Neurosurgical forum hemispheric brain swelling, as was shown in studies by our group, 3 as well as others. It is clearly hindsight, after being aware of our results on the limited significance of LT's, to arrive now at the conclusion that "The contribution of LT's alone to this acute, biochemically complex, and massive edema response is unlikely to be significant." The statement "Since hemorrhagic necrosis is also caused by the freeze lesion, it is perhaps a little simplistic to expect to find a significant difference in the amount of hemispheric swelling.., with and without BW755C... " is in itself simplistic because it rigorously precludes the possibility that brain swelling from a freeze lesion can be therapeutically influenced. This, however, is not the case, as demonstrated by abounding experimental and clinical evidence. 4. Our recent article does not mention or discuss a possible contribution of a parietal craniotomy to hemispheric swelling. In fact, we have performed a series of sham operations on control animals where we could not observe hemispheric swelling due to the craniotomy. In this series of 10 animals, the mean difference in weight between the right and left hemisphere was 0.018 _ 0.042 gm, which would account for a theoretical swelling of 0.12% _+ 0.47%. Since the animals were bled at the end of the experiments, blood volume did not affect hemispheric swelling. It is correct that intraparenchymal hemorrhage and extravasation of plasma proteins contribute to differences in hemispheric wet weight. This, however, can be taken into account when looking at the differences in hemispheric dry weight. In fact, neither factor significantly affected hemispheric swelling. ANDREASUNTERBERG,M.D.

Free University of Berlin Berlin, Germany ALEXANDERBAETHMANN,M.D. Ludwigs-Maximilians-University Munich, Germany References

1. Black KL, King WA, lkezaki K: Selective opening of the blood-tumor barrier by intracarotid infusion of leukotfiene C4. J Neurosurg 72:912-916, 1990 2. Unterberg A, Baethmann A, Wahl M, et al: New aspects in the formation of vasogenicbrain edema, in Baethmann A, Messmer K (eds): Surgical Research. Recent Concepts and Results. Heidelberg: Springer-Verlag, 1987, pp 3-8 3. Unterberg A, Dautermann C, Baethmann A, et al: The kallikrein-kinin systemas mediator in vasogenicbrain edema. Part 3: Inhibition of the kallikrein-kinin system in traumatic brain swelling. J Neurosurg 64:269-276, 1986 4. Unterberg A, Polk T, Ellis E, et al: Enhancement of infusion-induced brain edema by mediator compounds, in Long DM (ed): Brain Edema. Advances in Neurology, Voi 52. New York: Raven Press, 1990, pp 355-358

Cavernous Sinus Exploration

To Trt~ EDITOR: The article by van Loveren, et at., is a beautiful anatomical work (van Loveren HR, Keller

J. Neurosurg. / Volume 76/February, 1992

JT, E1-Kalliny M, et al: The Dolenc technique for cavernous sinus explorgdon (cadaveric prosection). Technical note. J Neurosurg 74:837-844, May, 1991). A cursory glance at the frontispiece gives the impression that the parasellar venous arrangement is one large space. But on close inspection Batson's cast, as touched up by the artist, shows the fine detail of the parasellar plexus in a few areas on the periphery where the veins are not superimposed. In a two-dimensional projection, the result of the superimposition is the appearance of a mass, just as plain film angiograms show only a parasellar"blob," whereas stereographic angiograms of good quality will show the plexus of veins in the parasellar region. Nevertheless, the frontispiece shows the marked contrast between those veins in the parasellar plexus and the smooth regular surface of the true sinuses visualized on the right. It also demonstrates that the carotid artery is incompletely surrounded (although drawn in later by the artist). The artist has indicated much more venous bulk in front of the caroti d syphon on the right than actually exists. Discrete venous channels are demonstrated beautifully in Figs. 4, 7, 8, and 9. The artist has drawn the fourth nerve hanging down in a bow as it will when dissected free from all of its attachments, but in silu it remains up in the roof of this compartment along with the third nerve. (That triangle is narrow enough as it is!) The fourth nerve is slightly pulled laterally in Figs. 8, 9, and 10. Although we used Batson's injection material (No. 14, I believe), I was unaware of his casts of this region. Hunter's superb casts showing the parasellar venous plexus in great detail in infants are still beautifully preserved in the Hunterian Museum.* This anatomy apparently was overlooked immediately after Winslow 6 gave the name "cavernous sinus" to this compartment, just as the description and drawing by Monro Primus ~ of the connection of the carotid sympathetic nerve to the sixth cranial nerve in this compartment has been overlooked. I only wish that the name could be changed. This compartment bears no resemblance at all to the venous anatomy of the corpora cavernosa of the penis for which it was named? The compartment is not a venous cavern, certainly not a single venous channel of any sort, and not a true sinus in the sense of the other named intracranial sinuses. The term misleads people into thinking that if entered it will bleed excessively, yet those who remember posterior root section surgery know that the bleeding is easily controlled with small pledglets as with any other venous bleeding. Any tumor arising within the compartment will obliterate these veins. The venous plexus is continuous, without change in character, with the veins of the dorsum sellae and the orbital veins. One modem text has accurate pictures of the venous anatomy 4 and another acknowledges that it is probably a plexus of veins? * Hunterian Museum, specimens K-429-11, and Wellcome Museum, specimen K-429, Royal College of Surgeons Building, London, England. 341

Neurosurgical forum It is very gratifying to find more and more surgeons familiarizing themselves with the lateral sellar compartment commonly called the "cavernous sinus." Twentyfive years ago it seemed no one would ever again operate in this compartment as balloon catheters were taking over. Then came the magnificent work of Dolenc and his disciples, among which the Cincinnati group are now numbered. The authors are crediting us with an extra year of priority. Just to set the record straight, although we worked out the collateral arteries and the other anatomy in 1963 and presented them at a Royal College of Physicians and Surgeons meeting in Canada, the first publication of the anatomy was 1964. 2 The 1963 article by myself and the ophthalmologist Ramsey 3 that they cited concerned the case that told me there must be a collateral vessel normally available to the parasellar carotid arteries. DWIGItT PARKINSON, M.D.

The University of Manitoba Winnipeg, Manitoba, Canada References 1. Monro D: The Anatomy of the Humor, Bones and Nerves. Edinburgh: Hamilton & Balfour, 1746, p 363 2. Parkinson D: Collateral circulation of cavernous carotid artery: anatomy. Can J Sorg 7:251-268, 1964 3. Parkinson D, Ramsay R: Carotid cavernous fistula with pulsating exophthalmus: a fortuitous cure. Can J Surg 6: 191-195, 1963 4. Pernkopf E: Atlas of Topographic and Applied Human Anatomy, Vol 1. Philadelphia: WB Saunders, 1963, pp 65, 73, 75 5. Williams PL, Warwick R: Gray's Anatomy, ed 6. Edinburgh: Churchill Livingstone, 1980, p 747 6. Winslow JB: Exposition Anatomique de la Structure du Corps Humain, Vol 2. London: Prevast, 1734, p 31

RESPONSE: The authors are honored by Dr. Parkinson's interest and comments pertaining to our cover illustration. The cast of the cavernous sinus was presented to one of the authors (J.T.K.) by Dr. Frederick Deuschle, one of Dr. Batson's students. Dr. Deuschle provided this cast in response to a query regarding the mechanism of formation of a carotid cavernous fistula. While Dr. Batson focused considerable attention on the intra- and extraspinal venous anatomy that bears his name, Batson's venous plexus, to our knowledge he never published his observations on the cavernous sinus. On the other hand, this cast has served us well in developing an understanding of the parasellar region, an "anatomical jewel box. ''3 The venous bulk on the right carotid siphon represents the actual photograph of the cavernous sinus cast and was not altered by the artist. Perhaps the two-dimensional presentation of a three-dimensional structure accounts in part for this apparent increased vascularity. At the same time, the cast illustrates the interconnection of the left and right cavernous sinus areas by venous plexuses in the floor of what was the sella turcica as well as venous connec342

tions to the pterygoid plexus of the pterygoid fossa inferiorly. Dr. Parkinson is again absolutely correct because the artist has taken the liberty to illustrate the fourth nerve freed from its dural connection, therefore allowing it to bow inferiorly making Parkinson's triangle even more narrow than it is in situ. The authors would also make note that they deliberately selected to omit the sympathetic nerves in the cavernous sinus to avoid cluttering and potential confusion of this illustration. Furthermore, other investigations describing the presence of parasympathetic nerves in the cavernous sinus have not been illustrated in this or other surgical descriptions of the sinus, but may yet be of significance as we gain an understanding of their import.~'2'4 While Dr. Parkinson is correct that the first detailed anatomy of the cavernous sinus was published in his article of 1964 not 1963, we were convinced of Dr. Parkinson's understanding of this region in 1963 when he stated, "this collateral circulation has been studied further and will be discussed in a subsequent publication" - - thus the premature credit! JEFFREY T. KELLER, PH.D. HARRY R. VAN LOVEREN, M.D.

University of Cincinnati Medical Center Cincinnati, Ohio References

I. Chorobski J, Penfield W: Cerebral vasodilator nerves and their pathway from the medulla oblongata. With observations on the pial and intracerebral vascular plexus. Arch Neurol Psychiatry 28:1257-1289, 1932 2. Moskowitz MA: Cluster headache: evidence for a pathophysiologic focus in the superior peficarotid cavernous sinus plexus. Headache 28:584-586, 1988 3. Parkinson D: Carotid cavernous fistula. History and anatomy, in Dolenc VV (ed): The Cavernous Sinus. New York: Springer-Verlag, 1987, pp 3-29 4. Ruskell GL: The orbital branches of the pterygopalatine ganglion and their relationship with internal carotid nerve branches in primates. J Anat 106:323-339, 1970

Lateral Disc Herniations

To THE EDITOR: In a recent article, the authors reverted to the term "lateral discs" while describing extreme lateral disc herniations (Garrido E, Connaughton PN: Unilateral facetectomy approach for lateral lumbar disc herniation. J Neurosurg 74:754-756, May, 1991). Years ago the term "extreme lateral" disc herniation was coined to avoid confusion with "lateral discs." For decades, spine surgeons used the latter term to describe herniated discs, other than central, that compress the nerve root existing one level below. They used the term "far lateral" mostly in reference to extruded fragments that present posterior to the nerve root or extend underneath it toward the foramen below. On the other hand, "extreme lateral" was used as a descriptive term for herniations that compress the nerve J. Neurosurg. / Volume 76 / February, 1992