Out of the box: Pancraniosynostosis with leptomeningeal cyst

A 3-year-old female presented with a seizure to the emergency department. She also had a soft, compressible swelling on the left side of the head, continuously increasing in size in the last 6 months. The patient had a history of trauma 1 year back for which no treatment was sought by the parent, considering the trauma was trivial. On examination, the patient had dysmorphic facies in the form of a tower skull, flat nasal bridge, hypertelorism and protruding eyeballs (Figure 1). Bilateral papilledema was seen on retinoscopy. Ears appeared low set. Teeth were normal. Hands and feet were normal. No previous workup was done for the patient.

A non-contrast CT head was performed for the patient, which showed increased craniocaudal length of the skull and decreased anteroposterior length suggestive of tower skull. Diffuse crowding of the brain parenchyma and posterior fossa structures with slit-like ventricles. A small defect was seen in the left parietal bone with herniation of brain parenchyma. The herniated tissue showed communication with ipsilateral lateral ventricle diffuse cystic encephalomalacia with multiple calcifications in the walls, causing indentation and scalloping of the outer table of the skull. Diffusely scalloping is seen in the inner table of the skull. Bilateral orbits are small in size with bilateral exophthalmos (Figure 2). Volume-rendered images showed complete fusion of all the cranial sutures with flattening of the frontonasal angle. There was slightly mandibular prognathism. Upper and lower alveolus showed a normal arrangement of teeth (Figure 3).

Background

Progressive postnatal pansynostosis (PPS) is a rare condition with a delayed fusion of the sutures of the skull presenting at a later age, unlike other causes of synostosis diagnosed in prenatal period. It is associated with various syndromes and metabolic disorders like rickets and hypophosphatasia [1,2]. Leptomeningeal cysts or growing skull fractures are chronic complications of trauma in children, occurring in 1% of skull fractures, and represent encephalomalacic brain tissue herniating via the site of fracture, preventing its fusion [3].

Clinical Perspective

Most cases present with raised intracranial pressure or proptosis due to small orbits. Few cases might be incidentally detected with normal intracranial pressure. The head is microcephalic due to fused sutures. Various syndromes associated with craniosynostosis include Crouzon, Pfeiffer, Apert, Saethre-Chotzen, and Muenke syndromes [4]. These syndromes have similar craniofacial features, including craniosynostosis, exophthalmos, midface hypoplasia, cranial base anomalies, and abnormal facies; however, the absence of limb anomalies favours Crouzon syndrome. Metabolic bone diseases like rickets and hypophosphatasia have multiple theories explaining synostosis, but in addition, biochemical and skeletal findings should corroborate. Craniofacial abnormalities are absent in metabolic disorders [2].

Leptomeningeal cysts are seen in children up to 3 years of age. Patients present with enlarging scalp mass associated with seizures, headache or focal neurological deficit depending on the side and site of encephalomalacic brain tissue [3]. The pathogenesis includes dural tear occurring secondary to trauma, causing herniation of brain tissue into the diastatic fracture. Few articles quote CSF pulse pressure and pulsation of the brain in the vicinity of bone defect contributing to the development of leptomeningeal cysts [5]. Our patient gave a history of trauma with scalp swelling, and hence urgent non-contrast computed tomography (NCCT) head was performed.

Imaging Perspective

CT is the imaging modality of choice in patients with craniosynostosis. It can depict signs of increased intracranial pressure in the form of crowding of brain parenchyma, effacement of ventricles, cisternal spaces, and bone changes in the form of endocortical scalloping termed as “copper beaten skull”. Mid-facial hypoplasia and teeth anomalies can also be assessed on CT. Volume rendered technique (VRT) images can depict 3D images of the skull and allow assessment of the sutures. In PPP, all the sutures are fused. An enlarged emissary vein foramina signifies venous hypertension [6].

CT can also demonstrate leptomeningeal cyst as a defect at the fracture site that often appears like a lytic calvarial lesion with scalloped edges through which encephalomalacic brain tissue herniates. There may be associated ipsilateral dilated lateral ventricle, porencephalic cysts and/or hydrocephalus [3,7]. MRI is helpful in early cases where dural tears might be detected, and the status of the herniated brain tissue can be assessed better [8].

Outcome

Surgical management is done to relieve intracranial hypertension, including frontal craniotomy and mid-face advancement in a staged manner. In asymptomatic cases, conservative management is done. For leptomeningeal cysts, surgical excision of the cystic encephalomalacic tissue is recommended in symptomatic cases followed by duraplasty and cranioplasty to prevent its recurrence. In patients with synostosis, there are increased chances of formation of leptomeningeal cysts as there is associated intracranial hypertension. It is impossible to conclude if herniation of brain tissue occurred via an unfused suture during the time of trauma or secondary to fracture in fused sutures. Scalloping of the outer cortex of the skull and calcification in the cyst wall signifies a chronic nature of the pathology.

In our patient, surgical excision of the leptomeningeal cyst was done as a first-stage operation and surgery for craniosynostosis was postponed. Currently, the child is symptom-free.

Take Home Message / Teaching Points

Progressive postnatal craniosynostosis is rare, its syndromic and non-syndromic associations are important to know. Diagnosis of leptomeningeal cysts should be considered in children with scalp swelling with trivial trauma. NCCT with VRT images is an excellent modality to see the sutural anatomy and must be performed in patients with trauma with suspected calvarial pathology.

Written informed patient consent for publication has been obtained.