Surgical anatomy of sigmoid sinus with evaluation of its venous dominance for advances in preoperative planning

A new anatomical finding: the paramastoid diverticulum of the sigmoid sinus

PURPOSE

The sigmoid sinus (SS) is a major surgical landmark. The paramastoid process (PMP) occurs rarely. Inferior diverticula of the SS were not found or reported previously. We aimed to determine the incidence and detailed anatomy of such morphology of the SS.

METHODS

Archived angioCT files of 25 males and 25 females were used. The morphology of the SS was checked on planar sections and by three-dimensional volume renderings.

RESULTS

In 3 female cases (6%), inferior paramastoid diverticula of the SS (PMDSSs) were found, two on the right and one on the left. They were all protruding on the inferior side of the jugular process of the occipital bone. Their heights and inner diameters were, respectively, 9.94/11.01 mm, 8.21/4.85 mm and 5.97/8.72 mm. A high jugular bulb was also found on that side in each case. Each PMDSS had a thin or dehiscent bottom. They were closely related to condylar veins, the occipital artery, the vertebral artery and its venous plexus.

CONCLUSION

The PMDSS should not be mistaken as a PMP to avoid surgical lesions of the SS. The PMDSS is an unexpected landmark in the suboccipital region.

Morphometric Analysis of the Retrolabyrinthine Approach to the Posterior Fossa

INTRODUCTION

The retrolabyrinthine approach provides shorter working distance and less cerebellar retraction compared with the retrosigmoid approach to the internal acoustic canal (IAC) and cerebellopontine angle cistern. However, exposure of the ventral surface of the brainstem and petroclival region may be restricted. Trautmann's triangle (TT), an area intimately related to this region, demonstrates significant anatomical variability, which may adversely affect the ease of the approach. The aim of this study is to evaluate anatomic parameters of the posterior fossa that may anticipate a challenging situation in approaching the IAC and the petroclival region through the retrolabyrinthine approach.

METHODS

It was performed a radioanatomic analysis of 75 cerebral angiotomography exams to identify parameters that could potentially reduce areas of surgical exposure.

RESULTS

Large variations were observed in the area of exposure of the TT (553%) and the height of the jugular bulb (234%). Shorter distances from the sigmoid sinus to the posterior semicircular canal and high-riding jugular bulb were associated with smaller areas of exposure. Dominant and laterally positioned sigmoid sinuses and less pneumatized mastoids were associated with potentially unfavorable conditions, including a narrower angle of attack to the IAC. Increased petrous slopes and petroclival angles were associated with smaller petroclival areas and shallower clival depths.

CONCLUSIONS

This study of the posterior fossa reveals remarkable anatomic variation in the region. These findings should be taken into consideration during the preoperative planning of retrolabyrinthine approaches in order to offer safer and more effective surgical procedures.

An anatomical study of the sigmoid sinus artery: Application to the transmastoid approach

INTRODUCTION

We aimed to investigate the morphological features of the artery that traverse the sigmoid sinus's lateral surface and to discuss this structure's clinical relevance.

METHODS

Ten sides from five cadaveric Caucasian heads were used for gross anatomical dissection to investigate the morphological features of the sigmoid sinus artery (SSA), and additional five sides were used for histological observation.

RESULTS

The SSA was found on eight out of ten sides (80%). The mean diameter of the SSA was 0.3 mm. The mean distance from the tip of the mastoid process to the artery was 20.3 mm. Histological observation identified extradural and intradural courses of SSA. The intradural course was further categorized into protruding and non-protruding types. In the protruding type, the SSA traveled within the dura but indented into the bone, making it more or less an intraosseous artery. In the non-protruding type, the SSA traveled within the dura but did not protrude into the bone but rather indented into the lumen of the SS. In all sections, both intradural and extradural courses were identified simultaneously.

CONCLUSIONS

When the mastoid foramen is observed, it does not always only carry an emissary vein but also an artery. The SSA could be considered a "warning landmark" during bone drilling for the transmastoid approach.