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Relationships of the cisternal segment of the trochlear nerve

R. Shane Tubbs and W. Jerry Oakes

Object. The cisternal portion of the trochlear nerve (fourth cranial nerve) can easily be injured during intracranial surgical operations. To help minimize the chance of such injury by promoting a thorough understanding of the anatomy of this nerve and its relationships to surrounding structures, the authors present this anatomical study.

Methods. In this study, in which 12 cadaveric heads (24 sides) were used, the authors describe exact distances between the trochlear nerve and various surrounding structures. Also described are relatively safe areas in which to manipulate or enter the tentorium, and these are referenced to external landmarks.

Conclusions. This information will prove useful in planning and executing surgical procedures in and around the free edge of the tentorium cerebelli.

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Trochlear Nerve

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The apical ligament: anatomy and functional significance

R. Shane Tubbs, Paul Grabb, Alan Spooner, Wally Wilson, and W. Jerry Oakes

Object. The authors conducted a study to describe the detailed anatomy of the apical ligament and to acknowledge or refute its historical description as a functionally significant contributor to craniocervical stability.

Methods. In 20 adult human cadavers measurements of the apical ligament were obtained, and its detailed anatomy was observed. Ranges of motion were also assessed to discern the function of the apical ligament.

Conclusions. Results of the study support the concept that the apical ligament is best described as a vestigial structure that offers no significant added stability to the craniocervical junction. In fact, this ligament was absent in 20% of the specimens examined. These data will aid physicians who frequently view images or manage clinical problems of the craniocervical junction because they may focus on other ligaments of this area and not the apical ligament.

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Superficial surgical landmarks for the transverse sinus and torcular herophili

R. Shane Tubbs, George Salter, and W. Jerry Oakes

Object. The purpose of this anatomical study is to identify reliable external landmarks that can be used to determine accurately the lower border of the proximal segment of the transverse sinus (TS).

Methods. The authors used 15 formalin-fixed cadaveric specimens for this project. Various anatomical structures were dissected and measurements of the distance between these structures and the proximal TS were obtained.

The data collected in this study demonstrate that the inion is not always a reliable external landmark to use when determining the internal location of the very proximal TS and its drainage into the area of the torcular herophili. In addition, the authors found that the most accurate external landmark to use in reliably estimating the internal placement of the proximal TS is the point of insertion of the musculus semispinalis capitus and not the superior nuchal line. In the present study, this muscle never covered more than 5 mm of the inferior edge of the TS and was found to be a reliable anatomical structure for avoiding the medial segment of the TS.

Conclusions. These findings could aid the surgeon in localizing the TS with various midline approaches to the posterior fossa and the craniocervical junction.

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Spinal neurenteric cysts and their relation to more common aspects of occult spinal dysraphism

Michael J. Rauzzino, R. Shane Tubbs, Eben Alexander III, Paul A. Grabb, and W. Jerry Oakes


Neurenteric cysts are infrequently reported congenital abnormalities believed to be derived from an abnormal connection between the primitive endoderm and ectoderm. The authors report a series of 13 patients treated over a 50-year period.


Of the 13 patients, seven were female and six were male. Their ages at presentation ranged widely from 5 weeks to 52 years of age. Children presented more commonly with cutaneous stigmata of occult spinal dysraphism (OSD) whereas adults presented primarily with pain. Neurological deficit as a presenting symptom was less common in our series, a finding that reflects the slow growth of these lesions. In all but one patient some form of vertebral anomaly was associated with the cystic lesions, including two patients with Klippel–Feil abnormalities. There was a high incidence of associated forms of OSD including split cord malformation, lipoma, dermal sinus tract, and tethered spinal cord. In previous reports the authors have suggested that neurenteric cysts are more common in the cervical region and in a position ventral to the cord. In the present series these cysts most commonly occurred as intradural, extramedullary masses in the thoracolumbar region, situated dorsal to the spinal cord. The median follow-up period was 7.5 years, and postoperative outcome reflected a patient's preoperative neurological status; in no patient was outcome worsened due to surgery.


Complete excision of the neurenteric cyst remains the treatment of choice, as subtotal excision is associated with recurrence.

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The denticulate ligament: anatomy and functional significance

R. Shane Tubbs, George Salter, Paul A. Grabb, and W. Jerry Oakes

Object. The authors conducted a study to examine the detailed anatomy of the denticulate ligaments and to assess their classic role in spinal cord stability within the spinal canal.

Methods. Detailed observation of the denticulate ligaments in 12 adult cadavers was performed. Stress was applied in all major planes to discern when the ligaments would become taut, and at the same time, gross motion of the cord was observed at sites distal to the stresses applied. Tension necessary for avulsion of the ligaments in various areas of the spinal cord was also measured.

Conclusions. These results show that the denticulate ligaments do not inhibit cord motion to such discrete areas of the cord as was once thought. The authors have determined that the ligaments are stronger in the cervical region and that they decrease in strength as the spinal cord descends. These findings are demonstrative of the denticulate ligaments being more resistant to caudal compared with cephalad stresses in the cord. Anterior and posterior motion is constrained by these ligaments but to a limited degree, especially as one descends inferiorly along the cord. Further embryological and functional studies of these ligaments is needed in non—formalin fixed tissues.

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Landmarks for the Transverse Sinus and Torcular Herophili

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Sagittal suture as an external landmark for the superior sagittal sinus

R. Shane Tubbs, George Salter, Scott Elton, Paul A. Grabb, and W. Jerry Oakes

Object. Historically, the sagittal suture has been used as an external landmark to indicate the middle portion of the superior sagittal sinus (SSS). The goal of this study was to verify this relationship.

Methods. The authors examined 30 adult cadavers to reveal the location of the SSS with respect to the sagittal suture. Their findings demonstrated that the SSS is deviated to the right of the sagittal suture in the majority of observed specimens, although the maximum displacement to the right side was never more than 11 mm.

Conclusions. This information should be useful to the neurosurgeon who must be aware of the SSS and its relationship with superficial skull landmarks.

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Surgical landmarks for the proximal portion of the axillary nerve

R. Shane Tubbs, W. Jerry Oakes, Jeffrey P. Blount, Scott Elton, George Salter, and Paul A. Grabb

Object. The proximal segment of the axillary nerve (ANp) is often difficult to identify without extensive dissection deep into the axilla. The present study was performed to find reliable surgical landmarks for this nerve.

Methods. Thirty dissections of human cadavers were performed to determine the relationships between the ANp and specific anatomical structures.

The authors found that the ANp is consistently located within an anatomical triangle constructed by lines passing between the coracobrachialis and pectoralis minor muscles and the axillary artery. In addition, the ANp was routinely found 4 cm distal to the coracoid process of the scapula.

Conclusions. These findings should assist the surgeon in locating the ANp during brachial plexus reconstruction.

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Superficial surgical landmarks for the frontal sinus

R. Shane Tubbs, Scott Elton, George Salter, Jeffrey P. Blount, Paul A. Grabb, and W. Jerry Oakes

Object. There is a lack of reports in the literature that contain descriptions of superficial anatomical landmarks for the identification of the internally located frontal sinus. Neurosurgeons must often enter the cranium through the frontal bone and knowledge of the frontal sinus is essential to minimize complications.

Methods. Seventy adult cadaveric frontal sinuses were evaluated. Measurements included both the lateral and superior extent of the frontal sinus in reference to a midpupillary line, and the superior extent of the frontal sinus from the nasion. Frontal sinuses were found bilaterally in all specimens. The mean height of the frontal sinus superior to the nasion was 2.8 cm. In 71.4% and 74.3% of specimens the lateral extent of the frontal sinus was found to be medial to the left and right midpupillary line, respectively. Distances superior to a plane drawn through the supraorbital ridges at a midpupillary line included a mean of 2.5 mm for the left side and 1.8 mm for the right side.

Conclusions. Of 70 sinuses, none extended more than 5 mm lateral to a midpupillary line. At this same midpupillary line and at a plane drawn through the supraorbital ridges, the frontal sinus was never higher than 12 mm. Finally, in the midline the frontal sinus never reached more than 4 cm above the nasion. These measurements will assist surgeons who must manipulate the frontal bone.