Differentiation between pediatric spinal arachnoid and epidermoid-dermoid cysts: is diffusion-weighted MRI useful?

Transcerebellar ventriculoperitoneal shunt for management of presumed arachnoid diverticulum in the fourth ventricle of a dog

OBJECTIVE

To describe the approach for placement of a transcerebellar fourth ventriculoperitoneal shunt for management of presumed fourth ventricle arachnoid diverticulum and secondary obstructive hydrocephalus of a dog. To describe the outcome of this procedure.

STUDY DESIGN

Case report.

ANIMALS

Male entire English springer spaniel, 3 years 9 months of age.

METHODS

The dog was initially presented for management of acute, progressive, and multifocal brainstem and forebrain dysfunction. Magnetic resonance imaging revealed internal obstructive hypertensive hydrocephalus. The dog was managed via ventriculoperitoneal shunting from the left lateral ventricle and made an excellent recovery. The dog acutely deteriorated 18 months after initial discharge and follow-up magnetic resonance imaging confirmed the ventricular shunt remained in situ with normal-sized lateral ventricles but revealed a cystlike lesion within the fourth ventricle, presumed to be a fourth ventricle arachnoid diverticulum. The diverticulum was causing mass effect and resultant compression of adjacent neuroparenchyma. A second ventriculoperitoneal shunt was subsequently placed into the fourth ventricle via the caudal cranial fossa and cerebellum. This was attached to a three-way connector, to which the existing shunt (within the left lateral ventricle) was also attached, and then secured to the existing medium-pressure valve.

RESULTS

Postoperatively, the dog immediately developed mild vestibular-cerebellar ataxia, with a marked improvement after 3 months. There were no shunt-associated complications. Long-term follow up at 40 months after the second surgical procedure revealed a normal neurological examination.

CONCLUSION

Transcerebellar ventriculoperitoneal shunt placement for treatment of a presumed fourth ventricle arachnoid diverticulum was performed and was associated with a favorable long-term outcome.

Congenital Spinal Cysts: An Update and Review of the Literature

Congenital spinal cysts are rare and encompass a wide variety of diseases including arachnoid, enterogenous, teratomatous, neurenteric, foregut, bronchogenic, epithelial, ependymal, dermoid, and epidermoid cysts. Here, we elucidate the epidemiology, pathology, pathogenesis, and diagnostic findings of the most common congenital spinal cysts, followed by a discussion of their presentation and treatment options. Differentiating the cause of each lesion is crucial for targeted clinical and surgical management for the patient. Our review describes how arachnoid cysts can be observed, fenestrated, percutaneously drained, or shunted; however, the primary goal for neurenteric, dermoid, and epidermoid cysts is removal. Further, we discuss how patient presentation is dependent on the rate of growth and location of compression on the spinal cord and nerve roots. However, although many of these lesions are discovered incidentally on imaging, the spectrum of possible symptoms include pain, weakness, ataxia, bladder incontinence, and progressive or acute neurologic deficits. We present and review the histology and imaging of a variety of cysts and discuss how although the goal of treatment is resection, the risks of surgery must be considered against the benefits of complete resection in each case.

A Rare Case of Infected Cervicodorsal Intramedullary Epidermoid Cyst

Introduction  Intramedullary spinal epidermoid cysts have a reported incidence of less than 1% of intramedullary spinal cord tumors; and out of these, intramedullary epidermoid lesions within the cervical spinal cord are even rarer. Here, we present the case of an adult patient with an infected intramedullary epidermoid cyst, identified on magnetic resonance imaging (MRI) at the C7–D1 level that was successfully excised without any worsening of neurological status.

Case Presentation A 23-year-old female patient presented with history of moderate degree intermittent fever followed by gradually progressive right-sided weakness. She had paresthesia below C5 dermatome on the right side. On close inspection of 
the back, a tiny sinus opening was noted at the D2 level near the midline. MRI of the spine showed an intramedullary lesion at the C6–D1 level with the tract connecting to the subcutaneous lesion. Somatosensory evoked potential (SSEP) monitoring was done during the surgery with near total excision of the lesion.

Conclusion Even though the location is rare, a differential diagnosis of the epidermoid should always be considered. A tiny dermal sinus opening helped us in proper diagnosis, along with surgical excision, by providing us a direct path to the intramedullary lesion. An early diagnosis and treatment with neurophysiological monitoring helped us in the maximum safe resection of the lesion without developing any new deficit.

Spinal intramedullary epidermoid cysts: Three case presentations and literature review

Background:

True intramedullary epidermoid cysts (IECs) not associated with congenital anomalies or previous spinal procedures are extremely rare. In a review of the literature since 1992, only 29 such cases have been reported. Here, we add three new cases in this category.

Case Description:

Three adults presented with spastic paraparesis attributed to thoracic IECs. Gross total microsurgical removal was achieved in two cases, while one case was a partial resection due to capsular adherence to the cord. In all three cases, patients sustained complete recoveries of neurological function and remained symptom free for an average of 5 years follow-up.

Conclusion:

IECs are rare lesions; here, the three located in the thoracic spine, contributed to slow, progressive spastic paraparesis with/without incontinence, and resolved following total (2 patients) and partial (1 patient) resection.

A Case of Scheuermann’s Disease Co-Occurrence with Idiopathic Scoliosis and Intradural-Extramedullary Epidermoid Cyst: The First Case Report in Literature

Background and importance: Scheuermann’s disease (SD), intradural-extramedullary epidermoid cysts and idiopathic scoliosis (IS) are all rare conditions. The co-occurrence of the three condition on one case has not been reported in literature before. We describe an extremely rare case of SD co-occurrence with IS and intradural-extramedullary epidermoid cyst, which is the first in the literature. Clinical presentation: A 13-year old boy and his parents presented at Honghui Hospital complaining of progressive hyperkyphosis for 5 years and back pain for 2 months. Thorough medical examination and radiology confirmed the diagnosis of SD kyphosis, IS, and intradural-extramedullary epidermoid cyst. Medical panel with spine surgeons, oncologists, neurosurgeons, histopathologists and radiologists were consulted. Tumor excise, kyphosis recorrection and spine reconstruction surgery was conducted. Postoperative histological examination detected desquamation of keratin from the epithelial lining and stratified squamous epithelium without skin adnexa. The boy was ambulant 2 days postoperative with walking aids. Conclusion: This is the first case report of Scheuermann’s disease (SD) co-occurrence with idiopathic scoliosis (IS) and intradural-extramedullary epidermoid cyst. The co-occurrence of intradural epidermoid cyst, SD and IS might not be a coincidence, indicating a kind of genetic etiology need to be illuminated.

Formation of de Novo Symptomatic Premedullary Arachnoid Cyst in Adult

BACKGROUND

Intracranial de novo arachnoid cysts in adults are rare, suggesting the involvement of head trauma and inflammatory diseases. We report a symptomatic adult case of nontraumatic de novo arachnoid cyst on the ventral medulla oblongata.

CASE DESCRIPTION

A 56-year-old man came to our hospital complaining of dysphagia and writing difficult since 3 months ago. There was no history of head injury or inflammatory disease. A 25-mm cystic lesion was found on the ventral side of the medulla oblongata on brain magnetic resonance imaging, and the lower cranial nerve and medulla oblongata were highly compressed. The lesion did not exist on magnetic resonance imaging performed 9 years ago. Capsular resection was performed, and the histologic diagnosis was a typical arachnoid cyst. After the operation, all neurologic symptoms disappeared and no recurrence has been observed after 6 months.

CONCLUSIONS

The pathophysiology of nontraumatic de novo arachnoid cysts has many unknown features, and it appears necessary to accumulate further case reports.

Dorsal Spinal Intradural Intramedullary Epidermoid Cyst: A Rare Case Report and Review of Literature

Epidermoid cysts are commonly seen intracranial lesions but their occurrence in the spine is rare. They account for <1% of all the benign tumors of the spine. These are benign epithelial-lined cysts filled with keratin. They are classified into two types: congenital or acquired. Congenital epidermoid cysts are more commonly associated with spinal dysraphic states such as syringomyelia, dermal sinus and spina bifida whereas the acquired cysts are associated with repeated lumbar punctures. Based on the location, they can be extradural, intradural, extramedullary, or intramedullary. Most of the epidermoids are intradural extramedullary. Intramedullary epidermoid cysts are very uncommon. We report a case of a 6-year-old female patient with dorsal epidermoid cyst with neurological deficits. Magnetic resonance imaging of the spine showed a well-defined lesion from D9 to D12 which was hypointense on T1W1 and heterogeneously hyperintense on T2W2. Surgery was performed to excise the lesion and to decompress the spinal cord. Histopathological examination of the excised lesion confirmed it as an epidermoid cyst.

An Epidermoid Cyst of the Thoracic Spine in an Elderly Patient

BACKGROUND

Spinal epidermoid cysts are very rare tumors, especially in the thoracic spine; they represent 0.8% of all spinal epidermoids. In adult cases, they are often associated with surgical procedures such as lumbar puncture. We report a rare case of spinal epidermoid cyst in the thoracic spine of an elderly patient who had never undergone lumber puncture, thoracic spinal surgery, or trauma.

CASE DESCRIPTION

A 78-year old woman presented with a 1-month history of rapidly progressive impairment of sensation in both the lower limbs, with gait disturbance. She had no history of spinal surgery, trauma, or lumbar puncture. Her past medical history was unremarkable. Magnetic resonance imaging of the whole spine revealed an intraspinalextramedullary tumor at the Th 1-2 level. Diffusion-weighted imaging revealed significant homogeneous high intensity. We performed complete resection without damaging the spinal cord or nerve roots. The final histological examination indicated epidermoid cyst without malignancy. Her gait disturbance was completely resolved at 4-month follow-up.

CONCLUSIONS

Epidermoid cysts must be considered among spinal tumors in elderly patients. Early detection by diffusion-weighted imaging and complete resection may lead to good neurological outcome.

Adult intramedullary epidermoid cyst without spinal dysraphism: A case report

Background:

Intramedullary epidermoid cyst (IEC), typically associated with spinal dysraphism, is rare, with fewer than 80 such cases reported in the literature. Here we present an adult with an IEC without spinal dysraphism.

Case Description:

A 41-year-old female presented with the gradual onset of a progressive spastic paraparesis attributed to a magnetic resonance imaging (MRI)-documented D8-9 intramedullary lesion. Following microsurgical excision of the IEC, she fully recovered.

Conclusion:

IECs are rare lesions, typically found in conjunction with spinal dysraphism. Utilizing MRI studies to document the lesion location, gross total microsurgical excision is the procedure of choice. Early excision of these benign lesions maximizes functional recovery.

Surgically Treated de Novo Cervicomedullary Arachnoid Cyst in Symptomatic Adult Patient

BACKGROUND

Arachnoid cysts are a relatively common finding in adult patients, especially with the advent of advanced imaging techniques. The overall incidence ranges from 1%-2%, and the majority are clinically silent. Arachnoid cysts are postulated to arise by congenital anomalies or trauma. De novo formation of arachnoid cysts has been reported but is exceptionally rare and mostly found in the pediatric population after head trauma. There have only been 2 reported cases of symptomatic de novo arachnoid cyst formation in adult patients to date, both with histories of head trauma.

CASE DESCRIPTION

We present a case of a 71-year-old male patient with progressive vertigo who had previous brain magnetic resonance imaging studies without abnormalities. Another MRI was performed 3 years from the last study that showed interval development of a large cystic lesion compressing the right cervicomedullary junction, as well as radiologic evidence of neurosarcoidosis. Intraoperative findings showed a cystic mass with clear, gelatinous fluid. The cyst was drained, and the walls were resected and sent to pathology. Histopathologic testing confirmed the lesion was an arachnoid cyst. The patient's vertiginous symptoms improved after surgery.

CONCLUSIONS

This case represents the first incidence of a pathology-proven, nontraumatic de novo arachnoid cyst.

[Spinal cord epidermoid cysts]

The article describes in detail a large modern clinical series of patients operated on for spinal cord epidermoid cysts.

AIM

the study aim was to comprehensively investigate the epidemiological and clinical peculiarities of spinal cord epidermoid cysts and evaluate immediate and long-term results of their surgical treatment.

MATERIAL AND METHODS

We describe and analyze surgical outcomes of 20 patients with spinal cord epidermoid cysts. This sample was selected from 554 patients with intramedullary tumors and 365 patients with spinal dysraphism (aged from 2 months to 72 years) who were operated on by the first author in 2002-2017.

RESULTS

Our findings confirm a high efficacy and low risk of surgical treatment of patients diagnosed with spinal epidermoid cysts. Severe complications of disease progression serve as indications for 'preventive' surgery even in asymptomatic cases. Complete resection of the tumor capsule without deterioration of the functional surgical result is the main goal of surgical treatment. Incomplete resection is associated with a high risk of recurrence. The most thorough follow-up with annual MRI examination is necessary for the first 6 years after surgery.

Novel combination of paraspinal keyhole surgery with a tubular retractor system leads to significant improvements in lumbar intraspinal extramedullary schwannomas

The aim of the present study was to investigate the efficacy of combining paraspinal keyhole surgery with a tubular retractor system for the microsurgical removal of lumbar intraspinal extramedullary schwannomas. A retrospective analysis was conducted of 56 patients with lumbar intraspinal extramedullary schwannomas who were treated using the microsurgical paraspinal keyhole approach with a tubular retractor system. The mean ± standard deviation was calculated for the following parameters: Surgery time (96.21±14.64 min), hemorrhagic volume (28.54±9.72 ml), bed rest (2.55±0.5 days) and hospital stay (5.68±0.72 days). Two patients presented with cerebrospinal fluid leakage and one patient exhibited a nerve root injury. At a 6-month follow-up visit, postoperative Japanese Orthopedic Association (JOA) and visual analog scale (VAS) scores were evaluated. The mean ± standard deviation JOA scores were 12.00±2.07 for preoperative, 14.73±2.05 for 1 week postoperative, 20.07±2.32 for 3 months postoperative and 21.75±2.18 for 6 months postoperative. The improvement rate was 16.07, 47.48 and 59.77%, respectively. The mean ± standard deviation VAS scores were 6.64±1.31 for preoperative, 3.82±1.51 for 1 week postoperative, 2.11±1.17 for 3 months postoperative and 1.50±1.51 for 6 months postoperative. The JOA and VAS scores improved significantly (P<0.05). Magnetic resonance imaging and computed tomography were performed preoperatively, immediately following surgery and at the 6-month postoperative visit to confirm the efficacy of the resections and evaluate spinal stability. No residual tumors were identified at follow-up. No alterations in the stability of the spine were observed postoperatively. The combination of the microsurgical paraspinal keyhole approach with the tubular retractor system was successful in treating lumbar intraspinal extramedullary schwannomas. The surgical approach was associated with decreased hemorrhages, decreased duration of hospital stay, faster recovery and improved postoperative maintenance of spinal stability.

Thoracic Intradural-Extramedullary Epidermoid Tumor: The Relevance for Resection of Classic Subarachnoid Space Microsurgical Anatomy in Modern Spinal Surgery. Technical Note and Review of the Literature

BACKGROUND

Intradural epidermoid tumors of the spinal cord are commonly associated with spinal cord dysraphism or invasive procedures. We report the particular relationships between spinal subarachnoid compartments and thoracic intradural-extramedullary epidermoid tumor, highlighting the relevant anatomic changes that may influence microsurgery.

METHODS

A 40-year-old woman from compressive myelopathy owing to a thoracic epidermoid tumor extending from T3 to T4 and not associated with spina bifida, trauma, previous surgery, or lumbar spinal puncture underwent microsurgical excision. Accurate tumor membrane dissection, respecting spinal arachnoidal compartments, was performed. Reposition of a laminoplasty plateau helped in restoring thoracic spine anatomic integrity.

RESULTS

Safe gross total tumor resection was achieved. Complete neurologic recovery as well as absence of recurrent tumor was documented at 4-year follow-up. A literature review revealed only 2 other cases of "isolated" thoracic spine epidermoid tumor. However, description of the relationship between tumor membranes and spinal subarachnoid compartments was not available in either case.

CONCLUSIONS

A thorough knowledge of spinal subarachnoid space anatomy is helpful to distinguish between tumor membranes and arachnoidal planes and to achieve a safe and complete resection to avoid recurrences.

Intramedullary epidermoid cysts in adults: Case report and updated literature review

Epidermoid cysts are classical tumors in neurosurgery, but spinal locations are rare and intramedullary locations represent only approximately 80 cases in the literature. Intramedullary epidermoid cysts arise from ectodermic tissue inclusion during neural tube closure. Intramedullary epidermoid cysts are more frequent in young patients and in a thoracic location. We report the case of a 61-year-old patient consulting for bilateral asymmetrical progressive paraparesis and proprioceptive ataxia revealing a T3-T4 exophytic medullar epidermoid cyst. The tumor was surgically removed with a favorable outcome. The capsule was partially removed. The authors present an updated literature review of intramedullary epidermoid cyst diagnosis, management and recommendations.

A New Classification for Pathologies of Spinal Meninges—Part 2: Primary and Secondary Intradural Arachnoid Cysts

BACKGROUND: Spinal intradural arachnoid cysts are rare causes of radiculopathy or myelopathy. Treatment options include resection, fenestration, or cyst drainage.

OBJECTIVE: To classify intradural spinal arachnoid cysts and present results of their treatment.

METHODS: Among 1519 patients with spinal space occupying lesions, 130 patients demonstrated intradural arachnoid cysts. Neuroradiological and surgical features were reviewed and clinical data analyzed.

RESULTS: Twenty-one patients presented arachnoid cysts as a result of an inflammatory leptomeningeal reaction related to meningitis, subarachnoid hemorrhage, intrathecal injections, intradural surgery, or trauma, ie, secondary cysts. For the remaining 109 patients, no such history could be elucidated, ie, primary cysts. Forty-six percent of primary and 86% of secondary cysts were associated with syringomyelia. Patients presented after an average history of 53 ± 88 months. There were 122 thoracic and 7 lumbar cysts plus 1 cervical cyst. Fifty-nine patients with primary and 15 patients with secondary cysts underwent laminotomies with complete or partial cyst resection and duraplasty. Mean follow-up was 57 ± 52 months. In the first postoperative year, profound improvements for primary cysts were noted, in contrast to marginal changes for secondary cysts. Progression-free survival for 10 years following surgery was determined as 83% for primary compared to 15% for secondary cysts. Despite differences in clinical presentation, progression-free survival was almost identical for patients with or without syringomyelia.

CONCLUSIONS: Complete or partial resection leads to favorable short- and long-term results for primary arachnoid cysts. For secondary cysts, surgery can only provide clinical stabilization for a limited time due to the often extensive arachnoiditis.

DWI findings in a iatrogenic lumbar epidermoid cyst. A case report

Epidermoid cysts comprise less than 1% of intraspinal tumors. They can be congenital, frequently associated with other spinal malformations, or iatrogenic, resulting from the implantation of epidermal cells within the spinal canal during the execution of a variety of procedures such as spinal puncture. At MR imaging epidermoid tumors can mimic cystic lesions with fluid content such as arachnoid cysts. DWI can help obtain a correct diagnosis. We describe a case of iatrogenic lumbar epidermoid cyst with DWI findings in a young woman who had undergone epidural anesthesia for Cesarean section three years before the onset of symptoms.

Unusual presentation of congenital dermal sinus: tethered spinal cord with intradural epidermoid and dual paramedian cutaneous ostia

The authors present the first report of spinal congenital dermal sinus with paramedian dual ostia leading to 2 intradural epidermoid cysts. This 7-year-old girl had a history of recurrent left paramedian lumbosacral subcutaneous abscesses, with no chemical or pyogenic meningitis. Admission MRI studies demonstrated bilateral lumbar dermal sinus tracts and a tethered spinal cord. At surgery to release the tethered spinal cord the authors encountered paramedian dermal sinus tracts with dual ostia, as well as 2 intradural epidermoid cysts that were not readily apparent on MRI studies. Congenital dermal sinus should be considered in the differential diagnosis of lumbar subcutaneous abscesses, even if the neurocutaneous signatures are located off the midline.

Microsurgical treatment of spinal epidermoid and dermoid cysts in the lumbosacral region

The aim of this study was to evaluate the characteristics and surgical outcome of spinal epidermoid and dermoid cysts in the lumbosacral spine. We reviewed 26 patients with spinal epidermoid and dermoid cysts (15 epidermoid and 11 dermoid) treated between October 2000 and December 2010. The latter 15 patients of this series underwent neurophysiological monitoring during surgery. Gross total resection of the tumour was achieved in 46.2% of patients, and 53.8% underwent subtotal resection. In 14 patients, the tumour capsule adhered so tightly to the neural structures that a section of the capsule remained in situ. After surgery, the Japanese Orthopaedic Association score improved in 80.8% of patients, remained stable in 15.4%, and declined in 3.8%. The average follow-up period was 53 months. Three patients developed recurrence of the tumour and 20 patients resumed a normal working life. Microsurgical techniques and intraoperative neurophysiological monitoring are practical and reliable methods for radical removal of spinal epidermoid and dermoid cysts that involve the conus medullaris and cauda equina.

Imaging of petrous apex lesions: self-assessment module

The educational objectives for this self-assessment module are for the participant to exercise, self-assess, and improve his or her understanding of the role of imaging in the evaluation of petrous apex lesions.

Cervical intramedullary epidermoid cyst with liquid contents

Intramedullary spinal epidermoid cysts are benign ectopic embryological growths with reported incidence of less than 1% of intramedullary tumors. In this case we report an unusual cervical intramedullary epidermid with liquid contents. A 40-year-old patient presented with progressive weakness of all four limbs of four months duration, bowel and bladder disturbances of two days duration, pain and paresthesias in all four limbs. Magnetic resonance imaging (MRI) revealed a well defined intramedullary lesion extending from C2-C3 level with widening of the cord. The lesion was hypointense on T1W images, hyperintense on T2W and fluid attenuation and inversion recovery images with thin rim of enhancement after contrast administration. Histopathological examination of the excised specimen revealed epidermal lining and keratinous material features of an epidermoid cyst. As in present case, rarely epidermoid cyst can have clear contents, and an MRI finding can closely mimic the features of arachnoid cyst, findings not classical and is different than described in literature.

[Imaging of demyelinating and neoplastic diseases of the spinal cord]

The clinical symptoms of myelopathy are variable and non-specific. Demyelinating as well as neoplastic spinal cord diseases can cause paresthesia, progressive sensomotoric deficits and bowel and bladder dysfunction. Imaging of the spine, especially with magnetic resonance imaging (MRI), is an essential component in the diagnostic assessment of myelopathy and makes a substantial contribution to achieving the correct diagnosis. Although intramedullary neoplasms are far less common than demyelinating spinal cord diseases, radiologists should be familiar with the three most common entities, astrocytoma, ependymoma and hemangioblastoma, which represent over 70% of all spinal cord neoplasms. An early diagnosis and therapy is essential with neoplastic and demyelinating spinal cord diseases to hold residual neurological deficits as low as possible.

Anorectal malformation and spinal dysraphism: the value of diffusion-weighted imaging in detecting associated intradural (epi)dermoid cyst

Anorectal malformations (ARMs) are associated with a variety of spinal dysraphisms, of which clinical impact is often underestimated. A 6-year-old girl, with a history of rectovaginal fistula, presented with gait disturbance, asthenia, and worsening of fecal incontinence. The spinal magnetic resonance imaging (MRI) at 12 months of age had revealed a tethered cord and a little intradural lipoma. Within the lipoma, a small cystic lesion, interpreted as a cerebrospinal fluid (CSF)-filled loculation, was also described. A consecutive MRI showed a marked increase in size of the CSF-like cyst that was clearly hyperintense on diffusion-weighted imaging (DWI) and presented reduced apparent diffusion coefficient values (855 +/- 109 s/mm(2)), not compatible with CSF values. This lesion, interpreted as an (epi)dermoid cyst, was removed and histologically confirmed; the spinal cord was untethered. The child's lower limb motor deficit resolved rapidly after surgery, and the fecal incontinence slowly returned to the previous bowel habit. There is a growing interest in recognizing and defining spinal dysraphism in ARM patients because some abnormalities may carry severe clinical consequences. For this purpose, a standardized MR protocol is required, in which DWI plays a pivotal role to disclose associated dysembriogenetic lesions, in particular when a CSF loculation is detected.

Dorsal intramedullary spinal epidermoid cysts: Report of two cases and review of literature

Intramedullary epidermoid cysts of the spinal cord are rare tumors, especially those not associated with spinal dysraphism. About 50 cases have been reported in the literature. Of these, only seven cases have had magnetic resonance imaging (MRI) studies. We report two cases of spinal intramedullary epidermoid cysts with MR imaging. Both were not associated with spina bifida. In one patient, the tumor was located at D4 vertebral level; while in the other, within the conus medullaris. The clinical features, MRI characteristics and surgical treatment of intramedullary epidermoid cyst are presented with relevant review of the literature.