A~-~
. NTduro&lrurglca
Acta Neurochir (Wien) (1991) 111:147-153
.
9 Springer-Verlag 1991 Printed in Austria
Retrosigmoidal Approach to the Posterior Cranial Fossa. An Anatomical Study J. Lang jr. and A. Samii Department of Anatomy of the University of Wfirzburg, FederaI Republic of Germany
Summary
p l a c i n g the initial b u r r h o l e . Beside the a b o v e m e n t i o n e d
An anatomical study was performed in order to obtain help for orientation regarding the retrosigmoid approach and its osteoclastic craniotomy. The insertions of the sternocleidomastoid, the splenius capitis, the longissimus capitis and the obliquus capitis superior muscles were measured. The relationships of the insertions to different landmarks were also ascertained (FHP, suprameatal spine). In 37 specimens 6 burrholes with a standardized relationship to the Frankfurt Horizontal Plane (FHP) and the external auditory meatus, were performed. Due to the results of the relationship between burrholes and the sigmoid and transverse sinuses it is possible to give an optimal position for the initial burrhole of the osteoclastic craniotomy. A burrhole performed according to the result of this study has a relatively small risk concerning iatrogenic bleeding from the sigmoid and transverse sinuses caused by the burrhead of the drill.
p r o b l e m s r e s u l t i n g f r o m l a c k o f initial o r i e n t a t i o n t h e r e
Keywords: Retrosigmoidal approach; skull-thickness; sigmoid sinus; transverse sinus; neckmuscle-insertions; burrholes; mastoid emissary. Introduction Refined
microneurosurgical
techniques
require
from the surgeon detailed anatomical knowledge. The s u r g e o n m u s t be f a m i l i a r n o t o n l y w i t h t h e d e e p ana t o m i c a l r e l a t i o n s h i p s b u t also be a b l e to o r i e n t a t e h i m s e l f by s u p e r f i c i a l l y l o c a t e d l a n d m a r k s . T h e p r e s e n t s t u d y is to be c o n s i d e r e d as d e t a i l e d aid for orientation regarding osteoclastic craniotomies for t h e r e t r o s i g m o i d a p p r o a c h a n d as a n a n a t o m i c a l res e a r c h oJ: the s u p e r f i c i a l l y l o c a t e d s t r u c t u r e s o f this region. T h e s u r g e o n w a n t s to p l a c e the initial b u r r h o l e in p r o x i m i t y to the s i g m o i d a n d t r a n s v e r s e sinus. T h i s will e n a b l e h i m to l i m i t the size o f t h e c r a n i o t o m y a v o i d i n g u n n e c e s s a r y large e x p o s u r e s , a n d also p e r m i t a n e a r l y orientation. O u r r e t r o s p e c t i v e b i b l i o g r a p h i c a l r e v i e w has d e m onstrated a lack of reliable anatomical landmarks for
is the risk o f d a m a g i n g t h e sinuses. T h e a v a i l a b i l i t y o f r e l i a b l e l a n d m a r k s w o u l d t h e r e f o r e g u i d e the s u r g e o n
and r e d u c e the risk o f i a t r o g e n i c lesions.
Material and Methods The study was performed on 37 head-halves including the upper thoracic aperture fixed by perfusing with a mixture of formaldehyde, water, Karlsbader salt, chloralhydrate, lysoformin. In our material there were 16 female and 21 male specimens. The distribution of right and left halves was equal. For the dissection of the muscles we used standard anatomical and surgical instruments. We did the measurements by mm-graphs and dividers. The burrholes were performed using a drill with a 3 mm burrhead. In order to mark the positioning of the burrholes we produced a plexiglass 6-hole template distributed in two rows of 3 holes parallel to each other and 7 mm apart. The upper row was projected on the Frankfurter Horizontal Plane (FHP) so that the foremost hole was situated 30mm behind the posterior border of the external auditory meatus. For the depth measurement of the burrholes we used special rulers adequate for our measurements. The observation and measurement of the mastoid emissary foramen and its vessels was performed with the aid of a stereomicroscope having a micrometer eyepiece. After the initial skin preparation we exposed the spina suprameatica and the external auditory meatus. The next step was the exposure and measurement of the insertion of the following muscles: m. sternocleidomastoid, m. splenius eapitis, m. Iongissimus capitis and m. obliquus capitis superior. As part of the general anatomical study of this area we also evaluated the point of entry of the uppermost branch of the accessory nerve in the sternocleidomastoid muscle in relation to other different anatomical points and landmarks (apex of the mastoid process, foremost part of the insertion of the sternocleidomastoid muscle and suprameatal spine). After the removal of the musculature from their attachements we looked for the mastoid emissary foramen in order to measure the foramen and its vessels. We proceeded by projecting on the cranium- following the above mentioned scheme - the FHP for the placement of the burrholes. The drilling was done perpendicularly to the cranial surface. In
148
J. Lang and A. Samii: Retrosigmoidal Approach to the Posterior Cranial Fossa
order to inspect the relationship between the burrholes and the sigmoid and transverse sinus we performed a fenestration of the skull with an oscillating saw and documented graphically the relationship of the burrholes to the sinuses using as control a drawing of this region.
Results
In our material the length of the insertion of the sternocleidomastoid muscle was 53 (32-70)mm (Fig. 1). The most posterior part of the insertion was 11 (0.356) mm below the FHP. From the lateral aspect the insertion of the muscle was mostly arched. The apex
3,1. (.6 to.+9,5) \[
FHP\
11,4 (0~,3-56,0)-- -
"-,,,.
I
~
41,7 (23-64) i 13,6 (0,3-28,0) ~
)
/
M. s t e r n o c l e i d o m ~
FHP\
10,6 (-6,0 to +49,0) 8,5'~(-1,0 to +16,0) [ .... \ l 35?4 (21,0-64,0)
\
(10,0-41,0)
M. splenius capitis
14,1 (5,0-28,0) 17,6 (1,0-37,0) 31,2 (29,0-34,0) FHP \
'
~
~
(11,0-44,0)
9
M. longissimus capiti s 23,01 ( 11,0-36,0 )
25,8 (8,0-69,0) I FHP 1
14,2 (10,0-20,0) l [,2,0,8 (7,0-41,0) , (22,0-51,0)
M. obliquus capitis sup. " - - - ~ -
(12,0-42,0) mm (extremals)
Fig. 1. Measurements of the sternocleidomastoid, splenius capitis, longissimus capitis, obliquus capitis superior muscles: length values, distances to the Frankfurt horizontal plane and to the suprameatal spine
of the insertion was located 42 (23-64) mm behind the suprameatal spine and 3. ( - 6 . 0 to + 9.5) mm below the FHP. The minus cipher means that this point was located above the plane. The most anterior part was 14 (0.3-28) mm under the FHP. The sternocleidomastoid muscle is innervated by the accessory cervical plexus (Fig. 2). The most cranial branch of the accessory nerve entered the muscle 47 (27-69) mm below the apex of the mastoid process. The distance between the point of entry of the nerve and the most anterior part of the insertion of the sternocleidomastoid muscle was 60 (39 80) mm and between the point of entry and the suprameatal spine 73 (44-93) mm. The length of the insertion of the splenius capitis muscle was 53 (34-73) mm (see Fig. 1). The insertion of the muscle was mostly arched with the convexity upwards. The distance from the most anterior part of the insertion to the F H P was 24 ( 1 0 4 1 ) mm. The most posterior part was 11 ( - 6 to + 49) mm below the FHP. The apex of the insertion was 9 ( - 1 to + 16) mm from the F H P and 35 (21 64) mm from the suprameatal spine. The length of the insertion of the longissimus capitis muscle was 23 (11-36) mm (see Fig. 1). The insertion of the muscle was mostly arched with the convexity upwards. The distance from the most anterior of the insertion to the F H P was 28 (11-44) mm. The most posterior part was 18 (1-37) mm below the FHP. The vertex of the insertion was 14 (5-28) mm from the F H P and 31 (29-34) mm from the suprameatal spine. The length of the insertion of the obliquus capitis superior muscle was 23 (1~42) mm (see Fig. 1). The distance of the most anterior part of the insertion to the F H P was 21 (7-41) mm and the distance to the suprameatal spine was 41 (22-51) mm. The most posterior part of the insertion was 26 (8-69) mm below the FHP. The vertex of the insertion was 14 (10-20) mm below the F H P and was 42 (32-51) mm away from the suprameatal spine. The most anterior part of the insertion was 38 (32-57) mm and the most posterior part was 55 (14-72) mm away from the apex of the mastoid process. The thickness of the skull in this area was evaluated by measuring the depth of the burrholes (Fig. 3). The relationship of the burrholes to the sinuses is illustrated by showing for each of the six differently located burrholes the percentage of the ones which would not have hit the sinuses (Fig. 4). In our material the mastoid emissary foramen existed in 78% with an average width (measured at the
J. Lang and A. Samii: Retrosigmoidal Approach to the Posterior Cranial Fossa
149
Foveola (Spina) suprameatica
kk
,,
...
-
t ~.:7::~" ~. ~
t
. NTduro&lrurglca
Acta Neurochir (Wien) (1991) 111:147-153
.
9 Springer-Verlag 1991 Printed in Austria
Retrosigmoidal Approach to the Posterior Cranial Fossa. An Anatomical Study J. Lang jr. and A. Samii Department of Anatomy of the University of Wfirzburg, FederaI Republic of Germany
Summary
p l a c i n g the initial b u r r h o l e . Beside the a b o v e m e n t i o n e d
An anatomical study was performed in order to obtain help for orientation regarding the retrosigmoid approach and its osteoclastic craniotomy. The insertions of the sternocleidomastoid, the splenius capitis, the longissimus capitis and the obliquus capitis superior muscles were measured. The relationships of the insertions to different landmarks were also ascertained (FHP, suprameatal spine). In 37 specimens 6 burrholes with a standardized relationship to the Frankfurt Horizontal Plane (FHP) and the external auditory meatus, were performed. Due to the results of the relationship between burrholes and the sigmoid and transverse sinuses it is possible to give an optimal position for the initial burrhole of the osteoclastic craniotomy. A burrhole performed according to the result of this study has a relatively small risk concerning iatrogenic bleeding from the sigmoid and transverse sinuses caused by the burrhead of the drill.
p r o b l e m s r e s u l t i n g f r o m l a c k o f initial o r i e n t a t i o n t h e r e
Keywords: Retrosigmoidal approach; skull-thickness; sigmoid sinus; transverse sinus; neckmuscle-insertions; burrholes; mastoid emissary. Introduction Refined
microneurosurgical
techniques
require
from the surgeon detailed anatomical knowledge. The s u r g e o n m u s t be f a m i l i a r n o t o n l y w i t h t h e d e e p ana t o m i c a l r e l a t i o n s h i p s b u t also be a b l e to o r i e n t a t e h i m s e l f by s u p e r f i c i a l l y l o c a t e d l a n d m a r k s . T h e p r e s e n t s t u d y is to be c o n s i d e r e d as d e t a i l e d aid for orientation regarding osteoclastic craniotomies for t h e r e t r o s i g m o i d a p p r o a c h a n d as a n a n a t o m i c a l res e a r c h oJ: the s u p e r f i c i a l l y l o c a t e d s t r u c t u r e s o f this region. T h e s u r g e o n w a n t s to p l a c e the initial b u r r h o l e in p r o x i m i t y to the s i g m o i d a n d t r a n s v e r s e sinus. T h i s will e n a b l e h i m to l i m i t the size o f t h e c r a n i o t o m y a v o i d i n g u n n e c e s s a r y large e x p o s u r e s , a n d also p e r m i t a n e a r l y orientation. O u r r e t r o s p e c t i v e b i b l i o g r a p h i c a l r e v i e w has d e m onstrated a lack of reliable anatomical landmarks for
is the risk o f d a m a g i n g t h e sinuses. T h e a v a i l a b i l i t y o f r e l i a b l e l a n d m a r k s w o u l d t h e r e f o r e g u i d e the s u r g e o n
and r e d u c e the risk o f i a t r o g e n i c lesions.
Material and Methods The study was performed on 37 head-halves including the upper thoracic aperture fixed by perfusing with a mixture of formaldehyde, water, Karlsbader salt, chloralhydrate, lysoformin. In our material there were 16 female and 21 male specimens. The distribution of right and left halves was equal. For the dissection of the muscles we used standard anatomical and surgical instruments. We did the measurements by mm-graphs and dividers. The burrholes were performed using a drill with a 3 mm burrhead. In order to mark the positioning of the burrholes we produced a plexiglass 6-hole template distributed in two rows of 3 holes parallel to each other and 7 mm apart. The upper row was projected on the Frankfurter Horizontal Plane (FHP) so that the foremost hole was situated 30mm behind the posterior border of the external auditory meatus. For the depth measurement of the burrholes we used special rulers adequate for our measurements. The observation and measurement of the mastoid emissary foramen and its vessels was performed with the aid of a stereomicroscope having a micrometer eyepiece. After the initial skin preparation we exposed the spina suprameatica and the external auditory meatus. The next step was the exposure and measurement of the insertion of the following muscles: m. sternocleidomastoid, m. splenius eapitis, m. Iongissimus capitis and m. obliquus capitis superior. As part of the general anatomical study of this area we also evaluated the point of entry of the uppermost branch of the accessory nerve in the sternocleidomastoid muscle in relation to other different anatomical points and landmarks (apex of the mastoid process, foremost part of the insertion of the sternocleidomastoid muscle and suprameatal spine). After the removal of the musculature from their attachements we looked for the mastoid emissary foramen in order to measure the foramen and its vessels. We proceeded by projecting on the cranium- following the above mentioned scheme - the FHP for the placement of the burrholes. The drilling was done perpendicularly to the cranial surface. In
148
J. Lang and A. Samii: Retrosigmoidal Approach to the Posterior Cranial Fossa
order to inspect the relationship between the burrholes and the sigmoid and transverse sinus we performed a fenestration of the skull with an oscillating saw and documented graphically the relationship of the burrholes to the sinuses using as control a drawing of this region.
Results
In our material the length of the insertion of the sternocleidomastoid muscle was 53 (32-70)mm (Fig. 1). The most posterior part of the insertion was 11 (0.356) mm below the FHP. From the lateral aspect the insertion of the muscle was mostly arched. The apex
3,1. (.6 to.+9,5) \[
FHP\
11,4 (0~,3-56,0)-- -
"-,,,.
I
~
41,7 (23-64) i 13,6 (0,3-28,0) ~
)
/
M. s t e r n o c l e i d o m ~
FHP\
10,6 (-6,0 to +49,0) 8,5'~(-1,0 to +16,0) [ .... \ l 35?4 (21,0-64,0)
\
(10,0-41,0)
M. splenius capitis
14,1 (5,0-28,0) 17,6 (1,0-37,0) 31,2 (29,0-34,0) FHP \
'
~
~
(11,0-44,0)
9
M. longissimus capiti s 23,01 ( 11,0-36,0 )
25,8 (8,0-69,0) I FHP 1
14,2 (10,0-20,0) l [,2,0,8 (7,0-41,0) , (22,0-51,0)
M. obliquus capitis sup. " - - - ~ -
(12,0-42,0) mm (extremals)
Fig. 1. Measurements of the sternocleidomastoid, splenius capitis, longissimus capitis, obliquus capitis superior muscles: length values, distances to the Frankfurt horizontal plane and to the suprameatal spine
of the insertion was located 42 (23-64) mm behind the suprameatal spine and 3. ( - 6 . 0 to + 9.5) mm below the FHP. The minus cipher means that this point was located above the plane. The most anterior part was 14 (0.3-28) mm under the FHP. The sternocleidomastoid muscle is innervated by the accessory cervical plexus (Fig. 2). The most cranial branch of the accessory nerve entered the muscle 47 (27-69) mm below the apex of the mastoid process. The distance between the point of entry of the nerve and the most anterior part of the insertion of the sternocleidomastoid muscle was 60 (39 80) mm and between the point of entry and the suprameatal spine 73 (44-93) mm. The length of the insertion of the splenius capitis muscle was 53 (34-73) mm (see Fig. 1). The insertion of the muscle was mostly arched with the convexity upwards. The distance from the most anterior part of the insertion to the F H P was 24 ( 1 0 4 1 ) mm. The most posterior part was 11 ( - 6 to + 49) mm below the FHP. The apex of the insertion was 9 ( - 1 to + 16) mm from the F H P and 35 (21 64) mm from the suprameatal spine. The length of the insertion of the longissimus capitis muscle was 23 (11-36) mm (see Fig. 1). The insertion of the muscle was mostly arched with the convexity upwards. The distance from the most anterior of the insertion to the F H P was 28 (11-44) mm. The most posterior part was 18 (1-37) mm below the FHP. The vertex of the insertion was 14 (5-28) mm from the F H P and 31 (29-34) mm from the suprameatal spine. The length of the insertion of the obliquus capitis superior muscle was 23 (1~42) mm (see Fig. 1). The distance of the most anterior part of the insertion to the F H P was 21 (7-41) mm and the distance to the suprameatal spine was 41 (22-51) mm. The most posterior part of the insertion was 26 (8-69) mm below the FHP. The vertex of the insertion was 14 (10-20) mm below the F H P and was 42 (32-51) mm away from the suprameatal spine. The most anterior part of the insertion was 38 (32-57) mm and the most posterior part was 55 (14-72) mm away from the apex of the mastoid process. The thickness of the skull in this area was evaluated by measuring the depth of the burrholes (Fig. 3). The relationship of the burrholes to the sinuses is illustrated by showing for each of the six differently located burrholes the percentage of the ones which would not have hit the sinuses (Fig. 4). In our material the mastoid emissary foramen existed in 78% with an average width (measured at the
J. Lang and A. Samii: Retrosigmoidal Approach to the Posterior Cranial Fossa
149
Foveola (Spina) suprameatica
kk
,,
...
-
t ~.:7::~" ~. ~
t
