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Monsef.
Alexandria Bulletin
509
BONY VARIATIONS IN THE CEREBRAL ASPECT OF PETROMASTOID PART
OF ADULT EGYPTIAN TEMPORAL BONES
Amal Abdel Monsef
Department of Anatomy, Faculty of Medicine, University of Alexandria
ABSTRACT
Objective: To illustrate different bony variations in the cerebral aspect of the petromastoid part of temporal bone.
These variations were either in the mastoid emissary foramina, or in unlabelled bony projections or notches
related to the superior petrosal and sigmoid sulci or sinuses. To the best of our knowledge these variations have
not been reported before in Egyptians and may be of surgical importance.
Methods: One hundred and thirty adult Egyptian temporal bones were used in this study. These bones were
obtained form 60 dried skulls and 5 cadaveric heads after removal of their calvarias, brain and dura mater. Three
dimensional (3D) reconstructed images multislice C.T. were done for ten adult patients (6 males and 4 females).
Those patients were suffering from headache, ataxia, blurring of vision or epileptic fits with no organic brain
lesions.
Results: Bony projections were observed either above or below the superior petrosal sulcus, and on the medial
margin of the notches on the upper part of the sigmoid sulcus (at the angle between the sigmoid and transverse
sinuses). The sigmoid notch was found to be formed by the sigmoid sinus indenting the petromastoid part of
temporal bone. These projections were either small bony elevations, sharp spines (pointed or bifid), multiple
projections fused at their bases to form winged spinous processes, or shelf like projections.
The bony projections were found in 60 temporal bones (46.15%). These projections were bilateral in 20 temporal
bones (33.3%), and unilateral in 40 (66.6%) either on right or left side. They were found on the left side in 35
temporal bones (58.33%) and on the right in 25 temporal bones (41.66%). So bony projections were more likely to
be on the left side than the right side. The projections were divided according to their approximate sizes into small
(62.85% on the left, and 72% on the right), medium (28.57% on the left, and 20% on the right) or large (8.57%on
the left and 8% on the right)
Radiological results confirmed the anatomical findings. Bony projections and notches were either absent or
present on both sides of the same skull. However asymmetrical Variations of these projections and notches were
also observed in the same skull.
Conclusion: Bony projections located superior or inferior to superior petrosal sulcus may act as pegs for
attachment of the tent shaped-tentorium cerebelli, while projections on the medial margin of sigmoid sulcus (as the
sigmoid sinus indented the petromastoid portion) may be formed by strong retinaculum-like band of dura mater
pulling at the bone. This retinaculum may be responsible for the angulation between the sigmoid and transverse
sinuses. These bony projections, when present, could be detected easily by multislice C.T. scan. They will be
encountered during surgical operations involving the skull-base, whenever dissection of tentorium or ligation of
sigmoid sinus is needed. Thus, awareness of its presence in close proximity to the sigmoid and superior petrosal
sinuses is of surgical importance. Hence multislice C.T is recommended preoperatively to detect these bony
projections.
Abbreviations:
• C.T.: computed tomography.
• 3D: three dimensional
The petrous part of temporal bone has a base
INTRODUCTION
Dissection of the temporal bone has continued to directed laterally, apex that forms the posterolateral
play an important role in training the boundary of foramen lacerum, three surfaces and
otolaryngologist the anatomy of the temporal bone. three margins. The anterior surface forms the floor
This normal anatomic dissection has become of middle cranial fossa and is continuous with the
increasingly important to help the otolaryngologist cerebral surface of the squamous part. The posterior
to coordinate structural knowledge through surface forms the anterior part of posterior cranial
dissection with improved computed tomography fossa and is continuous with the inner surface of the
(C.T.) of the temporal bone and to recognize mastoid portion. The inferior surface, rough and
irregular, is part of the external surface of the skull
abnormal pathology.(1)
(3)
The petromastoid part of the temporal bone is base.
The transverse sinuses begin at the internal
encountered in a variety of surgical approaches for
occipital
protuberance. Each transverse sinus passes
both neurosurgeons and otologic surgeons. Only by
laterally
and
forwards to the posterolateral part of
cadaveric dissections the surgeons know the
petrous
temporal
bone, where it curves down as
anatomical details crowded together in a narrow
space of temporal bone and their extreme variability. sigmoid sinus. It is joined by the superior petrosal
By this knowledge the otologic surgeon can safely sinus. The sigmoid sinuses are direct continuations
traverse the perilous anatomy of temporal bone so as of the transverse sinuses, beginning where the latter
to avoid injury to many vital structures concealed in leave the tentorium cerebelli. Each sigmoid sinus
curves downwards and medially in a deep groove on
this region.(2).
Bull. Alex. Fac. Med. 42 No.2, 2006.
ISSN 1110-0834
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Variations Temporal bones Egyptians.
the mastoid part of temporal bone, crosses the
jugular process of the occipital bone and then turns
forwards to become the superior bulb of the internal
jugular vein in the posterior part of the jugular
foramen. Each sinus communicates with the vein of
the pericranium by means of the mastoid and
condylar veins.(4).
Consultation of standard reference books failed to
supply an answer as to the normal variations of the
cerebral surface of petromastoid part of temporal
bone other than the petrous bone is marked by
depressions and eminences for the convolutions of
the inferior surface of the cerebral temporal lobe.(5).
This work was planned to study the cerebral
aspect of petromastoid part of temporal bone to
illustrate different variations in this part. These
variations were either in the mastoid emissary
foramen related to the sigmoid sulcus, or in
unlabelled bony projections and notches in relation
to the superior petrosal and sigmoid sulci. To the
best of our knowledge, these projections and notches
have not been reported before in Egyptians, and its
study may prove to have a surgical importance.
METHODS
This study was conducted on 130 adult Egyptian
temporal bones irrelevant to sex. These bones were
obtained from 60 dried skulls and 5 cadaveric
heads after removal of their calvarias, brain and
dura mater. The dried skulls were collected
from the dissecting room, museum of anatomy and
from belongings of medical and dental students in
faculty of medicine and faculty of dentistry
Alexandria University. Skulls showing pathological
evidences were excluded. Three dimensional (3D)
reconstructed images multislice C.T. at the level of
the superior border of petrous temporal bone were
done for ten adult patients (6 males and 4 females).
Those patients were suffering from headache, ataxia,
blurring of vision or epileptic fits, but no organic
brain lesions were found.The cerebral surface of
petromastoid part of temporal bone was examined
for the presence of bony projections or notches. Site,
side and relation of these bony projections to the
sigmoid and superior petrosal sulci were noted. The
approximate sizes of bony projections were
measured. Each projection was classified according
to its approximate size into: small ≤ 1mm, medium
from 1 to 3mm, and large > 3mm. The depth of the
sigmoid sulcus and the variations of mastoid
emissary foramen were recorded.
RESULTS
I- Results Obtained from Dried Skulls and
Cadaveric Heads:
Sixty dried skulls and 5 cadaveric heads were used
in this study to obtain 130 temporal bones.
1-Laterality and Side of Temporal Bony
Projections:
In general the bony projections were found in 60
Bull. Alex. Fac. Med. 42 No.2, 2006.
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(46.15%) out of 130 temporal bones. The bony
projections were unilateral in 40 temporal bones
(66.6%) and bilateral in 20 (33.3%). The bony
projections (uni - and bilateral) were left sided in 35
out of 60 temporal bones (58.33%), and right sided
in 25 temporal bones (41.66%) (Table I).
2-Size of Temporal Bony Projections:
As regards the left side projections, 62.85% (22
left temporal bones out of 35) were small, 28.57%
(10 left temporal bones) were medium and 8.57% (3
left temporal bones) were large in size. Seventy two
percent of the right side projections (18 right
temporal bones out of 25) were small, 20% (5 right
temporal bones) were medium and 8% (2 right
temporal bones) were large in size. The temporal
bony projections were mostly of small size (66.66%)
(Table II).
3-Anatomical Description of the Temporal Bony
Projections:
Examination of the cerebral aspect of
petromastoid part of temporal bone confirmed the
well-recognized anatomy. Petrous and mastoid parts
of the temporal bone form the lateral wall of the
posterior cranial fossa. The sigmoid sulcus grooved
the posterior aspects of the mastoid part while the
superior petrosal sinus grooved the superior border
of petrous part of temporal bone (Fig. 1). The
internal auditory meatus opened into the posterior
surface of petrous temporal bone, and the jugular
foramen was present between the occipital bone and
petrous temporal bone (Figs. 1, 2). Bony projections
of variable sizes were observed related to the
sigmoid sinus groove and superior petrosal sulcus
(Figs. 2, 3, 4).
The base of these projections blended gently with
the petrous part of temporal bone. An exact merging
point could not be determined so that they could not
be precisely measured.
4-Bony Features Related to Sigmoid Sulcus:
Examination of sigmoid sulcus revealed different
variations in depth. It was deep (Figs. 3, 4) or
shallow (Fig. 1). It passed through the posterior
aspect of mastoid part of temporal bone (Fig. 1). In
60 temporal bones (46.15%) the sigmoid sinus
indented also the superior border of petrous temporal
bone to form a notch (Fig. 2). These notches were
either deep (Figs. 4 – 8) or shallow (Figs. 2, 9).
Comparing the depth of notches in the two sides of
the same skull, these notches were of the same depth
in both sides (Figs. 5, 9), or deeper on the right side
(Fig. 10). The notch was found to be related
medially to bony projections of different size and
shape (Figs. 2 – 8). In only one skull a well marked
crest shape elevation was located lateral to this
notch. This crest was present on the upper border of
the left transverse sulcus (Fig. 9a). The bony
projections were opposite the angle between the
sigmoid and transverse sinuses (Fig. 2).
The bony projections related to the sigmoid sinus
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were single (Figs. 3, 5b, 6 - 8), double (Fig. 2) or
multiple (Figs. 4, 9b, 10). The single projection was
located between the notch and the inferior border of
superior petrosal sulcus (Figs. 5, 6), the double
projections were located above and below the
superior petrosal sulcus between it and the notch
(Fig. 2), while the multiple projections were
extending medially inferior to the superior petrosal
sulcus (Figs. 4, 9b, 10). The shape of these bony
projections were either simple elevation (Fig. 5b) or
sharp spine (pointed: Figs. 3, 6, 7, or bifid: Fig. 4).
Their approximate sizes were variable; either small
(Fig. 5a), medium (Figs. 2, 5b, 6 – 9) or large (Fig.
3). The tips of the spines were directed laterally i.e.
towards the sigmoid sulcus (Fig. 6). Some of them
were long with attempts to bridge the sigmoid sulcus
(Fig. 3).
The mastoid emissary foramen was absent (Fig.
10) or present in relation to the sigmoid sulcus (Figs.
4 – 8). It opened into the sigmoid sulcus itself
(Figs. 6b, 8), at its margin (Fig. 4) or outside the
sulcus (Fig.6a,7). The mastoid emissary foramen
illustrated different variations in size. By subjective
assessment, these foramina were small in size (Figs.
4, 6), medium (Figs. 5b, 8) or large (Fig. 7). This
foramen opened in the upper part of the sigmoid
sulcus (Figs. 6a, 7, 8) or at a lower level (Fig. 6b).
5- Bony Projections Related to the Superior
Petrosal Sulcus:
Bony projections were located superior (Fig. 8) or
inferior to the superior petrosal sulcus (Figs. 4, 9,
10). These bony projections were single (Fig. 9a) or
multiple projections fused at their bases to form
winged spinous process (Figs. 4, 10a). These
multiple projections were separated from the bony
elevation forming the medial margin of the sigmoid
notch (Fig. 10a) or fused with it (Fig. 4).
II-Results
of
the
three
Dimensional
Reconstructed Images C.T.:
In only one patient there was bilateral absence of
bony projections and notches in relation to the
superior border of petrous temporal bone (Fig. 11).
In nine patients, asymmetrical variations of the right
and left sides of the same skull were observed (Figs.
12-16).
In one patient, there were bony projections located
superior and inferior to the superior petrosal sulcus
(Fig. 12). The projections above the superior
petrosal sulcus were single, while those below the
sulcus were double and of variable shape. They were
either in the form of sharp spine with its tip directed
laterally or in the form of simple bony elevation
(Fig. 12). By subjective assessment of their sizes,
they were either small or medium (Fig. 12). Another
group of bony projections were found laterally, on
the superior border of petrous bone (in 10 temporal
bones-7 left & 3right). They were of variable shape
and size. Their shape was either simple projection
(Figs. 13, 15, 16b) or spine (Figs. 13, 14, 16a). By
subjective assessment, their sizes were small (in
8temporal bones-6left &2right, Figs. 13, 16a) or
medium (in 2temporal bones-one left &one right,
Figs. 14, 16b).
These laterally located bony projections were
either associated with the presence of sigmoid notch
lateral to it (Figs. 12, 14, 15) or were present alone
without this notch (Figs. 13, 16). These notches were
deep (Figs. 14, 15) or shallow (Figs. 12, 13).
Comparing the depth of notches in the two sides of
the same skull, they were deeper on the right (Fig.
15). The sigmoid notches were bilaterally absent (in
4patients, Fig. 16) or present (in one patient, Fig.
15). They were present on the right (unilateral) (in
one patient, Fig. 13) or on the left (in 4patients, Figs.
12, 14). In only one male patient aged 24 years a
shelf like projection was found on the right side of
the skull. This projection was located inferior to the
superior petrosal sulcus and extended laterally to
form the medial margin of the sigmoid notch (Fig.
15). Sex correlation could not be determined due to
the small number of the living cases.
Table I. Temporal bony projections according to laterality and side
No.
%
- Laterality
- Unilateral
40 66.66
- Bilateral
20 33.33
- Side
- Right
25 41.66
- Left
35 58.33
Total
60 100.00
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Variations Temporal bones Egyptians.
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Table II. Temporal bony projections according to size:
Size
Small
Medium
Large
Total
Left
No
%
22
62.82
10
28.57
3
8.57
35
100.00
Right
Total
No
%
No
%
18
72.00
40
66.66
5
20.00
15
25.00
2
8.00
5
8.33
25
100.00
60
100.00
Figure 1. A photograph of the left side of cranial cavity, showing the superior petrosal sulcus (P) without any bony
projections. (S) is the shallow sigmoid sulcus without notch .The inferior petrosal sulcus (F) ends at the jugular
foramen (J). (I) is the internal auditory meatus, (O) is foramen ovale, (U) is foramen lacerum, (FM) is foramen
magnum, (C) is the clivus, and (X) is the occipital bone.
Figure 2 (a,b). Photographs of cadaveric cranial cavity showing the cranial nerves labeled as their numbers. (C) is
the internal carotid artery in (a). The two vertebral arteries (R in a & V in b) unite to form the basilar artery (L). The
right sigmoid sinus (S) indents the petromastoid portion of temporal bone, forming a shallow notch (N). Two
medium sized bony projections (arrows) are located between the notch (N) laterally and the right superior petrosal
sulcus (P) medially. Notice that these projections are at the same level superior and inferior to the superior petrosal
sulcus (P) opposite the angle between the sigmoid sinus (S) and transverse sinus (T). Figure (2b) is a close up to the
right half of figure (2a).
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Figure 3. A photograph of the left side of cranial cavity,
showing a large sharp pointed spine (arrow), directed
laterally toward the deep sigmoid sulcus (S) in attempt
of bridging. The superior petrosal sulcus (P) lies medial
to this spine (arrow). (O) is foramen ovale, (U) is
foramen lacerum, (I) is internal auditory meatus, (J) is
jugular foramen, and (FM) is foramen magmun.
509
Figure 4. A photograph of the left side of cranial cavity,
showing multiple small bony projections (arrows) fusing
at their bases and located inferior to the superior petrosal
sulcus (P). The most lateral projection forms a bifid
spine (double headed arrow). A deep notch (N) is lateral
to this spine (double headed arrow). Notice the small
sized emissary foramen (arrow head) at the margin of
the deep sigmoid sulcus (S). (O) is foramen ovale, (U) is
foramen lacerum, and (FM) is foramen magnum.
Figure5 (a,b). Photographs of cranial cavity of the same skull, (a) is the left side and (b) is the right side, showing
single bony elevation in each side (arrow). This projection is small in size in (a) and of medium size in (b). This
bony projection lies between the superior petrosal sulcus (P) medially and the deep sigmoid notch (N) laterally.
Notice that the sigmoid notches (N) are of the same depth on both sides. The medium sized mastoid emissary
foramen (double arrows) opens inside the sigmoid sulcus (S) in (b). (I) is internal auditory meatus, (J) is jugular
foramen, (O) is foramen ovale, and (U) is foramen lacerum.
Figure 6 (a,b). Photographs of left sides of cranial cavities, showing pointed medium sized spine (arrow) medial to
deep sigmoid notch (N). It is directed laterally. The spine lies inferior to the superior petrosal sulcus (P). A small
sized mastoid emissary foramen (double arrows) lies outside the sigmoid sulcus (S) at its upper half in (a) and inside
the sigmoid sulcus (S) at its lower part in (b). (O) is foramen ovale, (U) is foramen lacerum, (I) is internal auditory
meatus, (J) is jugular foramen, and (FM) is foramen magnum.
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Variations Temporal bones Egyptians.
Figure 7. A photograph of the right side of cranial
cavity, showing a medium sized pointed spine (arrow)
directed laterally toward the sigmoid sulcus (S). (N) is a
deep notch lateral to the spine (arrow). A large size
mastoid emissary foramen (double arrows) located
outside the sigmoid sulcus (S). (O) is foramen ovale, (U)
is foramen lacerum, (I) is internal auditory meatus, (J) is
jugular foramen, and (FM) is foramen magnum.
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Figure 8. A photograph of the left side of cranial cavity,
showing a small bony projection (black arrow) above the
superior petrosal sulcus (P), another medium sized
projection (double arrows) lies medial to the deep
sigmoid notch (N). A medium sized emissary foramen
(arrow heads) opens into the sigmoid sulcus. (O) is
foramen ovale, (I) is internal auditory meatus, (J) is
jugular foramen, and (FM) is foramen magnum.
Figure 9 (a,b): Photographs of cranial cavity of the same skull, left side (a) and right side (b), showing the foramen
magnum (FM), the internal auditory meatus (I), the jugular foramen (J), the foramen ovale (O), and the foramen
lacerum (U). (a) Showing medium sized bony elevation (medial arrow) inferior to the superior sulcus (P). Another
medium sized bony elevation (lateral arrow) located medial to shallow sigmoid notch (N). Notice the marked crest
(arrow heads) on the upper margin of the left transverse sulcus (T). (b) Showing multiple bony projections (arrows)
inferior to the superior petrosal sulcus (P), and a medium sized pointed spine (double headed arrow) directed
laterally and separated from the other projections. Notice that the sigmoid notches (N) on both sides are nearly of the
same depth.
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509
Figure 10 (a,b): Photographs of cranial cavity of the same skull, left side (a) and right side (b), showing bilateral
multiple winged spinous projections (arrows) fusing at their bases. These projections are large sized in (a) and small
sized in (b). They are inferior to the superior petrosal sulcus (P). Notice that the sigmoid notch (N) is deeper on the
right side in (b), and the most lateral projection (the most lateral arrow) does not fuse with the other projections in (a
& b). (S) is the sigmoid sulcus.(U) is foramen lacerum, (I) is internal auditory meatus (J) is jugular foramen, and
(FM) is foramen magnum.
Figure 11. A photograph of 3D reconstructed images of
multislice C.T. film of female cranial cavity aged 57
years, showing the transverse sinus (T) which is larger
on the right than on the left. Notice the symmetrical
absence of bony projections or notches in relation to
superior petrosal sulcus (P).
Bull. Alex. Fac. Med. 42 No.2, 2006.
Figure 12. A photograph of 3D reconstructed images of
multislice C.T. film of male cranial cavity aged 24 years.
The left side showing small bony projection (arrow
head) superior to the superior petrosal sulcus (P) and
another two bony projections (arrows) below the
superior petrosal sulcus (P). The medial projection
(medial arrow) in the form of medium sized sharp spine
directed laterally and the lateral one is small simple
elevation. (N) is a shallow left sigmoid notch. Notice the
absence of the notches on the right side.
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Variations Temporal bones Egyptians.
Figure 13. A photograph of 3D reconstructed images of
multislice C.T. film of male cranial cavity aged 60 years.
The left side showing small spine (arrow) lateral to the
superior petrosal sulcus (P). The right side showing a
small bony projection (arrow) lateral to the right
superior petrosal sulcus (P) and medial to a shallow right
sigmoid notch (N).
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Figure 14. A photograph of 3D reconstructed images of
multislice C.T. film of male cranial cavity aged 51 years.
The left side showing medium sized spine (arrow)
medial to the deep sigmoid notch (N) and lateral to the
superior petrosal sulcus (P). Notice the absence of bony
projections or notches on the right side.
Figure 15. A photograph of 3D reconstructed images of multislice C.T. film of male cranial cavity aged 24 years.
The left side showing small bony projection (arrow) lateral to the superior petrosal sulcus (P) and medial to sigmoid
notch (N). the right side showing a shelf like projection (arrow heads) inferior to the superior petrosal sulcus (P) and
forming a sharp medial margin to the deep right sigmoid notch (N). Notice that the sigmoid notch (N) is deeper on
the right. (T) is the transverse sulcus.
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Figure 16a,b. Photographs of 3D reconstructed images of multislice C.T. film of male cranial cavity aged 33 years
in (a) and female cranial cavity aged 18 years in (b).
(a) Showing small spine (arrow) lateral to the left superior petrosal sulcus (P). No bony projections related to the
right superior petrosal sulcus (P). (S) is the sigmoid sulcus.
(b) Showing 2 projections (arrows) lateral to the superior petrosal sulcus (P). The right one is of medium sized while
the left projection is small sized. Notice the absence of sigmoid notches in both skulls (a & b).
DISCUSSION
Bones in general show documented variations in
morphology. The skull is formed of multiple
skeletal elements of different origin so it expresses
numerous variations like unusual ossicles, foramina,
notches, ridges and other non-metrical variations.
The incidence of their existence is used as
anthropological marker to assess different races.(6).
The anatomy of temporal bone has been reported
extensively previously. Despite numerous studies,
detailed variation of its morphology remains unclear
in the published literature. Choudhry et al., 1998
discovered the presence of bony projections related
to the petromastoid part of temporal bone among
Indians.(6)
The purpose of the present study was to document
comprehensively the morphological variations
present on the cerebral aspect of petromastoid part
of temporal bone in adult Egyptian skulls. These
variations were either in the mastoid emissary
foramen related to the sigmoid sulcus, or in
unlabelled bony projections and notches in relation
to the superior petrosal and sigmoid sulci or sinuses,
with particular emphasis on their percentage, site,
side and relation of these variations among Egyptian
population. This study was done on 130 adult
Egyptian temporal bones (60 dried skulls and 5
cadaveric heads). It was found that the percentage of
bony projection on the cerebral aspect of
Bull. Alex. Fac. Med. 42 No.2, 2006.
petromastoid part was 46.15%. They were more
likely to be on the left side than the right (35 left
temporal bones out of 60; 58.33%). It was present
unilateral (66.6%) or bilateral (33.3%).
According to Choudhry et al., 1998 the percentage
of these bony elevations among Indians was
different (15.9%) with prevalence to the right
(59.4%). It was unilateral (72.3%) and bilateral in
27.7%.(6).
Bony projections found in the present study were
either single, double or multiple bony elevations,
they had the shape of simple elevation, spine,
winged spinous process or shelf like projection.
Their approximate sizes were small (62.85% on the
left and 72% on the right), medium (28.57% on the
left and 20% on the right) and large (8.57% on the
left and 8% on the right).
Choudhry et al., 1998 noted that bony elevation
ranged from being inconspicuous tubercles to well
defined sharp spines. A subjective assessment of
size showed the projections to be small (70%),
medium (16%) and large (14%) with predilection for
the right side. They also found that their length
ranged from being barely distinguished by naked eye
to a maximum of approximately 5mm. They
described four large projections, that were slightly
expanded at the bases giving them a winged
appearance. Some of the projections were sharp,
spiny, and directed towards the lateral aspect i.e.
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Variations Temporal bones Egyptians.
(6)
towards the sigmoid sulcus.
Snell, 2004 and Hollinshead and Cornelius, 1985
had encountered such a bony trait as it is depicted in
their illustrations shown as small unlabelled bony
projections unilaterally on the medial aspect of the
sigmoid sulcus.(5,7)
In the present study, these bony projections were
located either superior or inferior to the superior
petrosal sulcus, or on the medial margin of notches
on the cerebral aspect of petromastoid portion of
temporal bone. These notches were found to be
formed by the sigmoid sinus indenting the superior
border of the petrous temporal bone. The sigmoid
sulcus was found to be deeper in some skulls and
shallow in others. This was in agreement with
Choudhry et al., 1998 who stated that the depth of
the sigmoid sulcus was deep and better marked on
the right (81%) than on the left side (19%).
Frequently it notched the superior border of the
petromastoid bone; the depth of the sulcus had no
correlation with the size of the sinus or these bony
entities. The groove for the superior petrosal sinus
was located either superior or inferior to this
projection. In 8 temporal bones a somewhat similar
projection was located about 1cm medial to these
entities; the impression of the superior petrosal sinus
was above it.(6).
Asymmetric variations were usually observed in
the skull. For example, Hatiboglu and Anil; 1992
studied the jugular foramen on Anatolian skulls
from the 17th and 18th centuries. They noted that
the jugular foramen was larger on the right in
61.6% and on the left in 26% with the remainder
being of almost equal size. They reported the
presence of dome caused by the superior
jugular bulb. This dome was present bilaterally
in 49%, on the right in 36%, on the left only in 5%
and it was absent bilaterally in 10%. They also
reported a spicule of bone that leads to separation of
jugular compartment.(8) Asymmetric variations were
observed in the present study by examination of
petrous bone in dried skulls, cadaveric heads and in
patients skulls using a radiological method. Bony
projections and sigmoid notches were present either
on the right side only or on the left side of the same
skull.
In the present work, it was found that the mastoid
emissary foramina had variations both in size and
location. They were small, medium or large. They
opened either inside the sigmoid sulcus, at its margin
or outside the sulcus. It opened into the upper part of
the sulcus or at a lower level. Choudhry et al., 1998
observed that the mastoid emissary foramen of
varying size opened only into the upper part of
sigmoid sulcus.(6)
Basmajan and Slonecker, 1993 reported that one
can find major emissary veins in the posterior aspect
of the occipital condyles and mastoid processes of
temporal bone. These are valveless veins and act as
Bull. Alex. Fac. Med. 42 No.2, 2006.
Monsef.
potential routes by which infections of the scalp
spread to meninges.(9)
The mastoid part of temporal bone is frequently
perforated near its posterior border by the mastoid
foramen, which is traversed by a vein from the
sigmoid sinus and transmits a small branch of
occipital artery to the dura mater; the position and
size of this foramen are variable; it may be situated
in the occipital bone, or in the suture between the
temporal and occipital bones.(3)
Berry, 1975 postulated that the frequency of nonmetrical or minor discontinuous variants of the skull
is inherited by a dominant gene pattern with
incomplete penetrance. Their expression (governed
multigenetically rather than environmentally) is
constant in a given race.(10)
"Iso-incidence lines" for a variant can be mapped
and used for differentiating and comparing
populations. Such an incidence can be attributed to
maternal physiology and diet.(11).
Berry, 1975 found the incidence of many nonmetrical variants of diverse populations and calculated the measures of divergence. These are used
as genetic tools giving a genetic distance in time and
place.(10)
Zindema, 1977 observed small unlabelled bony
projections unilateral on the medial aspect of the
sigmoid sulcus. He diagrammatically illustrated the
attachment of the tentorium cerebelli to these
projections.(12).
In the present work, the results obtained by
radiological scanning were coinciding with those
obtained by gross anatomical examination. It could
be concluded that the bony projections and sigmoid
notches were present in both cadaveric and living
skulls. Thus, they were not post-mortum or
pathological changes and they could be easily
detected preoperatively by using multislice C.T.
scan.
Hollinshead and Cornelius, 1985 reported that the
tentorium cerebelli, the diaphragm of the meningeal
dura mater, is attached to the horizontal part of the
groove of the transverse and sigmoid sinuses. These
sinuses are two parts of the same vascular channel.
They tried to explain the function of the lateral bony
projections as well as the more medially located
supplementary ones. They postulated that the
projections superior or inferior to the superior
petrosal sulcus act as pegs for attachment of the tentshaped tentorium. At the an gulation of the sulcus,
strong retinaculum-like bands of the dura mater
pulling at the bone could form the projections
present on the medial margin of sigmoid sulcus.(7)
This is proved in the present study as the projections
were found at the angle between the sigmoid and
transverse sinuses.
The posterior part of skull base, comprising the
clivus, the petrous temporal bones, and related intra-
Monsef.
Alexandria Bulletin
and extra- cranial structures, is the site of origin or
secondary involvement of several types of benign
and malignant tumors.(13)
The temporal bone is frequently explored in the
surgical approaches to the cerebellopontine angle, so
the surgeon should be familiar with the fine
anatomic features of the cranial aspect of petrous
temporal bone. The surgical approaches must be
tailored to the particular tumor and not the
reverse.(14)
The approach for clival, petroclival and medial
tentorial meningiomas, as well as trigeminal
shwannomas occupying the middle and posterior
fossae necessitate sigmoid sinus ligation.(15)
Clivotentorial meningiomas need an extensive
exposure of clival and petrous regions and their
associated neural and vascular structures. A
combined supra- and infratentorial approach may be
employed by a neuro-surgeon or neuro-otologist. To
connect the supra- and infra-tentorial compartments,
the tentorium has to be dissected.(16)
Incision along the superior petrosal sinus to excise
a tumor at the petrous apex will be curved up
towards the tentorial apex to whatever extent is
necessary to cut through the free tentorium.(17)
The bony projection found in this study may be
encountered during these procedures especially
during dissection of tentorium or ligation of the
sigmoid sinus with clips or sutures. Thus, awareness
of its presence in close proximity to the sigmoid
sinus, superior petrosal sinus and vein of Labbé is of
great surgical importance.(6)
Multislice C.T. is recommended preoperatively to
detect the bony projections or notches related to the
superior border of petrous temporal bone.
Acknowledgement
I would like to express many thanks to Prof. Dr.
Ashraf Etaby, Department of Radio-diagnosis,
Faculty of Medicine, University of Alexandria, for
his great help in the C.T. scanning.
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