Leptomeningeal Cyst

Etiology

Fall-related incidents are the most common causes of LMC.[5] The parietal bone is the site of occurrence.[3] Case reports have described the leptomeningeal cyst occurrence from reconstructive craniofacial surgeries and craniosynostosis reconstruction, including simple suturectomy and extensive calvarial vault remodeling.[6][7] Endoscopic repair has also been reported as a cause of leptomeningeal cysts.[8] In rare instances, vacuum extraction, a form of assisted delivery, is reported to cause leptomeningeal cysts in newborns.[9][10]

Epidemiology

The incidence of LMC is approximately 0.05% to 1.6%. More than 90% of these cases occur below three years of age.[3][11] This may be related to the following:

• The rapid growth of the brain and skull.
• Dense adherence of the underlying dura to the bone.
• Skulls are thinner and more deformable.[2]

One of the studies described the mean age at the trauma as 8.8 months and the mean age at presentation as 21.9 months, with a slight predominance in male infants.[12] Presentation in adults is rare and almost invariably has a preceding history of head trauma.[13][14]

Pathophysiology

Concurrent underlying dural tear with herniation of the brain elements egressing through the fracture site is the primary variable governing the development of LMC.[15]

 Four essential prerequisites for the development of LMC include:

• Skull fractures are sustained mostly below three years of age.
• There is an underlying dural tear.
• This leads to the interposition and continuum herniation of brain elements through the defect based on the ‘ball-valve’ mechanism, and
• There occurs progressive advancement of the fracture line.[2][3][5]

Phases described in the development of LMC include:

• The first phase- includes skull fracture with an underlying dural tear.
• The second phase- includes healing of the fracture margins hindered by invagination and entrapment of arachnoids and governed by brain pulsation.
• The last phase- is characterized by bone diastasis alongside the leptomeningeal herniation.[16]

The progression of growing LMC has been described into three stages:

• Stage 1- is from the time of ictus but before the onset of fracture enlargement.
• Stage 2- is the first two months of the beginning of fracture enlargement.
• Stage 3- is after two months of fracture enlargement.[2][17]

Histopathology

Histopathological tissue at surgery appears to be variable depending on the swelling content. The outer skull table appears thinned, and the mass is usually soft and connected to the underlying brain through a dura defect. The tissue was congruent with the gliotic brain.[4]

History and Physical

The scalp swelling is usually first brought to the attention of caregivers. Depending on the contents, the mass is either soft or hard. Progressive but painless scalp swelling is the most common pattern of clinical presentation.[18] The symptomatology varies regarding severity, chronicity, and injury site.[17] These include:

• Pulsatile scalp mass aggravated by cough and crying impulses.
• Headache.
• Loss of consciousness.
• Seizures.
• Neurological deficits.
• Impaired vision, squint, and proptosis.
• Mental retardation.
• Gross skull deformity.[3][19]

Neurological deficit (40%) and loss of consciousness (86%) are frequent among children who present late.[19] Delayed seizures and new onset/progression of deficits harbinger the disease evolution.[18] In adults, the initial presentation could be swelling associated with headaches and scalp paraesthesia-dysesthesia.

In a study of 440 patients, the mean presentation age was 21.9 months. 57.8% of them were males.[12] Another study comprising 67 patients showed 86.67% of patients sustained the injury prior to three years of age. Seizures were observed in 41.80% of cases.[19] There is a variable time lapse between the index injury and the clinical presentation of  LMC, varying from <6 months to more than 20 years.[18][19]

Evaluation

Diagnosis can be established with an antecedent history of trauma and neuroimaging modalities such as plain radiographs, computed tomography (CT), and magnetic resonance imaging (MRI). Imaging is imperative to define the extent of primary skull fracture and associated encephalomalacia, aid in surgical planning, and exclude other pathologies.

• Plain X-ray skull- early phase shows the diastatic fracture. Late lesions may show lytic lesions with scalloped margins.
• CT brain- In addition to the findings in the plain radiograph, the early phase shows concurrent lesions, with brain contusions being the most common finding.[19] In the late stage, CT imaging shows the presence of a leptomeningeal cyst, intradiploic cyst, encephalomalacia, porencephalic cyst, ventricular asymmetry, and hydrocephalus.[3][19] 3D CT is better at detecting fracture patterns.[20]
• MRI-The main advantage of MRI is early detection of the defect in the dura and concurrent herniated brain elements in high risks patients.[3]Patients with:
  • Cephalhematoma
  • Bone diastasis of 4 mm or more, and
  • Underlying brain contusion should ideally have a contrast brain MRI to find out the dural tear and herniation of the brain matter.[15]
• Color Doppler imaging-useful for newborns who develop leptomeningeal cysts due to birth trauma.[21] Doppler imaging also reveals pulsatile arterial flow thought to be from the arterial flow in the dural space, thereby excluding avascular masses such as cephalhematoma or subgaleal bleeding. Doppler could also aid in evaluating for any concomitant venous injury.
• Seizures warrant evaluation with an electroencephalogram.

Three primary types of LMCs:

• Type 1- contains a leptomeningeal cyst in the calvarial defect.
• Type 2-contains encephalomalacia and gliotic brain tissue in the defect, or
• Type 3- contains a porencephalic cyst in the subgaleal space in the subperiosteal layer.[5][17][22]

Treatment / Management

Early diagnosis and surgical intervention are crucial to avoid progressive and potentially permanent neurological sequelae. The surgical intervention of the leptomeningeal cyst involves a craniotomy, resection of the mass, repair of the dural defect with a pericranial patch, and repair with a bone graft. In one case report, fibrinogen-based collagen fleece was used as an alternative to dural repair. [23] The fibrinogen and thrombin imitate the last steps of the coagulation cascade. The coagulation factors dissolve upon contact with bleeding wounds or bodily fluids, and a link is formed between the collagen carrier and the wound surface.[23](B3)

Although primary closure of the dural defect is the definitive treatment, recurrence of the cyst (2%) remains possible.[12] Syndromic craniosynostosis, hydrocephalus, elevated intracranial pressure, repeated surgical interventions, endoscopic repair,  and incomplete duraplasty/cranioplasty are all risk factors associated with the recurrence of leptomeningeal cysts. During initial craniosynostosis repair, mannitol can be administered to relax the brain and prevent injury to the dura. 

The management of elevated intracranial pressure is crucial to prevent cyst recurrence. Surgically, increased intracranial pressure can be treated by resecting herniated brain matter and treating hydrocephalus. Repair should be delayed until herniated brain tissue is apparent on brain imaging. It is suggested that the repair be postponed until the edema subsides and the brain tissue retracts from the defect. However, if the herniated tissue continues despite sufficient surveillance, which is usually up to two months, excision of the nonfunctional tissue is required. After this period, it is unlikely that the cyst will regress spontaneously and generally continue to grow without surgical intervention.[12]

Ventriculoperitoneal (VP) shunting is another method that can be utilized to treat hydrocephalus or increased intracranial pressure.[6] In individuals with hydrocephalus, VP shunting and the resulting cerebrospinal fluid diversion may occasionally be used alone to treat recurrent leptomeningeal cysts.[24] Cranioplasty should preferably be performed with a bone graft secured with rigid absorbable screws and plates or absorbable sutures, although a split-thickness graft is also appropriate.[7](B3)

Pivotal Aspects in the Management

The salient surgical steps in the management include:

• Defining the edges of the bony defect.
• Wide craniotomy to expose the dural defect.
• Excision of the meningo-cerebral cicatrix.
• Watertight duroplasty.
• Repair of the bony defect.[19]

Watertight closure of the dural defect and cranioplasty is the mainstay of management. The dural defects are, on average, 1.42 times larger than the bony defects.[19] Wide exposure of the dural margins by liberal craniectomy is, therefore, of paramount importance.[16] The removal of the leptomeningeal cyst, followed by safe resection of the encephalomalacia, is undertaken.[3] Watertight closure of the dural defect through the use of autologous grafts such as pericranium and fascia lata have improved outcomes owing to better tissue compatibility and minimized risk of infections, adhesions, and rejections.[11] A split calvarial bone graft is advocated for children below three years old.[25] This, however, has increased the risk of resorption owing to brain pulsation.[11] Titanium mesh which has excellent biocompatibility, a low infection rate, and high mechanical strength, is preferred for cranioplasty.[5] Endoscopic-assisted duraplasty with the use of collagen matrix has also been described.[11](B3)

Orbital roof repair is required for orbitofrontal variants of LMC.[26] Lesions involving or in the vicinity of the major dural venous sinuses should ideally not be surgically intervened.[5](B3)

Differential Diagnosis

• Intradiploic encephalocele.
• Intradiploic arachnoid cyst.
• Post traumatic lipomas.
• Meningeal melanocytoma.
• Congenital parietal bone agenesis.
• Menkes disease.
• Eosinophilic granulomas.
• Langerhans cell histiocytosis.
• Multiple myelomas.
• Epidermoid cyst.
• Osteomyelitis.
• Calvarial metastasis.[19][27][28]

An intracranial epidermoid cyst is a rare congenital cyst that appears as lobulated lesions that fill and enlarge cerebrospinal fluid spaces and have the same density as cerebrospinal fluid on CT. On skull CT, Langerhans cell histiocytosis presents as solitary or multiple punched-out lytic lesions devoid of a sclerotic rim; "beveled edges" or "button sequestrum" may be observed due to the involvement of inner and outer tables.[29] Multiple myeloma of the calvarium manifests as well-defined lytic lesions without sclerotic rims (punched-out lesions) of varying sizes distributed throughout the skull.[29]

Osteomyelitis is characterized by focal bone lysis, cortical loss, periosteal thickening, and endosteal scalloping on plain radiographs. Depending on the underlying malignancy, calvarial metastasis manifests as either a lytic or sclerotic lesion; occasionally, mixed lytic and sclerotic lesions are observed. Metastatic lesions of the skull are frequently multiple; however, a single metastatic lesion may also be present.[29] The radiological appearance of congenital calvarial defects could vary depending on the condition, such as the partial or complete absence of cranial vault bones, abnormal cerebral hemisphere development, incomplete medical parietal bone suture, delayed or incomplete ossification of the membranous parietal bone. Other possible diagnoses include an intradiploic arachnoid cyst. These are likely congenital and result from a restriction in the flow of cerebrospinal fluid from the arachnoid granulations into the veins. These cysts typically manifest as localized pain, swelling, seizures, or neurological deficits late in life.[14]

Cephaloceles are congenital herniations of intracranial structures resulting from a skull defect.[30][31] Cephaloceles are classified based on the location and content of the herniated tissue. Meningocele is a protrusion of the meninges and cerebrospinal fluid only, whereas encephalocele involves a protrusion of the meninges, cerebrospinal fluid, and brain tissue. The encephalocystocele comprises meninges, cerebrospinal fluid, brain tissue, and ventricle. The term atretic cephalocele refers to a lesion in the midline that contains meninges, fibrous tissue, and dysplastic brain tissue.[32]

Prognosis

The leptomeningeal cyst is benign and carries a good prognosis. However, timely diagnosis and prompt surgical repair are crucial to avoiding long-term complications. The cyst can remain asymptomatic in some individuals; however, it still requires repair, given the risk of progressive enlargement and irreversible neurological complications. In addition, epilepsy, brain herniation with neurological deficit, and mental retardation can be associated with poor quality of life and significant morbidity.

Good-to-excellent outcomes, even in the delayed presentation, are observed in most cases.[18] In a study of 440 patients, dura-cranioplasty was performed in 61.6%.[12] Improvement in seizures and neurological deficits was noted in 12.7% and 7.05% of cases.[12]

Poor prognostic factors in one study included:

• Significant bony defect (>7 cm).
• Initial severe head injury.
• Calvarial defects crossing the midline, and
• Delayed repair (>8 months).[18]

Comminuted fracture (OR, 7.572) and the degree of diastasis (OR, 2.081 per mm diastasis) have a significant role in developing growing skull fractures.[33] Children at risk for developing GSF should be monitored clinically for up to 3 months following the initial insult.[12] A high index of suspicion is required among children with cephalohematoma persisting even after two weeks of trauma.[34]

Complications

Complications

• Rupture and subgaleal CSF collection.
• Ipsilateral ventricular dilatation.
• Hydrocephalus.
• Seizures.
• Progressive neurological deficits.
• Mental retardation.[2][35]

Complications of Surgery

• Wound infection.
• Subdural hygroma.
• CSF leaks and meningitis.
• Lesions communicating to the ventricles can lead to potentially life-threatening hemorrhagic complications due to sagging of the brain and rupture of draining veins.
• Recurrence.
• Mortality due to anesthesia and meningitis (reported in up to 8% of cases).[19][36]