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Summary Aquatic larvae are known in three early branches of Pterygota: Ephemeroptera (mayflies), Plecoptera (stoneflies), and Odonata (dragonflies, damselflies). A common origin of these larvae has been suggested, yet also counterarguments have been put forward, for example, the different position of larval gills: laterally on the abdomen in Ephemeroptera, terminally in Odonata, variably in Plecoptera. We discuss recent fossil findings and report a new dragonfly-type larva from Kachin amber (Myanmar), which possesses ancestral characters such as a terminal filum, maintained in ephemeropterans, but lost in modern odonatan larvae. The new larva possesses lateral protrusions on the abdominal segments where in other lineages gills occur. Together with other fossils, such as a plecopteran retaining lateral gills on the abdomen, this indicates that lateral protrusions on the abdomen might have well been an ancestral feature, removing one important argument against the idea of an aquatic larva in the ground pattern of Pterygota., Graphical abstract, Highlights • A new dragonfly-type larva was found in Kachin amber (Myanmar, 99 million years old). • The larva possesses a terminal filum, which is not known in modern dragonfly larvae • It also exhibits lateral abdominal protrusions where in other lineages gills occur • This find makes an aquatic larva in the ground pattern of Pterygota more likely, Paleontology; Entomology; Evolutionary history; Paleobiology

Objective: Myxopapillary ependymomas (MPEs) in children are rarely reported low-grade glial tumors; however, MPEs sometimes possess malignant characteristics such as spinal seeding/drop metastasis (SSM). We aimed to present 3 pediatric MPE cases that experienced SSM at 2 neurosurgical centers. Materials and Methods: We retrospectively reviewed the medical records of 38 primary spinal MPE cases who underwent surgery at 2 neurosurgical centers spanning 16 years, from 2004 to 2019. All pediatric cases (patient age Results: Three pediatric MPE cases (2 females and 1 male) experienced SSM. The mean age at first presentation was 12.0 ± 1.0 years. The mean preoperative course was 2.9 ± 1.2 months. The predominant location was the lumbar spine in 2 tumors (both originated from terminal filum [TF]). Two tumors were located intradural intramedullary. Gross-total resection was achieved in 2 patients. No patient had neurofibromatosis type 2. No adjuvant treatment was given after the first surgery. The mean period between the first diagnosis and diagnosis of SSM was 44.0 ± 31.5 months. The location of SSM in all patients was the sacral spine (1 patient experienced distant metastasis in her brain besides her sacral metastasis). The mean follow-up was 68.3 ± 53.7 months. Conclusions: We found a statistically significant relationship between SSM in pediatric MPEs and the intramedullary location, TF origin, and number of affected segments. Close clinical and radiological follow-up is essential for pediatric MPE patients.

Object The pathophysiology of occult tethered cord syndrome (OTCS) with no anatomical evidence of a caudally shifted conus and a normal terminal filum is hard to understand. Therefore, the diagnosis of OTCS is often difficult. The authors hypothesized that the posterior displacement of the terminal filum may become prominent in patients with OCTS who are in a prone position if filum inelasticity exists, and they investigated prone-position MRI findings. Methods Fourteen patients with OTCS and 12 control individuals were examined using T2-weighted axial MRI with the patients in a prone position on a flat table. On each axial view, the distance between the posterior and anterior ends of the subarachnoid space (A), the distance between the posterior end of the subarachnoid space and the terminal filum (B), the distance between the posterior end of the subarachnoid space and the dorsal-most nerve among the cauda equina (C), and the distance between the posterior end of the subarachnoid space and the ventral-most nerve (D) were measured. The location ratios of the terminal filum, the dorsal-most nerve, and the ventral-most nerve were calculated by the ratio of A to B (defined as TF = B/A), A to C (defined as DN = C/A), and A to D (defined as VN = D/A), respectively. Patients underwent sectioning of the terminal filum with the aid of a surgical microscope. The low-back pain Japanese Orthopaedic Association score was obtained before surgery and at the final follow-up visit. Results On prone-position axial MRI, the terminal filum was separated from the cauda equina and was shifted caudally to posterior in the subarachnoid space in all patients with OTCS. The locations of the caudal cauda equina shifted to ventral in the subarachnoid space. The TF values in the OTCS group were significantly lower than those in the control group at the L3–4 (p = 0.023), L-4 (p = 0.030), L4–5 (p = 0.002), and L-5 (p < 0.001) levels. In contrast, the DN values in the OTCS group were significantly higher than those of the control group at the L-2 (p = 0.003), L2–3 (p = 0.002), L-3 (p < 0.001), L3–4 (p < 0.001), L-4 (p = 0.007), L4–5 (p = 0.003), and S-1 (p = 0.014) levels, and the VN values in the OTCS group were also significantly higher than those of the control group at the L2–3 (p = 0.022), L-3 (p = 0.027), L3–4 (p = 0.002), L-4 (p = 0.011), L4–5 (p = 0.019), and L5–S1 (p = 0.040) levels. Sections were collected during surgery for histological evaluation, and a decreased elasticity within the terminal filum was suggested. Improvements in the Japanese Orthopaedic Association score were observed at the final follow-up in all patients. Conclusions The authors' new method of using the prone position for MRI shows that the terminal filum is located significantly posterior and the cauda equina is located anterior in patients with OTCS, suggesting a difference in elasticity between the terminal filum and cauda equina.

✓Spinal lipomas, particularly lipomas of the conus medullaris and terminal filum, are the most common form of occult spinal dysraphism and represent a wide spectrum of disease with regard to anatomy, clinical presentation, and treatment options. These lesions, however, are united by a similar embryology and pathological mechanism by which symptoms arise.Recently, the treatment of these lesions has generated much controversy, with some physicians advocating surgical treatment for all patients regardless of symptoms and others proposing that surgery be withheld until symptoms develop. The authors discuss lumbosacral spinal lipomas, with particular attention to the theories of their origin, anatomical and pathological features, and treatment options, including a review of current controversies.

✓The concept of an occult tethered cord syndrome (OTCS), in which a normally located conus is tethered by the terminal filum, is controversial. Children with OTCS typically present with neurogenic urinary incontinence that has been refractory to medical management. Authors of a number of case series have suggested that section of the terminal filum may improve urinary symptoms, but the quality of the evidence supporting this treatment is not good. The literature related to OTCS is reviewed and the progress toward a randomized controlled trial to assess the value of filum section in OTCS is detailed. A scientific answer to the question of filum section for OTCS awaits the results of an ongoing pilot randomized controlled trial and a more definitive trial to follow.

Object Children with spina bifida occulta require early surgery to prevent neurological deficits. The treatment of patients with a congenitally tethered cord who present in adulthood remains controversial. Methods The authors studied the medical records of 61 adult patients who underwent surgical untethering for spina bifida occulta at three institutions between 1994 and 2003. Patients who had undergone prior myelomeningocele repair or tethered cord release surgery were excluded. The most common intraoperative findings were lipomyelomeningocele (41%) and a tight terminal filum (36%). The follow-up duration ranged from 10.8 to 149.5 months. Of the 34 patients with back pain, status improved in 65%, worsened in 3%, remained unchanged in 18%, and improved and later recurred in 15%. Lower-extremity pain improved in 16 patients (53%), remained unchanged in 23%, improved and then recurred in 17%, and worsened in 7%. Lower-extremity weakness improved in 47%, remained unchanged in 47%, and improved and then recurred in 5%. Finally, of the 17 patients with lower-extremity sensory changes, status improved in 35%, remained unchanged in 35%, and the information on five patients was unavailable. Surgical complications included three wound infections, one cerebrospinal fluid leak, and two pseudomeningoceles requiring surgical revision. One patient developed acute respiratory distress syndrome and sepsis postoperatively and died several days later. Conclusions Adult-age presentation of a congenital tethered cord is unusual. Despite a slight increase in postoperative neurological injury in adults, surgery has relatively low risk and offers good potential for neurological improvement or stabilization. As they do in children, the authors recommend early surgery in adults with this disorder. The decision to undertake surgery, however, should be modulated by other factors such as a patient's general medical condition and risk posed by anesthesia.

(N. R. Selden) Object Controversy exists regarding proper indications for surgical lysis of the terminal filum in children with voiding dysfunction and tethered spinal cord. Recently, surgery has been offered to children who have a normally positioned conus medullaris and no terminal filum abnormality visible on 1.5-tesla magnetic resonance images (referred to as minimal or occult tethered cord syndrome [TCS]). The author evaluates existing clinical and scientific evidence relevant to this controversy. Methods Five retrospective, observational, noncontrolled studies of surgical terminal filum lysis for occult TCS in children were identified. Two further studies in which the authors reported surgical results in children with a normal-level conus medullaris were also identified. Conclusions These studies document encouraging clinical outcomes following surgery. Clinicopathological evidence suggests that occult TCS may result from radiographically occult structural abnormalities of the terminal filu...

Controversy exists regarding proper indications for surgical lysis of the terminal filum in children with voiding dysfunction and tethered spinal cord. Recently, surgery has been offered to children who have a normally positioned conus medullaris and no terminal filum abnormality visible on 1.5-tesla magnetic resonance images (referred to as minimal or occult tethered cord syndrome [TCS]). The author evaluates existing clinical and scientific evidence relevant to this controversy.Five retrospective, observational, noncontrolled studies of surgical terminal filum lysis for occult TCS in children were identified. Two further studies in which the authors reported surgical results in children with a normal-level conus medullaris were also identified.These studies document encouraging clinical outcomes following surgery. Clinicopathological evidence suggests that occult TCS may result from radiographically occult structural abnormalities of the terminal filum. Although a preponderance of Class III clinical evidence supports the use of surgical filum lysis to treat occult TCS, no Class I or II evidence exists. Clinical practice varies; therefore, performance of a prospective randomized clinical trial of surgical terminal filum lysis for the treatment of occult TCS is advocated.

✓ The authors describe a patient with neurological symptoms caused by a carcinoid tumor at the terminal filum without carcinoid “flushing” syndrome or endocrinological abnormalities. The patient underwent subtotal resection and adjuvant radiotherapy. Extensive postoperative workup revealed no primary site of disease. To the authors' knowledge, this patient represents the first case of terminal filum carcinoid tumor.

The proposed normal function of the terminal filum of the spinal cord is to fixate, stabilize and buffer the distal cord from normal and abnormal cephalic and caudal traction. The filum is a viseoelastic band that usually allows the conus medullaris to move slightly during flexion and extension of the spine. It is theorized that if the viscoelasticity of the filum is lost or compromised by fatty infiltration [1] or abnormal thickening, then caudal tension and traction may cause stress upon the conus, resulting in a tethered spinal cord (TSC).

Object The author describes the paucity of information known about occult tethered cord syndrome and summarizes the argument for using a nonsurgical approach in these cases. Methods A review of what we do and do not know about this syndrome is provided. Surgical procedures to divide the terminal filum in patients with symptoms of tethered spinal cord without the imaging correlates are said to result in clinical improvement, yet there is little physiological evidence to support the surgical release of the filum in the absence of other anatomical lesions. Validated diagnostic and outcome measures are also lacking, which makes the interpretation of reported results exceedingly difficult. Finally, reports used to support surgical intervention are limited by small size, the absence of control groups, and observer bias. Conclusions Without conclusive clinical evidence, the arguments supporting surgery for occult tethered cord syndrome must be viewed cautiously.

Object The filum terminale externum (FTE) is the extradural component of the filum terminale internum and little attention has been dedicated to this structure in the literature. The authors theorized that the rare intrasacral ependymomas may originate from ependymal cell collections within the FTE. Methods To address this hypothesis, the FTE was dissected and analyzed histologically in 15 adult cadavers. None of the specimens was found to harbor ependymal or other glial cell collections. Conclusions The authors found previously undescribed smooth-muscle cells within the FTE. Furthermore, histological analysis identified adipose, nerve, bone, and cartilage cells.

✓The authors report on a child with a composite type of split cord malformation (SCM). The patient presented with symptoms of a common cold. The diagnosis of SCM was made based on computerized tomography and magnetic resonance (MR) imaging of whole spinal axis. The SCM was Type I at T-4 and T-5 and Type II at T-12, according to the classification developed by Pang. The child underwent resection of the splitting lesions and terminal filum release. No case of composite-type SCM reported to date contains documentation of such a malformation. Because of the possible neurological and urological problems, the authors recommend MR imaging of the whole spine be performed during an evaluation for SCM.

✓ Myxopapillary ependymomas represent the most frequent type of ependymomas found at the conus medullaris—cauda equina-terminal filum level. They are neuroectodermal tumors mainly observed during the fourth decade of life. Pediatric cases have been rarely described at an age range of 10 to 13 years. Myxopapillary ependymomas are typically solitary tumors involving the terminal filum. Simultaneous discovery of two tumors located both on the terminal filum has been reported once. The pathogenesis of this focal ependymoma located at the same embryological level, on the terminal filum, is uncertain; it may represent one end of a spectrum, the other end being the giant ependymoma of the terminal filum.

The authors report one case of cauda equina paraganglioma and review the neurosurgical, radiological and pathological literatureon this rare tumour. Although it is difficult to distinguish preoperatively the paraganglioma from other tumours of the cauda equina, like neurinoma or ependymoma, this neuroendocrine tumour should be included in differential diagnosis.