Articulo anexado Karen Alejos

A NOTE ON SYMMETRICAL THINNING OF
THE PARIETAL BONES
BY ARCHIBALD DURWARD, M.B., CH.B.
(From the Department of Anatomy, University of Otago, New Zealand)
INTRODUCTION
IN the museum of this department there are now five skulls exhibiting the
condition known as "Symmetrical thinning of the parietal bones."
Although Elliot Smith(2) found the condition to be relatively common in
Egyptian cemeteries of certain dynasties, the literature does not suggest that
to-day symmetrical thinning is at all common. Sir George Humphry(4) had
located six specimens in European museums in 1858, and mentioned two others
of a doubtful nature. Since that time little has been heard as to the frequency
of the condition; but one can hardly suppose that museums possessing large
osteological collections can be devoid of examples. Perhaps this reference to
''symmetrical thinning" may lead to further information from other sources
concerning this very definite, though puzzling, condition.
Examination of about 1000 skulls, both in the dissecting-room and in the
museum collection of Maori and Moriori skulls, has yielded five cases of symmetrical
thinning-a frequency of approximately 1 in 200. This would appear
to be a higher rate of frequency than Humphry had noted in European
museums. In 400 Maori and Moriori skulls examined only one case was found.
Two of the cases reported belonged to Chinese, but the number of Chinese
dissected here, 25 to date, is so limited that conclusions cannot fairly be drawn
from this fact.
DESCRIPTION OF CASES
In all cases the process of thinning has operated entirely from without,
affecting the outer table and the diploe most constantly. The inner table has,
however, been definitely involved in one case (fig. 2) where a perforation has
resulted. In no case does the interior of the skull show any abnormality. The
condition affects that portion of the parietal between the sagittal suture and
the temporal ridge and is about equidistant from both coronal and lambdoid
sutures.
The symmetrical nature of the condition is very apparent in all cases,
though there may be, as in the skull shown in fig. 3, a difference in the extent
of the thinning on the two sides both as to the area of bone involved and the
depth of the thinning.
The edges have a characteristic shelving nature so that usually a fairly
wide rim of diploe surrounds the central area of exposed inner table. In one
Coronal Sutu|
ridge
Diploe -
expose
Fig. 1. Skull of a male subject from the dissecting room. The sutures are largely obliterated. The
proximity of the thinning to the temporalJridge is evident. The inner table presents a smooth
surface compared with the finely nodular surface of the exposed diploe.
Diploe _ _
exposed
Perforation -= n ne
La ~Ie
Lambdoid suture
Fig. 2. This skull, removed from the dissecting room, has the sutures almost completely obliterated.
Sex not recorded. On the left side the thinning has proceeded so far as to expose the
grooves for meningeal vessels in the interior of the skull, an irregular perforation resulting.
Other minute foramina exist on both sides leading into the grooves for meningeal vessels.
Archibald Durward
case (fig. 5), which is somewhat atypical, the shelving nature of the edge is
not so apparent and the diploe is not exposed at all, but the symmetrical
nature of the condition and its position on the bone are typical.
Both the size and the contour of the areas involved vary very considerably
in the different cases of this series, but in every skull the lateral border of the
thinned area lies closely against the temporal ridge. In those cases which
present a considerable area of thinning (figs. 1, 2, and 3) the lateral border
skirts round the temporal ridge in a remarkable manner, and the shelving edge
on this aspect is as a rule much steeper than the edge elsewhere. In no case
does the thinning extend beyond the temporal ridge, and as shown in the
figures the parietal foramina, when present, are not involved.
In the better marked cases the areas of thinning are plainly seen with
transmitted light, and where the grooves for meningeal vessels have crossed
the field the thinning is very clearly accentuated.
DISCUSSION
Sir George Humphry(4) described the condition briefly in its typical form,
mentioning that it is situated midway between the sagittal suture and the
parietal eminence, and that the parietal ¶oramina always escape. In this series
the areas of thinning would certainly appear to lie nearer the parietal eminence
than Humphry found. From the symmetrical nature of the process and from
the absence of disease in the specimens he examined, Humphry considered the
thinning to be of a congenital nature. He had, moreover, seen a case in a living
child, a fact which supported the suggestion of the congenital nature of the
condition. In another place (5) Humphry suggested as a possible causal factor
the pressure of the occipito-frontalis; but this does not seem likely in view of
the very definitely localised areas .of thinning.
Elliot Smith (2) had the opportunity of examining over 70 examples of this
condition in Egyptian skulls, and from the fact that the thinning was present
only in the skulls of the wealthy of certain dynasties when heavy wigs were
apparently worn continuously, he concluded that continuous pressure from
the exterior, with its resultant interference with the blood supply to the bone,
was probably the causative factor. From the skulls he examined he was able
to show definitely that the condition was not necessarily a senile one and that
both sexes were affected. The thinning appeared to have taken place by erosion
of a properly developed cranial wall, and moreover there was not a single
instance of its occurrence in an individual under 25, or perhaps even 30, years
of age. For the Egyptian cases, then, it appears clear that the condition was
not congenital and that it had as its cause continuous pressure from the exterior.
Shepherd (8) also describes the typical form of the condition and records
three cases one of which, an adult female, was in the living. In this latter case
the evidence pointed strongly to the congenital nature of the condition, and
there was a suggestion also of its being hereditary. Shepherd mentions senile
358
Symmetrical Thinning of the Parietal Bones
Temporal ridge Outline of
meningeal
vessel
Fig. 3. Skull of a male Chinese, aged 74, from the dissecting room. The sutures are largely obliterated.
On the left side the thinning has proceeded no further than to expose the diploe.
Tempordl
ridge
Diploe
Fig. 4. Skull of a male Chinese, aged 74, from the dissecting room. All sutures closed. The areas
of thinning are small and shallow, the inner table being nowhere uncovered.
359
Archibald Durward
changes in the temporal artery as a possible causal factor, leading to atrophy
of the outer table and the diploe, but leaving the inner table unaffected. He
notes that this cannot explain all cases.
The condition is referred to by Maier(6) and Ziegler (9), both of whom regard
it as a senile change.
There is the possibility that if this condition be progressive, it may ultimately
lead to symmetrical perforations. Greig (3), Derry (1), and Paterson and
Lovegrove (7) have written of parietal perforations. While Greig and Derry do
not mention symmetrical thinning, Paterson and Lovegrove draw attention
to it and state that there is no apparent relationship between symmetrical
thinning and such perforation as they described. One skull of the series
described in this paper (fig. 2) shows a perforation on one side, but it is not of
the type figured by these writers; it has obviously resulted from the thinning
process meeting the grooves for the meningeal vessels. Paterson and Lovegrove
also state that they have seen symmetrical depressions in foetal parietal bones.
Reviewing the various causes that have been suggested, certain of them
may be discounted when applied to the skulls of this series. Continuous
pressure from some external object, which adequately explains the Egyptian
cases described by Elliot Smith, will not explain the cases of this series where
no history of pressure of such a type is forthcoming. Humphry's suggestion
of pressure from the occipito-frontalis does not appear to be sufficient in view
of the definitely localised areas of bone involved in this series.
It would certainly appear that the condition is most frequently met in aged
skulls, and the view that it is really a senile change has had not a few supporters.
But Elliot Smith found the condition in relatively young skulls in
Egypt; also there are cases on record of its occurrence in the living of such ages
that senile changes may be safely excluded; and one skull of this series (fig. 5)
is certainly not senile. These facts prove that, though the condition is commonest
in advanced life, it is not necessarily a senile change.
Humphry, Shepherd, and Paterson and Lovegrove have all mentioned the
likelihood of the condition being congenital, and the former two writers
reported cases in the living which were suggestive of being congenital. Though
this is not so convincing as the production of the actual skull, yet it must be
admitted as a possibility. Elliot Smith did not consider it likely to be congenital
so far as the Egyptian skulls were concerned. In view of these facts,
then, it must be admitted that, however likely this suggestion may be, direct
proof is lacking.
The possibility of symmetrical thinning of the parietal bones being a progressive
condition appears not unlikely. The most constant position of the
thinning is just above the temporal ridge and about midway from before back
on the bone. From this spot spread would take place forwards, medially
towards the sagittal suture, and backwards, and also the thinning would
become progressively deeper. This would account for the varying areas of
thinning met in different skulls. The constant proximity to the temporal ridge
360
Symmetrical Thinning of the Parietal Bones 3
seems certainly to have some significance. The blood supply to the bone would
be assured from the level of the temporal ridge downwards owing to fascial
and muscular attachments, whereas above this level the nourishment of the
bone would not be assured by any such attachment. The possibility exists
therefore that the condition may be progressive and that it may depend upon
some deficiency in the blood supply. No cause for this deficiency which would
account for all the cases of this series is evident.
TempordI
BIse formed
byouter tdble
Fig. 5. Maori skull with all sutures open; over 25 years of age. The diploe is not exposed and the
edges are not so typically shelving as in the other cases.
SUMMARY
1. Five cases of symmetrical thinning of the parietal bones are described.
2. The literature available is briefly reviewed and existing theories as to
causation are mentioned.
3. The constant proximity of the thinning to the temporal ridge in the
cases of this series is stressed.
4. It is suggested that the condition may be progressive, and that it may
be caused by a deficiency in the blood supply to the bone above the level of
the temporal ridge. No cause for such deficiency is suggested.
In conclusion I wish to express my thanks to Prof. W. P. Gowland for
permission to publish the cases which have occurred in the Museum and in the
dissecting-room of this department.
361
362 Archibald Durward
REFERENCES
(1) DERRY, D. E. (1914). Journ. of Anat. and Physiol. xLVII. p. 417.
(2) ELLIOT SMITH, G. (1907). Journ. of Anat. and Phy8siol. xII. p. 232.
(3) GREIG, D. M. (1892). Journ. of Anat. and Phyiol. xxvi. p. 187.
(4) HuxpEuy, G. (1858). The Human Skeeton. Cambridge. Pp. 242-243.
(5) - (1890). Journ. of Anat. and Phy8iol. xxrv. p. 598.
(6) MAIER. Virchow'8 Archiv, vIi. p. 336. (Quoted by ELLIOT SMITE.)
(7) PATERSoN, A. M. and LOVEGROVE, F. T. (1900). Journ. of Anac. and Phy8iol. xxxiv. p. 228.
(8) SHEPHERD, F. J. (1893). Journ. of Anat. and Phy8iol. xxvir. p. 501.
(9) ZIEGLER. Text Book of Special Pathological Anatomy, transl. MACALsSTER and CATTELL, 1896,
sections i-viii, p. 143. (Quoted by ELLIOT SmX[T.)