| Objectives:An observation study was applied in counting the number of foramina existing in human dry skulls,which included parietal foramen(PAF),mastoid foramen(MSF),internal jugular foramen(IJF)and condylar canal(CDC).And the diameters of foramina were measured for preliminarily estimating the pattern of intracranial venous blood output.While a stimulation of neck posteromedial approach operation method was adopted on cadavers via micro-dissection to explain the distribution of venous plexus in the occipitocervical region.Methods:1.290 human dry skulls were collected from three labs in three different universities,and the parietal foramen,mastoid foramen,internal jugular foramen and condylar canal of each specimen were carefully recorded;2.30 random skulls were obtained from the Anatomy Laboratory of Kunming Medical University,and the diameter of parietal foramen,mastoid foramen,internal jugular foramen and condylar canal were measured delicately via a digital vernier caliper;3.A stimulation of neck posteromedial approach operation method was carried out in the occipitocervical region of 10 cadavers through micro-dissection,and the specimen were all contributed by the Anatomy Laboratory of Kunming Medical University.Results:1.EJF is an irregular big foramen existing in the middle fossa of the skull base,which is constant as one foramen bilaterally.If regard the EJF as a quasi-oval foramen,the minor axis on the left is 5.90±1.65 mm,and on the right is 7.18±1.99 mm,p value is bigger than 0.05 which means no statistical significance and the bilateral comparison doesn't have significant difference;major axis on the left is 12.56±3.16 mm,13.39±2.08 mm on the right,p value is smaller than 0.05 which means there is statistical significance and the bilateral comparison has significant difference;2.MAF is inconstant in number.Within our observation,the average number of MAF on the left is 1.43 and 1.47 on the right side;MAF absence was discovered in 32 skulls on the left side and 20 on the right;there is 133 case which has single MAF on the left and 137 on the right;99 cases of double MAF on the left and 108 on the right;20 cases with three MAF on the left and 21 on the right;and 4 cases with four MAF on the left and two on the right,Fora.l diameter of mastoid on the left is 1.23±0.63mm,1.18±0.66mm on the right;Diameter of Fora.2 on the left is 1.58±0.61mm,1.29±0.96mm on the right;Diameter of Fora.3 on the left is 1.07±0.56 mm,on the right is 1.10±0.50 mm;Diameter of Fora.4 on the left is 0.55±0.04 mm,1.92±0.48 mm on the right;maximum of the left is 2.71mm and 4.17mm on the right with p value is bigger than 0.05 which means no statistical significance and the bilateral comparison doesn't have significant difference;3.CDC is inconstant either,and the absence rate of CDC is 138/578 which 67 cases of CDC absent occur on the left and 71 on the right,and there isn't significant difference between the left and right side(p>0.05,data is not presented).The exiting foramen diameter of CDC on the left is 2.15±0.83mm,2.73±0.91mm on the right with p value is bigger than 0.05 which means no statistical significance and the bilateral comparison doesn't have significant difference,and the maximum on the left is 3.75mm,4.04mm on the right;4.PAF has a one foramen bilaterally characteristic,some cases has the unilateral PAF and multiple-PAF were also detected.There is a rate of 115/472 which the PAF was absent,and the left side has domination comparing to the right;double PAF occurred in 15 cases and two cases has three PAF and four PAF individually.The caliber of the first parietal foramen on the left is 1.03±0.49mm;0.88±0.38mm on the right;and second on the left is 0.90±0.46mm,0.27mm on the right(Only one case with dual PAF on the right side)with p value is bigger than 0.05 which means no statistical significance and the bilateral comparison doesn't have significant difference,and the maximum on the left is 1.92mm and 1.51mm on the right;5.Based on the measurement,we can calculate that the total average area of the left is 63.5mm2±26.2mm2 and which is smaller than the right side(83mm2±33.1mm2),the diameter of the four types of foramina are as IJV(132.7mm2±7.2mm2)>CDC(6.9mm2±6.3mm2)>MSF(5.6mm2±4.2mm2)>PAF(1.2mm2±1.0mm2);6.The superficial venous plexus in OCR occurs beneath the belly of splenius capitis.It may collect the veins coming from occipital portion,mastoid process,posterior auricular vein et al,and drainage toward the deep venous plexus of OCR(Or may drainage to external jugular vein).7.The venous plexus in OCR which lay between the space of semispinal capitis and posterior atlantoaxial membrane(surrounding by the muscle group of suboccipital triangle)and which may collect the venous blood from intracranially and occipital venous plexus,which has connection with the mastoid emissary veins and occipital emissary veins;and drain to vertebral vein,posterior vertebral venous plexus,deep jugular veins,external jugular vein et al;8.The collection point of venous plexus in OCR has a distance to skull base on the left is 9.23±0.94 mm,9.47±0.93 mm on the right;to the posterior arch of atlas on the left is 11.60±1.22 mm,11.79±1.11 mm on the right;to posterior midline on the left is 27.85±1.91 mm,27.55±2.76 mm on the right;the bilateral distance comparison of collection point of venous plexus in OCR to skull base,posterior arch of atlas and posterior midline has a p value bigger than 0.05 which means no statistical significance and the bilateral comparison doesn't have significant difference;9.Ditissimus venous plexus has been discovered beneath the posterior atlantoaxial membrane which can also be called as posterior intraspinal venous plexus(PISVP).It has a tightly connection with the lateral portion of spinal dura mater,inferior of posterior atlas arch and superior of posterior axis arch;The venous plexus-rich portion occurs at superficial layer of C2,which is beneath the posterior atlantoaxial membrane and fill the space of atlantoaxial space attaching tightly to inferior of posterior atlas arch and superior of posterior axis arch;PISVP between atlas and axis can regarded as an up-side-down trapezoid which the bottom can be seemed as the inferior part of posterior atlantal arch;top be the superior portion of posterior axoid arch;and waist respectively be the transverse process of atlanto-axial space and medial portion of atlanto-axial space which the line coming from approximately 1.5cm to posteromedial on posterior atlas arch and approximately 2.0cm to posteromedial on posterior atlantal arch;Conclusions:1.Due to there is connection between the venous plexus of the occipitocervical region and mastoid emissary veins and occipital emissary,this maybe one of the reason that intraoperative bleeding occurs when operation was performed in this region;additionally,the emissary veins in the skull play some roles in the venous blood outflow from the intracranial region,and there efficacy may act as IJV>CC>MAF>PAF;2.The deeper venous plexus in OCR was displayed as two main portion:? lay between the space of semispinal capitis and posterior atlantoaxial membrane(surrounding by the muscle group of suboccipital triangle)and which may collect the venous blood from intracranially and occipital venous plexus,which has connection with the mastoid emissary veins and occipital emissary veins;and drain to vertebral vein,deep jugular veins,external jugular vein et al;? The second part lays beneath the AAM(Or can be regarded as the posterior intraspinal venous plexus.Due to there isn't important structure between 1.5cm to the dorsal central on the posterior atlantal arch and the distance can be bigger on posterior arch of axis,and this can be deemed as a safety portion when preform operation in occipitocervical region.And more careful dissection was needed when dissection to this portion,and this may decrease the intraoperative errhysis. |
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