Neurosurg Focus 19 (2):E1, 2005 Suboccipital burr holes and craniectomies GUILHERME C. RIBAS, M.D., ALBERT L. RHOTON JR., M.D., OSWALDO R. CRUZ, M.D., AND DAVID PEACE, M.S. Department of Neurosurgery, University of Florida, Gainesville, Florida; and Departments of Neurosurgery and Surgery (Clinical Anatomy Discipline), University of São Paulo Medical School, São Paulo, Brazil Object. The goal of this study was to delimit the external cranial projection of the transverse and sigmoid sinuses, and to establish initial strategic systematized burr hole sites for lateral infratentorial suboccipital approaches based on external cranial landmarks particularly related to the lambdoid, occipitomastoid, and parietomastoid sutures. Methods. The external cranial projection of the transverse and sigmoid sinuses was studied through their external outlining obtained with the aid of multiple small perforations made from inside to outside along the inner margins of the sinuses of 50 paired temporoparietooccipital regions in 25 dried adult human skulls. The burr hole placement was studied by evaluating the supratentorial, over-the-sinuses, and infratentorial components of 1-cm-diameter openings made at strategic sites identified in the initial part of the study, which was performed in another 50 paired tem- poroparietooccipital regions. The asterion and the midpoint of the inion–asterion line were found to be particularly related to the inferior half of the transverse sinus; the transverse and sigmoid sinuses’ transition occurs 1 cm anteriorly to the asterion across the parietomastoid suture, and the most superior part of the sigmoid sinus is located anteriorly to the occipitomastoid suture, with its posterior margin crossing this suture posteriorly to the most superior aspect of the mastoid process, which is located at the most superior level of the mastoid notch. Burr holes made at the midpoint of the inion–asteri- on line, at the asterion, 1 cm anterior to the asterion, just inferiorly to the parietomastoid suture, and over the occipito- mastoid suture at the most superior level of the mastoid notch are appropriate to expose the inferior half of the trans- verse sinus at its midpoint, the inferior half of the transverse sinus at its most lateral aspect, the transverse and sigmoid sinuses’ transition, and the posterior margin of the basal aspect of the sigmoid sinus, respectively. Conclusions. These findings allow an estimation of the transverse and sigmoid sinuses’ external cranial projection. The asterion and the most posterior part of the parietomastoid suture constitute a suitable initial burr hole site at which to perform an upper or asterional suboccipital craniectomy to expose the superior aspect of the cerebellopontine angle (CPA). The occipitomastoid suture at the most superior aspect of the mastoid notch constitutes an adequate initial burr hole site at which to perform a basal suboccipital craniectomy to expose the lower portion of the CPA. The sites can be used together as initial burr hole sites to perform wide suboccipital exposures, because they already constitute nat- ural infratentorial lateral limits. KEY WORDS • cranial suture • transverse sinus • sigmoid sinus • burr hole • craniotomy • suboccipital approach • cerebellopontine angle • posterior fossa Whereas the frontotemporal approaches are relatively graphic profiles of strategic burr hole sites related to these systematized in the sense that the craniotomies proceed sutures (Fig. 1). from defined burr hole sites,76,78 the lateral suboccipital ap- proaches are performed from various and nonstandardized initial burr hole placements. Because the transverse and MATERIALS AND METHODS sigmoid sinuses are the natural limits of these exposures, This study was conducted in two stages, in each of which 50 the knowledge of their cranial topography constitutes the paired temporoparietooccipital regions in 25 adult human dried main factor in the planning of these posterior approaches. skulls were studied through observations and measurements.57 In the first part, the anatomical relationships of the lambdoid, The lambdoid, occipitomastoid, and parietomastoid su- occipitomastoid, and parietomastoid sutures to the transverse and tures are easily recognizable structures on the external cran- sigmoid sinuses were studied in 25 adult human uncataloged skulls, ial surface.35,42,47,49,60–63,69–72 For this reason we initially inves- originally from India, at the Theodore Gildred Microsurgical Edu- tigated their relationships with the transverse and sigmoid cation Center of the Department of Neurological Surgery of the Un- sinuses, and based on these findings, we evaluated the topo- iversity of Florida. The calvariae of the skulls were removed above the lambda and the superior orbital ridges, the transverse and sig- Abbreviation used in this paper: CPA = cerebellopontine angle. moid sinuses superior and inferior margins were drawn on the outer Neurosurg. Focus / Volume 19 / August, 2005 1 Unauthenticated | Downloaded 09/26/21 12:36 PM UTC G. C. Ribas, et al. Fig. 1. Photographs of dried adult human skulls showing the external cranial surface (left) and the internal cranial surface (right). surface of the skulls after multiple small perforations were made on (Fig. 2). The analysis of its distance to the superior and its bone landmarks from inside to outside, and the main points to be inferior margins of the transverse sinus, and of the sinus studied were identified. height at this point, led us to conclude that the asterion is The second part of the study was done at the Anatomical Museum of the Biomedical Sciences Institute of the University of São Paulo particularly related to the inferior half of the transverse through observations and measurements obtained in 25 adult human sinus. The topography of the transverse sinus segment pos- skulls cataloged according to their race, sex, and age (Table 1).The terior to the lambdoid and occipitomastoid sutures was calvariae had already been removed in these skulls, and the points to evaluated through the disposition of the inion–asterion line be studied were lightly marked with a pencil. in relation to the sinus (Fig. 3). The burr hole study was conducted by evaluation of the posteri- The analysis of the distances to both margins from the or fossa, the area over the sinuses, and supratentorial components of midpoint of the inion–asterion line, and the sinus height at 1-cm-diameter burr holes placed at strategic sites related to the cran- ial sutures. The burr holes were plotted with the aid of a circular de- that point, showed that its position in relation to the trans- vice adapted to a compass, and the measurements of the height of verse sinus is similar to the disposition of the asterion, each burr hole’s topographic components provided the data to elab- being also related to the inferior aspect of the sinus sulcus orate its topographic profile. (Fig. 4). An extensive statistical analysis was done to compare the results The topography of the part of the transverse sinus ante- among the different sides, sexes, and races. RESULTS Anatomical Relationships of the Lambdoid, Occipitomastoid, and Parietomastoid Sutures With the Transverse and Sigmoid Sinuses Anatomical Relationships of the Lambdoid and Occipitomas- toid Sutures With the Transverse Sinus. The relationships of the lambdoid and occipitomastoid sutures with the trans- verse sinus were evaluated through the asterion position Fig. 2. Schematic drawing showing the variation of the asteri- on’s position in relation to the transverse sinus (mean values, tak- ing into account variations between races). Values in all schematic TABLE 1 drawings except Fig. 3 are given in centimeters, and commas Identification of the 25 catalogued skulls studied denote decimal points. Feature Value race African-American 7 Caucasian 9 mixed 9 sex F11 M 14 age (yrs) min 18.0 max 60.0 mean 33.9 Fig. 3. Schematic drawing showing the disposition of the median 34.0 inion–asterion line in relation to the transverse sinus. 2 Neurosurg. Focus / Volume 19 / August, 2005 Unauthenticated | Downloaded 09/26/21 12:36 PM UTC Suboccipital burr holes and craniectomies Fig. 4. Schematic drawing showing variation in the position of Fig. 8. Schematic drawing showing variations in the position of the midpoint of the inion–asterion line in relation to the transverse the occipitomastoid suture/sigmoid sinus posterior margin crossing sinus (mean values, taking into account variations between races). point along the occipitomastoid suture (mean values, taking into account variations between races). rior to the lambdoid and occipitomastoid sutures was eval- uated through analysis of the disposition of its most antero- superior and anteroinferior points in relation to the asteri- on. These points, which were equivalents to the superior and inferior aspects, respectively, of the transverse sinus/ sigmoid sinus transition, presented the disposition depicted in Fig. 5 in relation to the asterion. Anatomical Relationships of the Parietomastoid Suture With the Transverse Sinus. These relationships were initial- ly evaluated through analysis of the transverse sinus’ most anterosuperior and its most anteroinferior points in relation to this suture. Whereas the position of the point corre- sponding to the superior aspect of the sinuses’ transition varied from 0.1 to 0.3 cm above the parietomastoid suture, the point corresponding to the inferior aspect of the sinus- Fig. 5. Schematic drawing showing the disposition of the most es’ transition was