Posttraumatic leptomeningeal cysts (PTLMC) (sometimes just traumatic leptomeningeal cysts), AKA growing skull fractures consists of a fracture line that widens with time.
The term cyst is actually a misnomer, as it is not a cyst, but an extension of the encephalomalacia 1).
Posttraumatic leptomeningeal cysts were first described in 1816, 2).
Very rare, occurring in 0.05–0.6% of skull fractures 3) 4). Usually requires both a widely separated fracture AND a dural tear.
Mean age at injury: < 1 year; over 90% occur before age 3 years 5) (formation may require the presence of a rapidly growing brain 6)), although rare adult cases have been described 7), 8) 9) (a total of 5 cases in the literature as of 1998 10)).
The pathophysiology and some aspects of its management are still controversial.
It is thought they occur secondary to skull fractures causing dural tears allowing the leptomeninges and/or cerebral parenchyma to herniate into it
Pulsations from CSF erode the fracture margin, resulting in eventual expansion and non-union.
It occurs due to a wide skull defect with underlying dural defect and changes in pressure gradients within the skull cavity. Neglected cases may develop progressive neurological deficits and complications after second head trauma 11).
Enlarging scalp mass
Focal neurological deficit
Most often presents as scalp mass (usually subgaleal), although there are reports of presentation with head pain alone 12).
Kitumba and Mascarenhas presented a rare case of an adult with excruciating headache secondary to a post-traumatic fronto-orbital leptomeningeal cyst 13)
PTLMCs rarely occur > 6 mos out from the injury. Some children may develop a skull fracture that seems to grow during the initial few weeks that is not accompanied by a subgaleal mass, and that heals spontaneously within several months; the term “pseudogrowing fracture” has been suggested for these 14).
They can rupture and cause diffuse subgaleal CSF collection 15).
Radiographic findings: progressive widening of fracture and scalloping (or saucering) of edges.
round or oval lucency with smooth margins
CT scan is the modality of choice for the evaluation of leptomeningeal cyst. It consists of a lytic calvarial lesion with scalloped edges, in which encephalomalacia invaginates. The following features may also be present
extracranial brain herniation
unilateral ventricular dilatation
Guler I, Buyukterzi M, Oner O, Tolu I. Post-traumatic leptomeningeal cyst in a child: computed tomography and magnetic resonance imaging findings. J Emerg Med. 2015 May;48(5):e121-2. doi: 10.1016/j.jemermed.2014.12.042. Epub 2015 Feb 3. PMID: 25662419.
Not to be confused with arachnoid cysts (AKA leptomeningeal cysts, which are not posttraumatic).
Posttraumatic intradiploic leptomeningeal cyst.
Skull tumor 16).
congenital calvarial defect
Although usually asymptomatic, the cyst may cause a mass effect with neurologic deficit.
Distal cortical artery aneurysms: often associated with an overlying s skull fracture, sometimes a growing skull fracture
Neglected GSF can rupture and cause diffuse subgaleal CSF collection 17).
If early growth of a fracture line with no subgaleal mass is noted, repeat skull films in 1–2 months before operating (to rule out pseudogrowing fracture). In young patients with separated skull fractures (the width of the initial fracture is rarely mentioned), consider obtaining follow-up skull film 6–12 mos post-trauma. However, since most PTLMCs are brought to medical attention when the palpable mass is noticed, routine follow-up X-rays may not be cost-effective.
Treatment of true PTLMC is surgical, with dural closure mandatory. Since the dural defect is usually larger than the bony defect, it may be advantageous to perform a craniotomy around the fracture site, repair the dural defect, and replace the bone 18).
The dural substitutes used are either autografts (which may not be enough) or artificial grafts (which are foreign-body implantations and which also may be too expensive in a low-resource practice).
Adeleye presented the surgical description of the use of the cyst capsule as a cost-free autologous graft in the surgical repair of the dural defects of two cases of traumatic leptomeningeal cyst 19).
Pseudogrowing fractures should be followed with X- rays and operated only if expansion persists beyond several months or if a subgaleal mass is present.
Liu et al. performed a retrospective review of 27 patients with GSF, who were grouped according to 3 different GSF stages.
Over a period of 20 years, 27 patients with GSF (16 males and 11 females) were treated in the authors’ department. The mean follow-up period was 26.5 months. Six patients were in the pre-phase of GSF (Stage 1), 10 patients in the early phase (Stage 2), and 11 in the late phase (Stage 3). All patients underwent duraplasty. All 6 patients at Stage 1 and 5 patients at Stage 2 underwent craniotomy without cranioplasty. Five patients at Stage 2 and all of the patients at Stage 3 underwent cranioplasty with autologous bone and alloplastic materials, respectively. Among all patients, 5 underwent ventriculoperitoneal shunt placement. Symptoms in all patients at Stages 1 and 2 were alleviated or disappeared, and the cranial bones developed without deformity during follow-up. Among patients with Stage 3 GSF, no obvious improvement in neurological deficits was observed. Three patients underwent additional operations because of cranial deformation or infection.
The authors identify the stages of GSF according to a new hypothesis. They conclude that accurately diagnosing and treating GSF during Stages 1 and 2 leads to a better prognosis 20)
Kulkarni et al. presented a 14-year-old child who developed sudden-onset, diffuse, soft, fluctuant, circumferential swelling of the head after a road traffic accident. He had sustained a head injury at the age of 3-months leading to an asymptomatic soft swelling over the skull which was left untreated. The present CT scan of the brain showed a bony defect with ragged edges and cerebrospinal fluid (CSF) collection in subgaleal space circumferentially. He underwent exploration, duroplasty, and cranioplasty and had a good outcome.
Neglected GSF can rupture and cause diffuse subgaleal CSF collection. It should be managed with dural repair and cranioplasty 21).
Kitumba D, Mascarenhas L. Rare case of an adult with excruciating headache secondary to post-traumatic fronto-orbital leptomeningeal cyst. Neurochirurgie. 2020 Nov;66(5):410-411. doi: 10.1016/j.neuchi.2020.06.126. Epub 2020 Aug 7. PMID: 32777233 22).
A 4-year-old boy was brought to the emergency department after suffering from head trauma caused by a fall from a rooftop where he was treated conservatively at a local hospital. Later, he developed swelling in the occipital region and was brought to the department of neurosurgery where he was operated on. After the first surgery, recurrence of swelling was seen after a postoperative period of 2 months, and a computed tomography scan reported persistent epidural hygroma with extension into the subcutaneous space. The second surgery was performed, and a 12-month follow-up did not show any recurrence of swelling in the patient 23).
A full-term infant born after a nontraumatic, forceps-assisted spontaneous delivery, who developed an increasing cystic swelling over the left frontoparietal area that crossed over coronal and sagittal sutures. The lesion was initially misinterpreted as cephalhematoma. Clinical and radiological follow-up established the correct diagnosis of leptomeningeal cyst.
The collection was initially tapped. Surgical treatment was undertaken thereafter, consisting of decompression and resection of the cyst and dural repair. Two months after follow-up, the patient remains asymptomatic and the porencephalic cavity remains isolated from the extradural space, with no evidence of new fluid collections 24).
A 53-year-old female presented with a post-traumatic leptomeningeal cyst manifesting as bulging of the scalp, dizziness, and tinnitus. She had known of the bulging of her forehead for about 20 years. She had suffered an injury to the head in childhood. Brain CT revealed a bone cyst associated with a round bone defect in the left frontal bone, bulging of the very thin outer layer, and the defective inner layer. She was treated surgically with a diagnosis of a skull tumor, but only gray cystic membranous tissue was found. The dural defect was repaired with fascia and the bone defect with bone cement. Bulging of the skull in adults can be caused by a bone cyst originating from a skull fracture 25).
12 patients diagnosed and treated between 1980 and 2002. 11 patients were under the age of 3 years and one patient was 5 years old at the moment of HI. The most common cause of injury was a fall from height. In the initial plain x-rayfilms, 11 patients showed a diastatic skull fracture and one patient only had a linear fracture. At this time, CT scan showed cortical contussion underlying the fracture in every case. The mean time between injury and presentation of GSF was 11.6 weeks. Diagnosis was made by palpation of the cranial defect and confirmed with skull x-rayfilms. The most frecuent location of GSF was in the parietal region. Associated lesions like hydrocephalus, encephalomalacia, leptomenigeal cysts, brain tissue herniation and ipsilateral ventricular dilatation, were found in the preoperative CT or MRI. All patients underwent a dural repair with pericranium or fascia lata. The cranial defect was covered with local calvarial bone fragments in every case. Only one patient needed a cranioplasty with titanium mesh. Every child with a skull fracture must be followed until the fracture heals. Patients under the age of 3 years with a diastatic fracture and a dural tear, demostrated by TC or MRI, are more prone to develop GSF. In these cases, early repair must be adviced in order to prevent progressive brain damage 26).
A growing skull fracture associated with cerebrospinal fluid rhinorrhoea following trauma sustained in adult life. The natural history of its development, diagnosis, and the results of surgery are discussed. The literature is reviewed with regard to aetiology, incidence, imaging characteristics and management of this rare post-traumatic complication 27).
A lump in the right parietal region of this 53-year-old man prompted a computed tomography (CT) scan. The patient denied any symptoms and was in good health. The examination confirmed a firm, non-tender, non-pulsatile mass in the right parietal region of the skull. The CT scan demonstrated a 4 x 3 cm area of irregular bone destruction involving both the inner and outer table of the skull. At operation a distinctly raised paper-thin outer table was noted, and underneath was a soft, tan-colored mass, which measured approximately 2 x 2 cm and was connected to the underlying brain through a 1 cm dural defect. The extradural portion of the mass was amputated, the dura repaired with a pericranium patch, the skull defect was repaired with a split-thickness bone graft, and the final pathology was congruent with a gliotic brain 28).
Meloche BR, Sansregret A, Grégoire H, Gagnon J, Massicotte P. Un cas de kyste leptoméningé post-traumatique [A case of post-traumatic leptomeningeal cyst]. Union Med Can. 1967 Oct;96(10):1214-9. French. PMID: 5601803.
PEYSER E, WEISSBERG D. Post-traumatic arachnoidal cyst. Report of an unusual case. J Neurosurg. 1961 Jul;18:551-3. doi: 10.3171/jns.1961.18.4.0551. PMID: 13735101.