Abstract

Background:The tethered cord syndrome (TCS) accompanying Chiari-1 (CM-1) malformations and the occult tethered cord syndrome (OTCS) syndrome accompanying the low lying cerebellar tonsil (LLCT) syndrome may be treated with sectioning of the filum terminale (SFT).

Methods:Utilizing PubMed, we reviewed the neurosurgical literature to determine how frequently spinal neurosurgeons diagnosed the TCS (e.g., conus terminating below the normal L1-L2 disc level) on lumbar magnetic resonance (MR) studies in patients with CM-1 malformations [e.g. tonsils >5–12 mm below the foramen magnum (FM) warranting SFT]. In addition, we assessed how frequently spinal neurosurgeons encountered the OTCS (e.g., conus normally located at L1-L2 on MR) accompanying the LLCT (e.g., tonsils herniated

Results:According to the neurosurgical literature, the incidence of TCS accompanying CM-1 requiring SFT ranged from 2.2% to

Conclusions:Given the differences in the literature, more studies are needed to assess the risks (complications) vs. benefits (improved neurological outcomes) of SFT surgery for TCS with CM-1 and SFT for OCTS with LLCT.

Keywords: Chiari-1 malformations, definitions, indications, low lying cerebellar tonsil syndrome, occult tethered cord syndrome, prevalence, section of filum terminale, tethered cord syndrome

INTRODUCTION

Utilizing PubMed, we reviewed the neurosurgical literature regarding the prevalence of the tethered cord syndrome (TCS) with Chiari-1 malformations (CM-1) requiring sectioning of the filum terminale (SFT). Additionally, we assessed how often the occult tethered cord syndrome (OCTS) was correlated with the low lying cerebellar syndrome (LLCT) also warranting SFT. Further, we asked how frequently the TCS, defined on magnetic resonance (MR) by the conus located below the L1-L2 level, correlated with CM-1 (tonsils >5 mm–12 mm below the foramen magnum FM), and with the LLCT [tonsils herniated < 5 mm below the FM on MR] [Tables 1 and 2 ]. Further, we queried how often the OCTS, defined on MR by the normal conus location at the L1-L2 level, corresponded with the LLCT (tonsils herniated <5 mm below the FM on MR) [Tables 1 and 2 ].

Table 1

Definitions of normal tonsil location, chiari-1 malformations, and low lying cerebellar tonsil syndrome

Table 2

Tethered cord and occult tethered cord syndrome with Chairi-1 Malformations and low lying cerebellar tonsil syndrome

DEFINITIONS OF NORMAL TONSIL LOCATION VERSUS CHIARI-1 MALFORMATIONS

Normally, the cerebellar tonsils are located 2.9 mm ± 3.4 mm above or up to 3 mm below the FM [ Table 1 ].[ 1 ] Borderline CM-1 are defined by the tonsils located between 3 and 5 mm below the FM [ Table 1 ].[ 1 ] According to the neurosurgical literature, CM-1 are typically defined on MR scans by a >5 mm of tonsillar descent below the FM e.g.,[ 1 2 4 8 ]

FREQUENCIES OF CHIARI-1 MALFORMATIONS IN ADULTS AND CHILDREN

Different frequencies of CM-1 have been reported in the adult and pediatric age groups [Tables 1 and 2 ].[ 4 8 6 9 ] In 2000, Meadows et al. reviewed 22,591 MR studies (over 43 months); only 0.78% (175 patients) had CM-1 malformations (e.g. tonsils >5 mm below FM) [ Table 1 ].[ 4 ] Using this definition, in 1999, Milhorat et al. diagnosed CM-1 in 332 patients, and in 2009, diagnosed CM-1 in 2987 patients [Tables 1 and 2 ].[ 6 8 ] In 2018, Passias et al. found the increased diagnosis of CM-1 in the pediatric population from 45 to 96 per 100,000 [e.g. 5432 Kid Database (2003–2012)], in patients averaging 10.5 years of age (range, 0–20) [ Table 2 ].[ 9 ]

SYMPTOMATIC CHIARI-1 MALFORMATIONS

According to the literature, the onset of symptoms correlated with differing degrees of CM-1 tonsillar herniation [ Table 1 ].[ 1 2 4 ] In the study by Aboulezz et al., CM-1 patients became symptomatic once the MR demonstrated an average of 10.3 ± 4.5 mm (13 patients) of tonsillar herniation below the FM.[ 1 ] In the study by Elster et al., out of 68 patients with CM-1, 70% were symptomatic when the tonsils were 5–10 mm below the FM, while 100% were symptomatic with tonsils >12 mm below the FM [ Table 1 ].[ 2 ] In 2000, Meadows found only 175 CM-1 malformations (0.78%) out of 22,591 MR studies performed; nevertheless, only 25 (14% of the 175) were symptomatic from tonsils averaging 11.4 mm ± 4.86 mm below the FM [ Table 1 ].[ 4 ]

DEFINITION AND FREQUENCY OF THE LOW LYING CEREBELLAR TONSIL SYNDROME (LLCT)

The neurosurgical literature revealed few references to the LLCT [ Table 1 ].[ 6 8 ] Milhorat et al. in 1999 found 34 patients with MR-documented tonsils <5 mm below the FM who exhibited “Chiari-1 like” clinical syndromes; this led to their definition of the LLCT [ Table 1 ].[ 8 ] In 2009, Milhorat et al. evaluated 2987 patients with CM-1, and identified another 289 (9.7%) patients with LLCT.[ 6 ]

ANOMALIES ASSOCIATED WITH ADULT/PEDIATRIC CHIARI-1/LOW LYING CEREBELLAR TONSIL SYNDROME (LLCT)

The neurosurgical literature demonstrated multiple anomalies accompanying the CM-1/LLCT syndromes in adult and pediatric populations [Tables 1 and 2 ].[ 2 7 8 9 ] Several studies defined the following; a 24% incidence of skeletal abnormalities, a 40%-65% frequency of syrinx formation, a 42% incidence of scoliosis, a 12% frequency of basilar invagination, and 12.7% incidence (357 out of 2813 patients with CM-1) with occipital-atlantal hypermobility [hereditary connective tissue disorder (HCTD)/Ehlers–Danlos syndrome (EDS)] [ Table 1 ].[ 2 8 6 ] In Passias et al., pediatric series of 5432 patients with CM-1 (kid database 2003–2012; ages 0–20), 23.8% had accompanying syringomyelia, 11.5% exhibited syringobulbia, and 5.9% had hydrocephalus [ Table 2 ].[ 9 ]

DIFFERENT FREQUENCIES OF TETHERED CORD SYNDROME WITH CHIARI-1

A review of the neurosurgical literature revealed a variable correlation between CM-1 and the TCS (e.g. conus below the L1-L2 disc level on MR) requiring SFT [ Table 2 ].[ 6 9 12 ] In 2009, Milhorat et al. described a 14% incidence of TCS with CM-1 (2987 patients) requiring SFT [ Table 2 ].[ 6 ] Valentini et al., in 2011, evaluating 110 patients with CM-1 malformations, and found a <6% incidence of TCS requiring SFT: they concluded there was no significant correlation between the two [ Table 2 ].[ 12 ] In 2018, Passias et al. reported that, for 5432 children with CM-1 (e.g., kid database, 2003–2012), only 2.2% had associated TCSs; they considered this a minimal correlation at best [ Table 2 ].[ 9 ]

CRANIAL VS. SPINAL DECOMPRESSION VS. FUSION FOR CHIAIR-1 MALFORMATIONS IN THE PEDIATRIC AGE GROUP

In the pediatric neurosurgical literature, the study by Passias et al. (2018) was the most prominent one discussing the successive 2003–2013 frequencies of cranial vs. spinal decompression vs. fusion for CM-1 malformations [ Table 2 ].[ 9 ] They found that, out of 5432 children undergoing surgery for CM-1 malformations, the incidence of cranial decompression decreased from 42.2% to 30%, while the frequency of spinal decompression increased from 73.1% to 77.4%. Over the same period, fusion rates increased from 0.45% to 1.8%, but correlated with more complications (e.g., 11.9% adverse events for fusion vs. 4.7% for decompression alone) [ Table 2 ].

DEFINITION OF THE OCCULT TETHERED CORD SYNDROME (OCTS)

A review of the neurosurgical literature showed that few spinal neurosurgeons highly correlated the OCTS (normal location of the conus at the L1-L2 level on MR) warranting SFT with the LLCT [ Table 2 ].[ 6 ] In 2009, Milhorat et al. observed that, for 289 patients with LLCT (289), there was a 63% frequency of the OTCS (182) warranting SFT [ Table 2 ].[ 6 ] Patients exhibited a clinical “Chiari-like syndrome” attributed in part to the elongation/downward displacement of the hindbrain/cerebellar ectopia, reduced cerebrospinal fluid (CSF) flow in the lumbar theca, and other factors, relieved by SFT.

DIFFERENT FREQUENCIES OF SECTIONING OF THE FILUM TERMINALE FOR OCCULT TETHERED CORD SYNDROME IN PATIENTS WITH CHIARI-1/LOW LYING CEREBELLAR TONSIL SYNDROMES (LLCT)

Multiple studies in the neurosurgical literature summarized the results of SFT performed for OTCS in patients with CM-1/LLCT syndromes [ Table 2 ].[ 3 5 10 ] Metcalfe et al. in 2006 diagnosed 36 pediatric patients with OCTS; this represented just 0.04% of all pediatric urological clinic visits. Signs and symptoms included 83% daytime urological incontinence, 55% reduced bladder capacity, and 47% encopresis [ Table 2 ].[ 5 ] Following SFT, 72% of patients improved, 42% had improved urinary incontinence, 57% had improved urodynamics, and 88% exhibited improved bowel incontinence. Steinbok et al. in 2007 similarly defined OCTS in patients with neurogenic urinary incontinence [ Table 2 ].[ 11 ] In a separate study, they further compared the results of SFT in children with urological symptoms and signs attributed to OCTS. Results of SFT performed in 8 children were compared vs. 7 managed without surgery [ Table 2 ].[ 10 ] Up to 3.1 years postoperatively, 7 of 8 patients undergoing SFT improved (e.g., urodynamic confirmation in 4 patients). Over an average of 3.3 years, of the 7 children treated nonsurgically, 2 had urological improvement, 4 had bilateral ureteric reimplantation, and 1 underwent a delayed SFT 8 years later with improvement. The authors concluded that future randomized controlled studies (RCTs) were required to better document the safety/efficacy of SFT for OCTS. In 2011, Massimi et al. found no correlation between CM-1 and the frequency of the TCS or OTCS syndromes [ Table 2 ].[ 3 ] They could not identify any clinical or experimental evidence to support the “caudal traction theory” for performing SFT in patients with OCTS (e.g., releasing the tethered cord allowing the tonsils to migrate cephalad/ascend). They also concluded that more studies were warranted and that the value of this treatment was “still under debate” [ Table 2 ].

CONCLUSION

Reviewing the neurosurgical literature revealed a 2.2% to <6%, up to a higher 14% frequency of TCS requiring SFT in patients with CM-1 malformations [ Table 2 ].[ 6 9 12 ] Few studies highly correlated the OTCS requiring SFT with the LLCT syndrome [ Table 2 ].[ 6 ] Given the differences in the literature reviewed, further studies are warranted to determine the risks (complications) vs. benefits (improved clinical outcomes) for performing SFT for TCS with CM-1, and OTCS with the LLCT syndrome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

1. Aboulezz AO, Sartor K, Geyer CA, Gado MH. Position of cerebellar tonsils in the normal population and in patients with Chiari malformation: A quantitative approach with MR imaging. J Comput Assist Tomogr. 1985. 9: 1033-6

2. Elster AD, Chen MY. Chiari I malformations: Clinical and radiologic reappraisal. Radiology. 1992. 183: 347-53

3. Massimi L, Peraio S, Peppucci E, Tamburrini G, Di Rocco C. Section of the filum terminale: Is it worthwhile in Chiari type I malformation?. Neurol Sci. 2011. 32: S349-51

4. Meadows J, Kraut M, Guarnieri M, Haroun RI, Carson BS. Asymptomatic Chiari type I malformations identified on magnetic resonance imaging. J Neurosurg. 2000. 92: 920-6

5. Metcalfe PD, Luerssen TG, King SJ, Kaefer M, Meldrum KK, Cain MP. Treatment of the occult tethered spinal cord for neuropathic bladder: Results of sectioning the filum terminale. J Urol. 2006. 176: 1826-9

6. Milhorat TH, Bolognese PA, Nishikawa M, Francomano CA, McDonnell NB, Roonprapunt C. Association of Chiari malformation type I and tethered cord syndrome: Preliminary results of sectioning filum terminale. Surg Neurol. 2009. 72: 20-35

7. Milhorat TH, Bolognese PA, Nishikawa M, McDonnell NB, Francomano CA. Syndrome of occipitoatlantoaxial hypermobility, cranial settling, and Chiari malformation type I in patients with hereditary disorders of connective tissue. J Neurosurg Spine. 2007. 7: 601-9

8. Milhorat TH, Chou MW, Trinidad EM, Kula RW, Mandell M, Wolpert C. Chiari I malformation redefined: Clinical and radiographic findings for 364 symptomatic patients. Neurosurgery. 1999. 44: 1005-17

9. Passias PG, Pyne A, Horn SR, Poorman GW, Janjua MB, Vasquez-Montes D. Developments in the treatment of Chiari type 1 malformations over the past decade. J Spine Surg. 2018. 4: 45-54

10. Steinbok P, Kariyattil R, MacNeily AE. Comparison of section of filum terminale and non-neurosurgical management for urinary incontinence in patients with normal conus position and possible occult tethered cord syndrome. Neurosurgery. 2007. 61: 550-5

11. Steinbok P, MacNeily AE. Section of the terminal filum for occult tethered cord syndrome: Toward a scientific answer. Neurosurg Focus. 2007. 23: E5-

12. Valentini LG, Selvaggio G, Visintini S, Erbetta A, Scaioli V, Solero CL. Tethered cord: Natural history, surgical outcome and risk for Chiari malformation 1 (CM1): A review of 110 detethering. Neurol Sci. 2011. 32: S353-6