Ponticulus posticus

Ponticulus posticus

The ponticulus posticus is a bony bridge in the atlas between the lateral mass and the posterior arch. It results due to ossification of the posterior atlantooccipital ligament of atlas and encloses the vertebral artery and the first cervical nerve root.

It is a normal anatomical variant of atlas vertebrae (C1) and resides in the posterior arch of atlas in relation to the vertebral artery. It is an incidental finding visualised from lateral cephalograms taken for routine orthodontic treatment purposes. Ponticulus posticus in Latin means ‘little posterior bridge’. Other synonyms for ponticulus are arcuate foramen, kimerle anomaly, retroarticular foramen and retocondylar foramen.

An overall incidence of ponticulus posticus has been reported to be 16.7%. Literature reveals a higher incidence in females compared with males and this anomaly was age-independent.

Diagnosis

Failure to detect ponticulus posticus can have grave complications during cervical spine surgical intervention, especially those requiring screw placement in lateral mass region of Atlas vertebra 1).


Consecutive computed tomography scans (n=210) were reviewed for PP and high-riding vertebral artery (HRVA) (defined as an internal height of <2 mm and an isthmus height of <5 mm). In scans with PP+HRVA, we measured the ipsilateral pedicle width, pars length, and laminar thickness and compared them with controls (those without PP or HRVA).

PP was present in 14.76% and HRVA in 20% of scans. Of the 420 sides in 210 scans, PP+HRVA was present on 13 sides (seven right and six left). In scans with PP+HRVA, the length of the C2 par was shorter compared with controls (13.69 mm in PP+HRVA vs. 20.65 mm in controls, p<0.001). The mean C2 pedicle width was 2.53 mm in scans with PP+HRVA vs. 5.83 mm in controls (p<0.001). The mean laminar thickness was 4.92 and 5.48 mm in scans with PP+HRVA and controls, respectively (p=0.209).

The prevalence of PP+HRVA was approximately 3% in the present study. Our data suggest that, in such situations, C2 pedicle width and pars length create important safety limitations for a proposed screw, whereas the translaminar thickness appears safe for a proposed screw 2).


In CT scans some anomalies, such as abnormal facet complex and arch anomalies, have to be differentiated from fractures in a trauma patient. Other anomalies, like PP, have to be looked for during preoperative planning to avoid complications during surgery. Therefore, knowledge of these anomalies is important as different anomalies have different clinical courses and management 3).

Case series

Thirty-three consecutive patients with unstable odontoid fractures underwent Goel technique and Harms technique (C1–2 arthrodesis). Surgery was performed with the aid of lateral fluoroscopy control in 16 cases (control group) that was supplemented by Doppler ultrasonography in 17 cases (Doppler group). Two patients in each group had a C1 ponticulus posticus. In the Doppler group, Doppler probing was performed during lateral subperiosteal muscle dissection, stepwise drilling, and tapping. Blood flow velocity in the V3 segment of the VA was recorded before and after posterior arthrodesis. All patients had a 12-month outpatient follow-up, and the outcome was assessed using the Smiley-Webster Pain Scale. Neither VAI nor postoperative neurological impairments were observed in the Doppler group. In the control group, VAIs occurred in the 2 patients with C1 ponticulus posticus. In the Doppler group, 1 patient needed intra- and postoperative blood transfusions, and no difference in terms of Doppler signal or VA blood flow velocity was detected before and after C1-C2 posterior arthrodesis. In the control group, 3 patients needed intra- and postoperative blood transfusions.Useful in supporting fluoroscopy-assisted procedures, intraoperative Doppler may play a significant role even during surgeries in which neuronavigation is used, reducing the chance of a mismatch between the view on the neuronavigation screen and the actual course of the VA in the operative field and supplying the additional data of blood flow velocity 4).

References

1)

Elliott RE, Tanweer O. The prevalence of the ponticulus posticus (arcuate foramen) and its importance in the Goel-Harms procedure: meta-analysis and review of the literature. World Neurosurg. 2014 Jul-Aug;82(1-2):e335-43. doi: 10.1016/j.wneu.2013.09.014. Epub 2013 Sep 18. Review. PubMed PMID: 24055572.
2)

Kothari MK, Dalvie SS, Gupta S, Tikoo A, Singh DK. The C2 Pedicle Width, Pars Length, and Laminar Thickness in Concurrent Ipsilateral Ponticulus Posticus and High-Riding Vertebral Artery: A Radiological Computed Tomography Scan-Based Study. Asian Spine J. 2019 Apr;13(2):290-295. doi: 10.31616/asj.2018.0057. Epub 2018 Dec 7. PubMed PMID: 30521747; PubMed Central PMCID: PMC6454277.
3)

N V A, Avinash M, K S S, Shetty AP, Kanna RM, Rajasekaran S. Congenital Osseous Anomalies of the Cervical Spine: Occurrence, Morphological Characteristics, Embryological Basis and Clinical Significance: A Computed Tomography Based Study. Asian Spine J. 2019 Mar 14:535-543. doi: 10.31616/asj.2018.0260. [Epub ahead of print] PubMed PMID: 30866614; PubMed Central PMCID: PMC6680038.
4)

Lofrese G, Cultrera F, Visani J, Nicassio N, Essayed W, Donati R, Cavallo MA, De Bonis P. Intraoperative Doppler ultrasound as a means of preventing vertebral artery injury during Goel and Harms C1-C2 posterior arthrodesis: technical note. J Neurosurg Spine. 2019 Aug 16:1-7. doi: 10.3171/2019.5.SPINE1959. [Epub ahead of print] PubMed PMID: 31419805.

Medical student

Medical student

For students beginning their medical education, the neuroscience curriculum is frequently seen as the most difficult, and many express an aversion to the topic. A major reason for this aversion amongst learners is the perceived complexity of neuroanatomy 1).

Osler created the first residency program for specialty training of physicians, and he was the first to bring medical students out of the lecture hall for bedside clinical training. Historically, medical student education in neurological surgery has generally limited student involvement to assisting in research projects with minimal formal clinical exposure before starting sub-internships and application for the neurosurgery match. Consequently, students have generally had little opportunity to acquire exposure to clinical neurosurgery and attain minimal proficiency 2).

Neurosurgery seeks to attract the best and brightest medical students; however, there is often a lack of early exposure to the field, among other possible barriers.

United States

Lubelski et al. sought to identify successful practices that can be implemented to improve medical student recruitment to neurosurgery.

United States neurosurgery residency program directors were surveyed to determine the number of medical student rotators and medical students matching into a neurosurgery residency from their programs between 2010 and 2016. Program directors were asked about the ways their respective institutions integrated medical students into departmental clinical and research activities.

Complete responses were received from 30/110 institutions. Fifty-two percent of the institutions had neurosurgery didactic lectures for 1st- and 2nd-year medical students (MS1/2), and 87% had didactics for MS3/4. Seventy-seven percent of departments had a neurosurgery interest group, which was the most common method used to integrate medical students into the department. Other forms of outreach included formal mentorshipprograms (53%), lecture series (57%), and neurosurgery anatomy labs (40%). Seventy-three percent of programs provided research opportunities to medical students, and 57% indicated that the schools had a formal research requirement. On average, 3 medical students did a rotation in each neurosurgery department and 1 matched into neurosurgery each year. However, there was substantial variability among programs. Over the 2010-2016 period, the responding institutions matched as many as 4% of the graduating class into neurosurgery per year, whereas others matched 0%-1%. Departments that matched a greater (≥ 1% per year) number of medical students into neurosurgery were significantly more likely to have a neurosurgery interest group and formal research requirements. A greater percentage of high-matching programs had neurosurgery mentorship programs, lecture series, and cadaver training opportunities compared to the other institutions.

In recent decades, the number of applicants to neurosurgery has decreased. A major deterrent may be the delayed exposure of medical students to neurosurgery. Institutions with early preclinical exposure, active neurosurgery interest groups, research opportunities, and strong mentorship recruit and match more students into neurosurgery. Implementing such initiatives on a national level may increase the number of highly qualified medical students pursuing neurosurgery 3).


A medical student training camp was created to improve the preparation of medical students for the involvement in neurological surgery activities and sub-internships.

A 1-day course was held at Weill Cornell Medicine, which consisted of a series of morning lectures, an interactive resident lunch panel, and afternoon hands-on laboratory sessions. Students completed self-assessment questionnaires regarding their confidence in several areas of clinical neurosurgery before the start of the course and again at its end.

A significant increase in self-assessed confidence was observed in all skill areas surveyed. Overall, rising fourth year students who were starting sub-internships in the subsequent weeks reported a substantial increase in their preparedness for the elective rotations in neurosurgery.

The preparation of medical students for clinical neurosurgery can be improved. Single-day courses such as the described training camp are an effective method for improving knowledge and skill gaps in medical students entering neurosurgical careers. Initiatives should be developed, in addition to this annual program, to increase the clinical and research skills throughout medical student education 4).

Canada

Medical students in Canada must make career choices by their final year of medical school. Selection of students for a career in neurosurgery has traditionally been based on marks, reference letters and personal interviews. Studies have shown that marks alone are not accurate predictors of success in medical practice; personal skills and attributes which can best be assessed by reference letters and interviews may be more important. A study was an attempt to assess the importance of, and ability to teach, personal skills and attitudes necessary for successful completion of a neurosurgical training program.

questionnaire was sent to 185 active members of the Canadian Neurosurgical Society, asking them to give a numerical rating of the importance of 22 personal skills and attributes, and their ability to teach those skills and attributes. They were asked to list any additional skills or attributes considered important, and rate their ability to teach them.

Sixty-six (36%) questionnaires were returned. Honesty, motivation, willingness to learn, ability to problem solve, and ability to handle stress were the five most important characteristics identified. Neurosurgeons thought they could teach problem solving, willingness to consult informed sources, critical thinking, manual dexterity, and communication skills, but honesty, motivation, willingness to learn and ability to handle stress were difficult or impossible to teach.

Honestymotivationwillingness to learnproblem solving and Stress management are important for success in a neurosurgical career. This information should be transmitted to medical students at “Career Day” venues. Structuring letters of reference and interviews to assess personal skills and attributes will be important, as those that can’t be taught should be present before the start of training 5).

References

1)

Larkin MB, Graves E, Rees R, Mears D. A Multimedia Dissection Module for Scalp, Meninges, and Dural Partitions. MedEdPORTAL. 2018 Mar 22;14:10695. doi: 10.15766/mep_2374-8265.10695. PubMed PMID: 30800895; PubMed Central PMCID: PMC6342347.
2) , 4)

Radwanski RE, Winston G, Younus I, ElJalby M, Yuan M, Oh Y, Gucer SB, Hoffman CE, Stieg PE, Greenfield JP, Pannullo SC. Neurosurgery Training Camp for Sub-Internship Preparation: Lessons From the Inaugural Course. World Neurosurg. 2019 Apr 1. pii: S1878-8750(19)30926-X. doi: 10.1016/j.wneu.2019.03.246. [Epub ahead of print] PubMed PMID: 30947014.
3)

Lubelski D, Xiao R, Mukherjee D, Ashley WW, Witham T, Brem H, Huang J, Wolfe SQ. Improving medical student recruitment to neurosurgery. J Neurosurg. 2019 Aug 9:1-7. doi: 10.3171/2019.5.JNS1987. [Epub ahead of print] PubMed PMID: 31398709.
5)

Myles ST, McAleer S. Selection of neurosurgical trainees. Can J Neurol Sci. 2003 Feb;30(1):26-30. PubMed PMID: 12619780.

Central sulcus

Central sulcus

see also Central sulcus region

The central sulcus is a fold in the cerebral cortex in the brains of vertebrates. Also called the central fissure, it was originally called the fissure of Rolando or the Rolandic fissure, after Luigi Rolando. It is sometimes confused with the medial longitudinal fissure.

The central sulcus is a prominent landmark of the brain, separating the parietal lobe from the frontal lobe and the primary motor cortex from the primary somatosensory cortex.

The central sulcus joins the Sylvian fissure in only 2 % of cases.

During neurosurgical procedures, it is sometimes difficult to understand the cortical anatomy of this region.

In 68/82 hemispheres, the central sulcus did not reach the posterior ramus of the lateral sulcus. A knob on the second curve of the precentral gyrus was reliably identified in only 64/82 hemispheres 1).


Computed tomography scans of 71 adult patients with no pathological imaging were analyzed. The position of the bregma and the central sulcus was determined. The distances from bregma to the pre-central and post-central sulci were calculated. The relationships from the nasion and glabella to cortical structures were also assessed.

The mean distances between the bregma and the pre-central, central and post-central sulci were 26.8 ± 7.2; 47.8 ± 5.9 and 60.6 ± 5.7 mm, respectively, without gender discrepancy. The mean distance nasion-bregma and the nasion-related measures showed significant differences among sexes.

The central sulcus was located accurately, on average 47.8 mm behind the bregma, which should be used instead of nasion in order to avoid gender discrepancy. The data obtained provide useful and reliable information to guide neurosurgical procedures 2).

Central sulcus on axial imaging

Identification of the central sulcus is important to localize the motor strip (contained in the precentral gyrus). The central sulcus (CS) is visible on 93% of CTs and 100% of MRIs 3).

It curves posteriorly as it approaches the interhemispheric fissure (IHF), and often terminates in the paracentral lobule, just anterior to the pars marginalis (pM) within the pars bracket 4) (i.e. the CS often does not reach the midline).

Inferolateral portion

The inferolateral portion is difficult to identify if unable to trace the sulcus superoinferiorly. Su et al. observed that the cortex abutting the central sulcus appears isointense to the adjacent white matter on DWI, they named this the ‘invisible cortex sign’ and a study evaluated whether it could be used to identify the inferolateral central sulcus.

This observational study of 108 consecutive ‘normal’ MRI studies was performed from May 2016 to January 2017. A single axial DWI image – obtained in the anterior commissureposterior commissure plane – was selected from each scan just above the subcentral gyrus such that it included the most inferolateral portion of the central sulcus. These single images were given to 10 readers (neuroradiologists, a neuroradiology fellow and radiology trainees) who marked the central sulcus based on the presence of the ‘invisible cortex sign’. Their accuracy in identifying the central sulcus was compared with that of the principal investigators, who used tri-planar T1 volumetric MRI sequences.

One hundred and eight consecutive patients (55 female, 53 male) were selected, ranging from 18 to 81 years old (mean = 40.5, σ = 18.2). The central sulcus was correctly identified in 95.5% of cases (σ = 3.7%; range 89.4-99.1%).

The ‘invisible cortex sign’ is a highly accurate method of identifying the inferolateral central sulcus on a single axial DWI slice without relying on the more superior aspects of the sulcus 5)

Pathology

Focal cortical dysplasias (FCDs) are mainly located in the frontal region, with a particular tropism for the central sulcus.

References

1)

Rodrigues T, Rodrigues M, Paz D, Costa MD, Santos B, Braga V, Paiva Neto Md, Centeno R, Cavalheiro S, Chaddad-Neto F. Is the omega sign a reliable landmark for the neurosurgical team? An anatomical study about the central sulcus region. Arq Neuropsiquiatr. 2015 Nov;73(11):934-8. doi: 10.1590/0004-282×20150160. PubMed PMID: 26517217.
2)

Oberman DZ, Rasmussen J, Toscano M, Goldschmidt E, Ajler P. Computed Tomographic Localization of the Central Sulcus: A Morphometric Study in Adult Patients. Turk Neurosurg. 2018;28(6):877-881. doi: 10.5137/1019-5149.JTN.21145-17.1. PubMed PMID: 29165746.
3) , 4)

Naidich TP, Brightbill TC. The pars marginalis, I: A “bracket” sign for the central sulcus in axial plane CT and MRI. Int J Neuroradiol. 1996; 2:3–19
5)

Su S, Yang N, Gaillard F. Invisible cortex sign: A highly accurate feature to localize the inferolateral central sulcus. J Med Imaging Radiat Oncol. 2019 Aug;63(4):439-445. doi: 10.1111/1754-9485.12875. Epub 2019 Mar 15. PubMed PMID: 30874376.
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