ANATOMIC VARIATION OF THE HEIGHT OF THE FALX CEREBRI*

Transcription

1 VOL. zo6, No. 2 ANATOMIC VARIATION OF THE HEIGHT OF THE FALX CEREBRI* ITS RELATIONSHIP TO DISPLACEMENT OF THE ANTERIOR CEREBRAL ARTERY IN FRONTAL SPACE-OCCUPYING LESIONS By F. GALLIGIONI,t R. BERNARDI, and S. MINGRINO A SUPRATENTORIAL space-occupy- A I ing lesion can be diagnosed at carotid PADOVA, angiography by its abnormal circulation or, when this is lacking, by the type of dislocation of arteries and veins it produces. Displacement of the anterior cerebral artery and its branches across the midline represents one of the main features of carotid angiography and its aspects greatly contribute to the diagnosis. It is well known that the shift of the anterior cerebral artery assumes the form of a rounded arc in a case of frontal expansive lesion, and that of a square when the space-occupying lesion is posteriorly placed. Tumoral angiographic picture, however, may occasionally present characteristics which are somewhat different from those considered as typical of expansive lesions of similar size and location. We have observed, for example, cases of frontal expansive lesions producing a square shift of the anterior cerebral artery, which is considered typical of posterior lesions. In most of the cases these abnormal findings can be related to the degree of cerebral edema accompanying the lesion as well as to its nature and to the peculiarity of its location and development. In some cases, however, the explanation of the abnormal angiographic picture can be found in anatomic variation of the intracranial structures which may have a significant relation. It can be conjectured that the type of dislocation across the midline of the anterior cerebral artery and its branches may depend, besides the well known factors, on the amplitude of the hernial hiatus de-. ITALY limited by the falx and the corpus callosum through which herniation occurs. By the peculiarity of its anatomic relationship to the anterior cerebral vessels, a large hernial hiatus represents a condition predisposing to a rounded shift of these arteries, while a narrow hernial hiatus favors a displacement of the square type. Since variations in shape and size of the anterior part of the corpus callosum are minimal,3 the height of the falx cerebri can be considered the main factor in determining the amplitude of the hernial hiatus. The present study was aimed (i) at investigating anatomic variations of the height of the falx cerebri, and (2) at evaluating the importance of these variations in determining different types of displacement of the anterior cerebral artery in frontal expansive lesions. MATERIAL AND METHOD This study is based on 200 selected carotid angiographies of adults where the inferior longitudinal sinus was visualized in lateral projection. Since this sinus is placed in the posterior two thirds of the free margin of the falx, its position served to evaluate the height of the falx cerebri at different points. Krayenbuhl and Yaargil2 found that the inferior longitudinal sinus comes into view in about 59 per cent of carotid angiographies. Various measurements were made in the venous phase of carotid angiography in the lateral view, as shown in Figure i, in order to evaluate the height of the falx at different points. Also, measurements of the * From the Neuroradiological Service, Civil Hospital of Padua, t and the Institutes of Radiology, and Neurosurgery, University of Padua, Padova, Italy. 273

2 274 F. Galligioni, R. Bernardi and S. Mingrino JUNE, 1969 FIG. i. Schematic drawing showing the technique of measurements. A. Distance between the tuberculum sellae (ts.) and the internal surface of the skull at the bregma. (a) Distance from the internal surface of the skull to the inferior longitudinal sinus (ils.) along line A. B. Distance between the tuberculum sellae and the internal surface of the skull forming an angle of 30#{176} posterior to line A. (b) Distance from the internal surface of the skull to the ils. along line B. C. Distance between the ts. and the internal surface of the skull along a line crossing the proximal end of the vein of Galen. (c) Distance between the internal surface of the skull and the ils. along line C. (d) Distance from the ts. to the venous angle where the thalamostriate and septal veins join the internal cerebral vein. height of the venous angle and of the height of the skull were made searching for their possible relationship to falx size. In addition, 3 cases are presented of frontal glioma verified at surgery, with masses of similar size and corresponding location, which showed different types of anterior cerebral shift. RESULTS The results of falx measurements are summarized in Table I. Frequent and sometimes marked individual variations in the height of the falx cerebri were found, ranging from 28 to 48 mm. anteriorly, from 41 to 62 mm. at the middle and from 40 to 62 mm. at the posterior points. The height of the falx was compared with the corresponding height of the skull measured from the tuberculum sellae, but no significant relationship was found between the two categories of measurements. Similarly, no relationship was detected between the height of the falx and the distance of the

3 VOL. io6, No. I Height of the Falx Cerebri 275 TABLE I ANATOMIC VARIATION OF THE HEIGHT OF THE FALX CEREBRI Minimal (cm.) Maximal (cm.) Distance from tuberculum sellae to bregma (A) 8. 6 ii Distance from ts. to skull (B) 10.5 i Distance from ts. to skull (C) Height of falx cerebri in (a) Height of falx cerebri in (b) Height of falx cerebri in (c) Distance from ts. to venous angle (d) P L Mean (cm.) 1 Iii I / 1 fl tal 1(111 [ ii tii in rnii r( 1111 cl.iil ft nt tic [fl tcn( r ccrchral artcrv. ( i IIlc ntcrl(r!unlilttliliia! sinus Irruws is Iiii.ihcr than tvc atic. the ta! \ lilcisi rc 4.1, an! c.o eta, at the standard 1 jilts 1, Ii, and c, rcspccti ye! c. A

4 276 F. Galligioni, R. Bernardi and S. Mingrino JUNE, 1969 venous angle from the tuberculum sellae, ranging from 32 to 54 mm.; a low venous angle was not associated with a large falx and, vice versa, a high venous angle was not related to a narrow falx. These measurements bring into evidence the primary variation in the size of the falx, independently of skull dimensions, and thus of the interspace between the falx and the corpus callosum. Consequently, different amplitudes of the hernial hiatus may contribute to explain the various types of t(,.. (.1 and Th trontal Ldioma ii itli squire sh itt of the anterior cerebra! artery. ( (d l he arrows point to the interior longitudinal sinus s Inch is rather ow and en- Iariei. siiice it drains Venous blood tr( ni tie lesion. Ilie falx iieasttre nients are ci, in! (. em., re- SI)eCti ye!. anterior cerebral artery shift in cases of frontal expansive lesions. One of the 3 cases presented showed a rounded shift of the anterior cerebral artery (Fig. 2, 11-C), while the other 2 exhibited a square shift (Fig. 3, il-c; and, 11-C). In the case with typical, rounded shift the falx measurements were 32, 41, and 50 mm. at the anterior, middle and posterior points, respectively, which are below average, indicating a large hiatus. The cases with abnormal, square shift had a rather

5 VOL. xo6, No. 2 Height of the Falx Cerebri 277 large faix, showing measurements of 39, i, and 68 mm.; and 3, 6o, and 54 mm., respectively, well above average, which narrowed significantly the hiatus. Similar abnormal features have been observed in several other cases. It thus appears that when the falx is large, the possibility of displacement of the anterior cerebral artery across the midline is limited by a narrow hiatus. The resulting shift of a frontal expansive lesion is a to. 4. (.l in! I?) :\nother example (If anomalous 5Iar shift ot the anteriot cerebral artery in a case ot huge trontal glioma. ) (.d the interior longitudinal sinus, indicated b the arrows, shows i large ft!x (4., lq, an! Ciii., respective! vi. limited arc with steps at one or more points, similar to the square shift of posterior lesions. Conversely, if the hiatus is large, it is possible that even posterior lesions may cause anterior cerebral artery shift with rounded arc and no steps at any arterial segment, similar to that observed in frontal expansive lesions. This remains hypothetical, however, as we have not seen such a picture as yet.

6 278 F. Galligioni, R. Bernardi and S. Mingrino JUNE, 1969 These observations are not intended to ascribe the height of the falx cerebri and related cerebral artery shift a particular, definite value. A correct diagnosis must be based upon several factors and not limited to a single angiographic picture. However, knowledge of tf., various elements that may influence the type of dislocation of the anterior cerebral artery across the midline is useful and contributes to a better understanding of abnormal angiographic pictures whose interpretation may seem uncertain and difficult at first sight. SUMMARY Differences in the height of the falx cerebri are demonstrated. Abnormal anterior cerebral artery shift of frontal space-occupying lesions may be related, besides the well known factors such as degree of coexisting edema and peculiar location of the lesion, to these anatomic variations of the falx cerebri. Dr. S. Mingrino Istituto di Neurochirurgia Via Guistiniani, 35I00 Padova, Italy REFERENCES I. JOHAN5ON, C. Central veins and deep dural sinuses of brain: anatomical and angiographic study. Acta radiol., 1954, Suppl KRAYENB#{220}HL, H., and YAARGIL, M. G. Die Zerebrale Angiographie. Georg Thieme Verlag, Stuttgart, 1965, pp MCRAE, D. L., and CA5TORINA, G. Variations in corpus callosum, septum pellucidum and fornix, and their effect on encephalogram and cerebral angiogram. Acta radiol. (Diag.), 1963, i, o.

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