emissary vein traverses intraosseously and can cause a notable gap in the calvarium especially if enlarged. MRV (or CTV) is helpful to identify the emissary vein which will distinguish sinus pericranii from a cephalocele.

An atretic cephalocele does not contain any brain tissue, though glial and neural rests can be present, giving the cystic lesion some complexity. Atretic cephaloceles are closely associated with a persistent primitive falcine vein, which is sometimes incorrectly referred to as vertical straightening and elevation of the straight sinus. The falcine vein, which connects the vein of Galen/straight sinus with the superior sagittal sinus, is present in the prenatal period, but is rarely present after birth. An MRV should always be obtained in evaluation of posterior midline masses because the presence of a primitive falcine vein, which points to the cystic lesion, is highly suspicious for an atretic cephalocele.

Small atretic cephaloceles can be misdiagnosed if you are not looking for a calvarial defect or the presence of a falcine vein. Failure to recognize an atretic cephalocele prior to resection of that lesion can lead to operative complications. The major operative complication of these lesions is accidental tear of the sagittal sinus, which can cause hemorrhage and lead to hemodynamic instability. ⁷ In properly diagnosed patients, surgical repair includes repair of both the dural and calvarial defects.

ORCID iDs

Hallie Whalen https://orcid.org/0000-0002-3299-5052

Sandrine Yazbek https://orcid.org/0000-0002-5557-7371