770 MARCHAU Neurosurgery, Vol. 23, No. 6 Fic. 2. 4: CT scan. B: Schema—the cross hatched parts are displaced fragments from the orbital roof. The normal configuration of the orbital cave is single hatched. parenchyma of the brain surrounded by hypodensity. A marked hyperdensity of the falx cerebri was interpreted as a congestion or thrombosis of the sinus sagittalis superior. We noted the presence of pneumoencephaly. More peculiar was the scan of the orbits (see Figs. 1 and 2). We noted an elongation and protrusion of the eyeballs. Loose fragments of bone from the orbital roof protruded down into both orbits, and the perinasal sinuses were filled with blood and fluid. EXPLICATION OF THE EXPLOSION PHENOMENON The meninges and the brain are protected from harmful external stimuli, including electric current, by the ossae cal- variae and the skin. Prolonged contact with high voltage electric current causes burning of the skin and calcinosis or even fracture of the skull. The passage of electric current results in an input of energy into the brain with heating, edema, extravasation of blood, heating of the cerebrospinal fluid, and the production of steam. 0148-396X/88/2306-0770802.00/0 NEUROSURGERY Copyright © 1988 by the Congress of Neurological Surgeons The heating and steam production have an explosive effect and the weakest part of the skull may be disrupted, i.e., the laminae cribrosae and the orbital roofs. The displaced and fragmented orbital roof may protrude into the orbits along with brain substance. A similar case was reported by Fritz in 1941 (1). Received for publication, May 9, 1988; accepted, June 29, 1988. Reprint requests: Marcel Marchau, M.B., Generaal Lemanlaan 30, B.8320 Brugge 4, Belgium. REFERENCES 1. Fritz E: Eigenartige Befunde bei Einwirkung electrischen Stro- men gegen den Schidel. Deutsch Z Gerichl Med 34:177, 1941. . Gerhard L: Elektrotrauma und Blitzschlag, in Neurologie in Praxis und Klinik. Stuttgart, Georg Thieme, 1983, vol 1, no. 3, pp 105. 3. Petty PG, Parkin G: Electrical injury to the central nervous system. Neurosurgery 19:282-284, 1986. N Vol. 23, No. 6, 1988 Printed in U.S.A. Intrasellar Intercarotid Communicating Artery Associated with Agenesis of the Right Internal Carotid Artery: Case Report Masahiko Udzura, M.D., Hiroo Kobayashi, M.D., Yoshio Taguchi, M.D., and Hiroaki Sekino, M.D. Department of Neurosurgery, St. Marianna University School of Medicine, Kawasaki, Japan A 54-year-old man with a right hemiparesis was found to have an intrasellar intercarotid communicating artery associated with agenesis of the right internal carotid artery. Magnetic resonance imaging (MRI) studies demonstrated the spatial relationship of the anomalous artery to the surrounding structures, thus suggesting an embryonic enlargement of the capsular artery as a source of this anomalous artery. (Neurosurgery 23:770-773, 1988) Key words: Agenesis, Capsular artery, Collateral artery, Internal carotid artery, Sella turcica December 1988 Unilateral agenesis of the internal carotid artery is a rare anomaly. In the majority of reported cases, collateral circu- lation to the intracranial arteries is from the contralateral internal carotid artery and the vertebrobasilar system via the circle of Willis. Very rarely, blood is carried to the affected side through an anomalous artery between the cavernous part of the two internal carotid arteries. To our knowledge, only 10 cases have been reported in the literature, although none had magnetic resonance imaging (MRI) studies that demon- strated the spatial relationship of this anomalous artery to the surrounding structures. We report a case of unilateral agenesis of internal carotid artery associated with an unusual transsel- lar intercarotid connection being demonstrated by MRI. CASE REPORT A 54-year-old, right-handed man was admitted to our hos- pital with sudden onset of right motor weakness 2 months Fic. 1, Plain x-ray film of the sella turcica, lateral projection, showing an area of focal scalloping in the floor. INTRASELLAR INTERCAROTID COMMUNICATING ARTERY 771 before admission. His medical history revealed a subtotal gastrectomy because of early stage gastric cancer 14 years previously and diabetes mellitus for which he had been treated with sulfonyl ureas for 2 years. No other vascular risk factors were found. Routine skull roentgenograms showed a depression of the sellar floor (Fig. 1). A cranial computed tomography (CT) scan revealed small low density areas in the left basal ganglia and the posterior limb of the left internal capsule. No other abnormalities were shown even in the postcontrast study including around the sella turcica. Arch aortogram with trans- femoral digital subtraction angiography showed normal origins and courses of the left common carotid artery and the left vertebral artery. No other remarkable findings were pres- ent except for a relatively small-sized right common carotid artery. The transfemoral right carotid angiogram revealed no filling of the internal carotid artery and only the external carotid artery filled with no transdural collateral circulation. The left carotid angiogram seemed normal in its extracranial portion, but an anomalous artery, originating from the cav- ernous portion, served as the main collateral circulation to the right middle cerebral artery. The A; portion of the right anterior cerebral artery was not filled, and the left carotid Fic. 3. CT scan of the skull base showing an absent right carotid canal and an enlarged left carotid canal. il & Fic. 2. Left carotid angiogram. The anteroposterior (4) and lateral (B) views demonstrate an anomalous artery (arrows) that originated from the cavernous portion and serves as the collateral circulation to the right middle cerebral artery. 772 UDZURA et al. artery provided bilateral anterior cerebral artery circulation (Fig. 2). The vertebral angiograms showed normal configuration without filling of the posterior communicating and carotid arteries. Basal skull CT scan disclosed the absence of the right carotid canal and an enlarged left carotid canal, thus suggest- ing agenesis of the right internal carotid artery (Fig. 3). MRI was informative (Fig. 4). The T,-weighted (TR/TE = 500/40, 0.15 Tesla) midsagittal view demonstrated a round low inten- sity area corresponding to the anomalous artery anteroinferior to the normal pituitary gland. The horizontal course of this artery underneath the pituitary gland was also clearly shown in the coronal view with the same imaging protocol. DISCUSSION This case demonstrated the absence of the right internal carotid artery with collateral circulation via an anomalous communicating artery between the intracavernous portion of the internal carotid arteries. Lie was the first to describe this type of anomaly in an epileptic child (6), and there have been ten similar cases in the literature (1-6, 9-11). All of these anomalous arteries were found incidentally by conventional radiological studies. No case has been considered as a cause of neurological deficit. Our case had multiple small infarcts in the basal ganglia and internal capsule, showing right hemiparesis; however, no def- inite corresponding lesion was shown in the arch aortogram and left carotid angiogram. Furthermore, this anomalous artery did not seem to be a thromboembolic source because blood is carried to the side of cerebral infarct through the normal internal carotid artery. Although the pathogenesis of the cerebral infarcts remains unclear, diabetes mellitus may play a major role. The embryogenesis of this anomaly is open to interpreta- tion. Because agenesis of the internal carotid artery is a developmental anomaly that occurs before the embryo Neurosurgery, Vol. 23, No. 6 reaches 24 mm (7), there is no question that this intercarotid anastomosis develops before the sixth week of embryological growth. Lie postulated that this anastomosis resulted from the fusion of two primitive trigeminal arteries because of its location near the trigeminal ganglion (6). In most of the reported cases, however, including ours (1, 3-5, 9-11), the intercarotid communicating artery extended across the sellar floor. Elefante et al. (1), described that the two primitive maxillary arteries were likely to remain and develop as an intercarotid anastomotic artery. According to the embryolog- ical studies of Padget (7), the primitive maxillary artery orig- inates from the cavernous portion of the internal carotid artery lateral to the base of Rathke’s pouch in the 3- to 4-mm embryo. Normally, this artery involutes, and only the stem remains by the 24-mm stage of embryonic growth. This stem is incorporated into the formation of the inferior hypophyseal artery. In a study of over 200 cadavers, Parkinson reviewed the anatomy of the circulation in the area surrounding the sella turcica (8). There are some anastomoses between the two internal carotid arteries. The capsular arteries and inferior hypophyseal arteries are within the sella turcica. The remain- ing intercarotid anastomosis is found at a greater distance down the clivus. The anastomosis between the two inferior hypophyseal arteries occurs on the posterior surface of the posterior lobe of the pituitary gland, which formed the ante- rior part of the circulus arteriosus around the root of the dorsum sellae. The capsular artery leaves the inferomedial aspect of the internal carotid artery 2 to 3 mm anterior to the origin of the meningohypophyseal trunk and anastomoses with its counterpart extradurally within the sella turcica. In this case, the spatial relationship of the anomalous artery to the surrounding structure was clearly shown by MRI. This artery is located anteroinferior to the normal pituitary gland in the sella turcica. Based on these MRI studies, embryonic enlargement of the capsular artery seems to be a more likely source of this anomalous artery than development of primi- d Fic. 4. Magnetic resonance images (TR/TE = 500/40, 0.15 Tesla). The coronal (4) and midsagittal (B) views demonstrate a low intensity area (arrows) corresponding to the anomalous artery anteroinferior to the normal pituitary gland. December 1988 tive maxillary artery or inferior hypophyseal artery as pro- posed by Janicki et al. (4). Although the intrasellar intercarotid communicating artery is extremely rare, knowledge of the presence of this anomaly is important when considering cerebrovascular surgery or transsphenoidal pituitary surgery. Received for publication, April 19, 1988; accepted, final form, June 14, 1988. Reprint requests: Yoshio Taguchi, M.D., Department of Neuro- surgery, St Marianna University School of Medicine, 2-16-1 Sugao Miyamae-ku Kawasaki, Kanagawa, Japan. REFERENCES 1. Elefante R, Fucci G, Granata F, Graziussi G, Smaltino F: Agen- esis of the right internal carotid artery with an unusual transsellar intracavernous intracarotid connection. Am J Neuroradiol 4:88- 89, 1983. 2. Faivre J, Vallée B, Carsin M, Scarabin JM, Simon J: Agenesis of the cervical and petrosal portions of the left internal carotid artery. J Neuroradiol 5:133-138, 1978. 3. Harispe L, Creissard P, Martinez G, Metzger J: Une artére communicante anormale unissant les deux artéres carotides in- ternes intracraniennes. J Radiol Electrol Med Nucl 51:759-762, 1970. 4, Janicki PC, Limbacher JP, Gunito FC Jr: Agenesis of the internal carotid artery with a primitive transsellar communicating artery. AJR 132:130-132, 1979. 5. Kishore PRS, Kaufman AB, Melichar FA: Intrasellar carotid anastomosis simulating pituitary microadenoma. Radiology 132:381-383, 1979. 6. Lie TA: Congenital Anomalies of the Carotid Arteries. Amster- dam, Excerpta Medica, 1968, pp 44-49. 7. Padget DH: The development of the cranial arteries in the human embryo. Contrib Embryol 32:205-261, 1948. 8. Parkinson D: Collateral circulation of cavernous carotid artery: Anatomy. Can J Surg 7:251-268, 1964. 9. Schmidt RC: Partielle Aplasie der rechten Arteria carotis interna mit einer ungewohnlichen Kollateralarterie unterhalb der Hy- pophyse. Fortschr R6ntgenstr 130:572-575, 1979. 10. Smith PR, Kees CJ, Hogg ID: Agenesis of the internal carotid artery with an unusual primitive collateral: Case report. J Neu- rosurg 37:460-462, 1972. 11. Staples GS: Transellar intracavernous intercarotid collateral ar- tery associated with agenesis of the internal carotid artery. J Neurosurg 50:393-394, 1979. COMMENTS The authors present an unusual arterial anomaly that crosses through the sella. This case illustrates the adaptability of collateral circulation particularly during early development. The absence of a carotid canal is strong evidence to support an early developmental abnormality. The authors give a strong argument in favor of the capsular artery as the source of this anomaly. The report also makes the neurosurgeon involved with transsphenoidal operations aware of the potential for arterial anomalies that could threaten the intracranial circulation if interrupted. It under- INTRASELLAR INTERCAROTID COMMUNICATING ARTERY 773 scores the need to image the basic vascular anatomy surround- ing the sella before operations with either the usage of MRI or angiography. Kalmon D. Post New York, New York The article by Udzura and colleagues provides an excellent description of a case of agenesis of the right internal carotid artery with a large intrasellar intercarotid communicating artery. The role of modern imaging techniques in the char- acterization of this rare anomaly is appropriately highlighted. Specifically, the CT scan of the base of the skull allows adequate evaluation of the bony carotid canal. The MRI provides complementary information by demonstrating the presence or absence of large vascular structures, which would appear as channels of signal void. As in most previously reported cases of this rare entity, the anomaly was discovered incidentally. In this case, the patient presented with lacunar infarctions most likely unrelated to the vascular anomaly. Occasionally, agenesis of the internal carotid artery may become significant in the presence of contralateral hemodynamic lesions. Also, the abnormal col- lateral vessels may rarely serve as channels of embolism from contralateral ulcerated lesions. We concur with the authors’ anatomic description and embryological analysis of this anomaly. Because of its anterior inferior relationship to the hypophysis, it is unlikely that the major collateral artery represents connections between trigem- inal, tentorial, maxillary, or inferior hypophyseal arteries. Instead, it is most likely a dilated connection between hyper- trophied inferior capsular arteries. Such arteries are the most distal and least constant set of branches arising from the intracavernous internal carotid artery. They are found in slightly less than 30% of adult anatomic specimens and are known as McConnell’s capsular arteries (Harris and Rhoton, J Neurosurg 45:169-180, 1976). Another peculiar feature of this case is the incompetent anterior and posterior circle of Willis as demonstrated angio- graphically. The channels of the circle of Willis are typically hypertrophied in cases of agenesis of the internal carotid artery. In this case, the circle of Willis abnormalities must have antedated the intercavernous collateral channel embry- ologically and may have provided the hemodynamic incentive for the persistence of this primitive artery during develop- ment. One must not ignore another important potential source of collateral circulation to the right middle cerebral artery territory; i.e., the right ophthalmic artery. The authors mention the absence of transdural collaterals upon right ex- ternal carotid artery injection, but do not mention the pres- ence or absence of retrograde ophthalmic artery filling. This information would have been essential if there was any ques- tion about hemodynamic compromise. Issam A. Awad John R. Little Cleveland, Ohio