Neurosurgical forum tissue pressure in the scalp. In our simulation, therefore, bility of overdrainage from the foramen of Monro was we included this variable factor in different ranges to pro- unavoidable, as shown in the same figure (Fig. 7). duce unique correlation between the closing pressure of We therefore searched for a different implantation site, the valves and the flow performance. namely the mastoid process and clavicle. It has been sug- The authors’ assumption of the Delta chamber’s ability gested by Tokoro and Chiba3 that one implant the ASD to “diffuse” the pressure could in no way ensure the effi- valve 10 cm below the level of the foramen of Monro, but cacy of their valve in maintaining the closing pressure no such suggestion has been made for implantation of the uniformly in different head positions, as the diffuse hydro- Delta valve. Because of our familiarity with the less hos- static pressure on the valve has been established in rela- pitable subcutaneous environment in the mastoid region tion to the closing pressure change of the valves (Fig. 5 of and/or clavicle, we also examined the shunt flow charac- the article). teristics with variable external pressure (5Ð9 cm H2O) and We can address Dr. Pollay’s question regarding the suggested that the other two sites may be an alternative to application of the pressure transducer by repeating our prevent underdrainage in patients with normal-pressure previous explanation that it was placed by removing the hydrocephalus. At the same time we noted the variable Delta chamber (as shown in Fig. 1 of the article). There is subcutaneous pressure that can result in shunt malfunction no question of any geometric compromise as the figure at those sites. Therefore what the authors find disturbing reveals. It is interesting to note here that our selection of a is indeed the case: the unresolved need to establish an transducer with a raised ring around the sensor (see Fig. 1 optimum site for implantation of the Delta valve. of the article) is very similar to that of the Delta chamber; Finally, we wish to express our gratitude for giving us this strongly supports the observed result of a rise in sub- the opportunity to clarify the problems of siphon-reducing cutaneous pressure. devices in treating hydrocephalus, and would like to make Although the Delta valve differs from the design of the particular mention of our concern about implanting these antisiphon device (ASD) in regard to the inlet-to-outlet devices in patients with normal-pressure hydrocephalus. surface area (20:1 vs. 8:1) as the authors note in their let- MAHMOOD HASSAN, M.B.B.S. ter, the paper by Horton and Pollay2 mentions that the SOTARO HIGASHI, M.D. ASD and SCD were substantially equivalent in the per- JUNKOH YAMASHITA, M.D. formance characteristics and surgical implantation tech- Kanazawa University School of Medicine niques. We selected the Delta valve according to our clin- Kanazawa, Japan ical experience as we investigated the reason for the observed malfunction. It is obvious that the ASD would References show similar limitations. 1. da Silva MC, Drake JM: Effect of subcutaneous implantation of Correct interpretation of the graphs would definitely anti-siphon devices on CSF shunt function. Pediatr Neurosurg assist the operator in selecting a valve, and it is clear that 16:197Ð202, 1990 our results (Figs. 6 and 7 of the article) were obtained in a 2. Horton D, Pollay M: Fluid flow performance of a new siphon- simulation in which the effects of such variable factors control device for ventricular shunts. J Neurosurg 72: as abdominal back pressure in different head positions, 926Ð932, 1990 external pressure on the device, and variation of valve 3. Tokoro K, Chiba Y: Optimum position for an antisiphon de- implantation site on the valves with siphon-reducing vice in a cerebrospinal fluid shunt system. Neurosurgery 29: devices were taken into consideration. It should be repeat- 519Ð525, 1991 ed here that at first we determined the extent of the rise in subcutaneous pressure on the Delta valve implanted Microsurgical Anatomy of the Jugular Foramen in rats before applying the range of observed pressure TO THE EDITOR: We read with interest the article by change in the in vitro simulation model. Ayeni, et al. (Ayeni SA, Ohata K, Tanaka K, et al: The The ultimate goal of shunt placement in a patient with microsurgical anatomy of the jugular foramen. J Neuro- hydrocephalus should be to ensure performance of daily surg 83:903Ð909, November, 1995). They observed in life activities without invasive procedures. As our simula- one of their specimens a long extracranial extension of tion results have pointed out, valves with siphon-reducing the inferior petrosal sinus (IPS), which joined the internal properties have so far not succeeded in doing this. Al- jugular vein (IJV) at the level of the atlas (illustrated in though we found that the closing pressure of PL-1.5 and their Fig. 2). The authors named this extracranial segment -2 valves remains within the normal physiological range of the IPS “the inferior petrosal vein” (IPV), according to of intracranial pressure from all implantation sites (see Padget’s8 statement that the IPV was “the extracranial end Fig. 7 of the article) under variable external pressure, it of the sinus of the same name.” In other neurosurgical7 does not do so when the patient attains erect posture. and neuroradiological1 literature, however, IPV has been Without describing the head position of their patient, Dr. used to describe a vein that shares its origin in the ponto- Pollay and his colleague noted the efficacy of the PL-1 cerebellar region with the superior petrosal vein (or vein valve from their prescribed foramen of Monro level, and of Dandy), but rejoins the inferior instead of the superior that the PL-1 Delta valve ensures sufficient flow equal to petrosal sinus. the CSF formation rate. In our simulation we showed that In anatomical specimens and more frequently during the same valve would cause underdrainage in the erect routine cerebral digital subtraction angiography (Fig. 1), position, as its closing pressure attains nonphysiological we have observed, as did Ayeni, et al., an inferior ex- levels with greater than 5 cm H2O pressure on the Delta tracranial venous extension of the IPS, which may be sev- chamber; however, when in the supine position the possi- eral centimeters in length and exhibit sizes matching the

J. Neurosurg. / Volume 85 / December, 1996 1193 Neurosurgical forum

RESPONSE: We thank Dr. Gailloud and colleagues for their comments on our paper. Matsushima, et al.,3 state that “the petrosal veins are divided into superior and infe- rior petrosal veins based on whether they enter the superi- or or inferior petrosal sinus,” and add that “the inferior petrosal veins are represented by a few small bridging veins.” According to Braun and Tournade,1 each vein of the lateral recess of the fourth ventricle terminates by becoming the direct or indirect affluent of the superior or inferior petrosal veins. On the left side of Fig. 1 in the arti- cle by Braun and Tournade,1 they show the vein of the lat- eral recess of the fourth ventricle draining into the lateral bulbopontine vein, which eventually drains into the supe- rior petrosal vein; on the right side, however, the vein of the lateral recess of the fourth ventricle joins the vein of the great sulcus of Vicq d’Azyr to form the “inferior pe- trosal vein.” Padget’s monumental work5 showed that the inferior petrosal sinus (IPS), unlike the internal jugular vein (IJV), which develops from the anterior cardinal vein, is a sec- ondary sinus developing from the prootic sinus which is the primary stem from the middle dural plexus. It is also FIG. 1. Venous phase of a left carotid angiogram showing an common knowledge that “fundamentally, in all species, extracranial extension of the inferior petrosal sinus (arrowheads) the superior petrosal sinus is the major metencephalic vein paralleling the inferior jugular vein. of the posterior fossa;”5 however, “seldom at birth do the cavernous sinus and the inferior petrosal sinus drain any veins of the brain.”4 According to Lang,2 the pons pos- sesses a venous network that is extremely variable in its caliber of the IJV.4 This anatomical variant has rarely been 2,5,6 arrangement and drainage. Although he states that “there described in the anatomical literature. However, to are veins which run through the subarachnoid space into avoid double use of the term IPV, we propose to name this the inferior petrosal sinus, to the area of the jugular fora- venous extension of the IPS “accessory internal jugular 3 men and to the venous plexus of the hypoglossal canal,” vein,” because it parallels the IJV in a close topographic he does not use the term “inferior petrosal veins” for the relation. vein(s) that run(s) to the inferior petrosal sinus. We be- PHILIPPE GAILLOUD, M.D. lieve that as a logical consequence of development and JEAN H. D. FASEL, M.D. MICHEL MUSTER, R.T. draining patterns, those veins described as inferior petros- 3 1 MICHEL PIOTIN, M.D. al veins by Matsushima, et al., and Braun and Tournade DANIEL A. RU¬ FENACHT, M.D. should simply be called bridging veins. The term inferior University of Geneva petrosal vein should be reserved for the extracranial end of Geneva, Switzerland the sinus of the same name that drains into the IJV, as was shown in Fig. 2 of our paper. Also, it would be incorrect References to use the term “accessory internal jugular vein” to describe the extracranial end of the IPS draining into the 1. Braun JP, Tournade A: The veins of the lateral recess of the 4th IJV because the IJV and IPS have different developmen- ventricle. Neuroradiology 7:9Ð13, 1974 2. Charpy A, Hovelacque A: Veines en particulier, in Nicolas A tal origins and their drainage patterns in the embryo, fetus, (ed): Traité d’Anatomie Humaine de Poirier et Charpy, ed and newborn are very different. 3. Paris: Masson, 1920, Vol 2, Fasc 3, pp 53Ð278 S. ADETOKUNBOH AYENI, M.D. 3. Fasel JHD, Gailloud P, Muster M, et al: The accessory internal Washington Hospital Center jugular vein in neuroradiologic catheterizations of the inferior Washington, D.C. petrosal sinus. Surg Radiol Anat 17:211, 1995 (Abstract) KEINJI OHATA, M.D. 4. Gailloud P, Fasel JHD, Muster M, et al: Termination of the infe- AKIRA HAKUBA, M.D. rior petrosal sinus: an anatomical variant. Clin Anat (In press, Osaka City University Medical School 1996) Osaka, Japan 5. Knott JF: On the cerebral sinuses and their variations. J Anat Physiol 16:27Ð42, 1882 References 6. Labalette F: Les Veines de la Tête et du Cou (Système de la Veine-Cave Supérieure). Applications Physiologiques et 1. Braun JP, Tournade A: The veins of the lateral recess of the 4th Medico-Chirurgicales. Thesis. Lille: L. Daniel, 1891, pp 1Ð91 ventricle. Neuroradiology 7:9Ð13, 1974 7. Matsushima T, Rhoton AL Jr, de Oliveira E, et al: Micro- 2. Lang J: Clinical Anatomy of the Head. Neurocranium, Or- surgical anatomy of the veins of the posterior fossa. J Neuro- bit, Craniocervical Regions. Berlin: Springer-Verlag, 1983, surg 59:63Ð105, 1983 p 370 8. Padget DH: The cranial venous system in man in reference to 3. Matsushima T, Rhoton AL Jr, de Oliveira E, et al: Micro- development, adult configuration, and relation to the arteries. surgical anatomy of the veins of the posterior fossa. J Neu- Am J Anat 98:307Ð355, 1956 rosurg 59:63Ð105, 1983

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