Common surgical pitfalls in the skull

Technique

Common Surgical Pitfalls in the Skull Semih Keskil, M.D., Ph.D.,* Rabet Go ¨ zil, Ph.D.,† and Engin C¸algu ¨ ner, Ph.D.† *Department of Neurosurgery, Kırıkkale University School of Medicine, Kırıkkale, Turkey; †Department of Anatomy, Gazi University School of Medicine, Bes¸evler, Ankara, Turkey

Keskil S, Go ¨ zil R, C¸algu ¨ ner E. Common surgical pitfalls in the skull. Surg Neurol 2003;59:228 –31. BACKGROUND

A detailed knowledge of the morphologic variations in the ossicles, foramina, and ridges of the skull vault and skull base is vital to performing safe radical surgery. METHODS

A surgical reminder of possible pitfalls was composed based on the incidences of most of the minor variations such as the supraorbital notch, frontal foramen, metopism, foramen caecum, parietal foramina, bony defects in the fossa occipitalis cerebellaris, Inca bone, foramen lacerum anterius, incomplete posterolateral wall of the foramen ovale, absence of the medial or posterior wall of the foramen spinosum, foramen innominatus, foramen meningoorbitale, bony dehiscence of the internal carotid canal, bony ridge or torus in the floor of the external auditory meatus, foramen of Huschke, precondylar tubercle, foramen hypoglossi, anterior condylar canal, hypoglossal bridging, divided articular surface of the occipital condyle, high jugular bulb, paramastoid process, atlantooccipital assimilation, ossicle of Kerkring, delta or keyhole shaped bony defects in the anterior border of foramen magnum, foramen of Vesalius, posterior condylar canal, mastoid emissary foramen and occipital foramen in 200 skulls. CONCLUSION

Recognition of these structures and their possible variations will help in distinguishing normal from potentially abnormal structures during computed tomography and magnetic resonance imaging examinations, and in avoiding misinterpretations that lead to confusion during surgical interventions. Instrumentation near potential bone gaps may traumatize important neural or vascular structures. © 2003 Elsevier Science Inc.

for many decades, who treated them in a purely descriptive manner [6,9,15,16]. Most of the variants can seldom be categorized as abnormal—in fact, some of them are so common that it may be difficult to decide what is the ‘normal’ condition. Despite this, they tend to be neglected by clinicians and most of them are only mentioned in anatomic textbooks, being described in terms such as “rare” or “occasional.” Knowing the topographical anatomy of the skull structures in three planes and their morphometric values is necessary but not enough for a safe surgery; detailed knowledge of the morphologic variations is also vital. Along the cranium and skull base, there are numerous openings through which vital neural and vascular structures pass. Many variants of these foramina have been thoroughly described in the early anatomic and radiologic literature. Recognition of these variants is important not only for understanding the complex regional neurovascular anatomy but also for distinguishing normal from potentially abnormal structures. Misinterpretation of such variations has occasionally led to confusion during surgical interventions. There may be some bone gaps around such foramina and instrumentation near these areas may traumatize important neural or vascular structures. Our aim was to compose a surgical reminder based on our previous works [7,12,13].

KEY WORDS

Skull base, foramen, variation, neurosurgery, anatomy.

inor variations in the ossicles, foramina, and ridges of the cranium have attracted the interest of anatomists and physical anthropologists

M

Address reprint requests to: Dr. Semih Keskil, Fethiye Sokak No: 4/6, Gazi Osman Pasខ a, 06700 Ankara, Turkey. Received October 2, 2001; accepted August 16, 2002. 0090-3019/03/$–see front matter doi:10.1016/S0090-3019(02)01038-8

Materials and Methods The material examined included 200 human skulls from the collections of Gazi University School of Medicine, Department of Anatomy, and Ankara University, Faculty of Letters, Department of Physical Anthropology. Data from males and females have been combined as it is known that there are no sex differences in the incidences of variations [5,6]. On the average, every one of the skulls examined pos© 2003 by Elsevier Science Inc. 360 Park Avenue South, New York, NY 10010 –1710

Skull Pitfalls

sessed two or three different variants. It was impossible to examine some of the variants published in the literature (such as presence or absence of the styloid process) because of the condition of the skulls we used. Thus, incidences for some variants are indicated in parentheses. FINDINGS The supraorbital foramen through which the supraorbital vessel and nerve pass is frequently incomplete and described as the “supraorbital notch (61%).” A secondary foramen in its vicinity (usually lateral to it), the “foramen (supratrochlearis) frontalis (16%)” may be in the form of a cluster of bony foramina. Although the mediofrontal suture disappears within the first 2 years of life, it may occasionally persist throughout life, this condition being known as “metopism (9%)” [5,6,9,17]. The “foramen caecum” may occasionally be patent and traversed by a vein joining the superior sagittal sinus with the veins of the nose [23]. The “foramen parietalis (63%)” is in some cases markedly enlarged, admitting a finger tip. It is more commonly unilateral (31%) than bilateral (27%); rarely, it is multiple, or accompanied by or replaced by a single median (sagittal) foramen (5%) [21,22,31]. The occipital bone is also occasionally paper-thin and even in the form of a “fossa occipitalis cerebellaris bone defect (0.5%).” In some cases, the pars interparietalis of the occipital bone does not fuse to the squama at the sutura mediosa before birth and remains separate as an “Inca bone (7.5%)” [23]. Lack of a bony spur from the greater wing to the lateral aspect of the sphenoid bone that separates the foramen rotundum from the superior orbital fissure result in “foramen lacerum anterius” [11]. Rarely, because of the “incomplete posterolateral wall of the foramen ovale (0.75%)”, the foramen ovale is continuous with the foramen spinosum [5,6,9,17]. The foramen spinosum may also exhibit varying degrees of incomplete formation, ranging from a small notch or groove in the greater wing of the sphenoid bone to an “absent medial or posterior wall” [5,6,9,17]. A “foramen innominatus (12%)” is occasionally located on the medial part of the foramen spinosum or between the foramen ovale and foramen spinosum. In some cases, there is a “foramen meningoorbitale (21%)” that extends from the fossa cranii media to the outer wall of the orbita [30]. One of the important variations that occurs in the temporal bone is the presence of a “bony dehiscence of the internal carotid canal” [7,20], defined as a definite lack of continuity of the bony coverage.

Surg Neurol 229 2003;59:228 –31

Rarely, a “bony ridge or torus in the floor of the external auditory meatus” [5] may be present, or occasionally there is a foramen in its place, the “foramen of Huschke (21%).” Such a foramen is always present in young children but only occasionally persists after the fifth year [5,6,9,16,17]. Occasionally one or two bony tubercles lie immediately anterior and medial to the occipital condyle [5,6,9,17], called the “precondylar tubercle (3.5%).” As the hypoglossal nerve originates from several segments embryologically, the “foramen hypoglossi or anterior condylar canal” may have many patterns: no trace of division (78%); one osseous spur (spine) located either marginally at the inner or outer orifice of the canal or inside it (4%); two or more osseous spurs located anywhere along the canal (2%); complete osseous bridging either in the internal or external part of the canal (13%); or complete osseous “hypoglossal bridging (3%)” extending along the whole canal [5,6,9,14,17]. Occasionally the “divided articular surface of the occipital condyle (1%)” is in the form of two distinct facets, sometimes called the third condyle [5,6,9,17]. The common finding that the jugular bulb is higher on the right side and its lack of any correlation with the mastoid size must be kept in mind while performing surgery through the temporal bone [3,4,25,26], because a “high jugular bulb” obstructs the surgeon’s view. The inferior surface of the jugulare process may be roughened by attachment of the rectus capitis lateralis in the form of a “paramastoid process,” projecting down and even articulating with the atlantal transverse process. Laterally, the jugular process may have a rough quadrilateral or triangular area joined to the jugular surface of the temporal bone by a growth plate of cartilage, which begins to ossify at about 25 years [6,9]. “Atlanto-occipital assimilation (1%)”—also called occipitalization—is known to be unilateral in some cases [8,27,28,29]. Occasionally an “ossicle of Kerkring” may occur at the posterior rim of the foramen magnum. It may either fuse into the squama or persist into adulthood [23,24]. There is also an occasional “delta shaped foramen magnum (17.5%)” or “keyhole shaped bone defect in the anterior border of the foramen magnum” [18,19]. In regard to the emissary veins, their role is limited when the normal routes of venous drainage are patent. However, when venous outflow is compromised (i.e., jugular thrombosis); they become alternative pathways for venous drainage of the brain. Recognition of these structures and their possible enlargement into pathologically large emissary veins— even in the form of bone defects—will help

230 Surg Neurol 2003;59:228 –31

avoid misinterpretations during computed tomography or magnetic resonance imaging examination. In neurosurgical approaches performed in the sitting position, there is a major risk of fatal air embolism because of the negative pressure in scalp veins if the surgeon erroneously lacerates these emissary veins [1,2,23]. On the medial part of the foramen ovale, there is an occasionally “foramen of Vesalius (8.5%)” [30] which opens into the lateral part of the fossa scaphoidea. The “posterior condylar canal (40%),” which pierces the condylar fossa immediately posterior to the occipital condyle sometimes transmits an emissary vein which allows anastomosis of the jugular bulb or sigmoid sinus to the suboccipital venous plexus [5,6,9,10,17]. There is also a “mastoid emissary foramen (78.5%)” (in the suture line in 88.5% of cases) that is larger and often multiple on the right side [23]. On the squamous portion of the occipital bone just posterior to the rim of the foramen magnum [12] there is the “occipital foramen (2.6%),” the inner opening of which is close to the inferior rim of the internal occipital protuberance; the vein that passes through it connects the confluence of sinuses and occipital vein. We would like to thank Professor Erksin Gulec¸ , PhD, for allowing us to examine the skulls in the collection of Department of Physical Anthropology, Ankara University Faculty of Letters.

REFERENCES 1. Albin MS, Babinski M, Maroon JC, Jannetta PJ. Anesthetic management of posterior fossa surgery in the sitting position. Acta Anesth Scand 1976;20:117–28. 2. Alexander EJR. Neurosurgical techniques. J Neurosurg 1966;24:818 –9. 3. Aristegui M, Cokkeser Y, Saleh E, et al. Retrolabyrinthine vestibular neurectomy. In: Filipo R, Barbara M, eds. Meniere’s Disease: Perspectives in 90’s. Amsterdam: Kugler Publications 1994:557–60. 4. Aslan A, Falcioni M, Russo A, et al. Anatomical considerations of high jugular bulb in lateral skull base surgery. J Laryngol Otol 1997;111:333–6. 5. Berry AC, Berry RJ. Epigenetic variation in the human cranium. J Anat 1967;101:361–79. 6. Berry AC. Factors affecting the incidence of nonmetrical skeletal variants. J Anat 1975;120:519 –35. 7. C¸ algu ¨ ner E, Turgut HB, Go ¨ zil R, Tunc¸ E, Sevim A, Keskil S. Measurements of the carotid canal in skulls from central Anatolia. Acta Anatomica 1997;158: 130 –2. 8. Chopra JS, Sawhney IM, Kak VK, Khosla VK. Craniovertebral anomalies: a study of 82 cases. Br J Neurosurg 1988;2:455–64. 9. Corruccini RS. An examination of the meaning of cranial discrete traits for human skeletal biological studies. Am J Phys Anthrop 1974;40:425–46.

Keskil et al

10. Ginsberg LE. The posterior condylar canal. Am J Neuroradiol 1994;15:969 –72. 11. Ginsberg LE, Pruett SW, Chen MYM, Elster AD. Skullbase foramina of the middle cranial fossa: reassessment of normal variation with high-resolution CT. Am J Neuroradiol 1994;15:283–91. 12. Go ¨ zil R, Kadiog˘ lu D, C¸ algu ¨ ner E. Occipital emissary foramen in skulls from Central Anatolia. Acta Anatomica 1995;153:325–6. 13. Go ¨ zil R, Keskil S, C¸ algu ¨ ner E, Tunc¸ E, Kadiog˘ lu D, ¨ nal B, Baykaner K. Neurocranial morpholSevim A, O ogy as determined by asymmetries of the skull base. J Anat 1996;189:673–5. 14. Hauser G, De Stefano GF. Variations in form of the hypoglossal canal. Am J Physical Anthropol 1985;67: 7–11. 15. Hauser G, De Stefano GF. Epigenetic variants of the human skull. E. Schweizerbart’sche Verlagbuchhandlung. Stuttgart: No ¨ gele U. Obermiller, 1989. 16. Herzog S, Fiese R. Persistent foramen of Huschke: possible risk factor for otologic complications after arthroscopy of the temporomandibular joint. Oral Surg Oral Med Oral Pathol 1989;68:267–70. 17. Kellock WL, Parsons PA. Variation of minor nonmetrical cranial variants in Australian Aborigines. Am J Phys Anthrop 1970;32:409 –22. 18. Lang J, Schafhauser O, Hoffmann S. Postnatal development of transbasal skull openings: carotid canal, Jugular foramen, hypoglossal canal, condylar canal and foramen magnum. Anat Anz 1983;153:315–57. 19. Martin R, Saller K. Lehrbuch der Anthropologie. Stuttgart: Gustav Fischer Verlag, 1957:1–50. 20. Moreano EH, Paparella MM, Zelterman D, Goycoolea MV. Prevalence of carotid canal dehiscence in the human middle ear: a report of 1000 temporal bones. Laryngoscope 1994;104:612–8. 21. O’Rahilly R, Twohig MJ. Foramina parietalia permagna. Am J Roentgen 1952;67:551–61. 22. Pendergrass EP, Pepper OHP. Observations on the process of ossification in the formation of persistent enlarged parietal foramina. Am J Roentgenol 1939;41: 343–6. 23. Redfield A. A new aid to aging immature skeletons: development of the occipital bone. Am J Phys Anthrop 1970;33:207–20. 24. Robinson A. Cunningham’s textbook of anatomy, 5th edition. New York: William Wood and Company, 1925. 25. Saleh E, Aristegui M, Taibah AK, Mazzoni A, Sanna M. Management of the high jugular bulb in the translabyrinthine approach. Otolaryngol Head Neck Surg 1994; 110:397–9. 26. Sanna M, Saleh E, Russo A, Taibah AK. Atlas of temporal bone and lateral skull base surgery. Stuttgart: Thieme Medical Publishers, 1995:37–50. 27. Smoker WR. Craniovertebral junction: normal anatomy, craniometry and congenital anomalies. Radiographics 1994;14:255–77. 28. Taitz C. Bony observations of some morphological variations and anomalies of the craniovertebral region. Clin Anat 2000;13:354 –60. 29. To ¨ ro ¨ I, Szepe L. Untersuchungen u ¨ ber die Frage der assimilation und manifestation des Atlas. Z Anat Entwickl-Gesch 1942;3:186 –200. 30. Williams PL, Warwick R. Gray’s anatomy. 37th edition. London: Livingstone, 1989:374.

Skull Pitfalls

Surg Neurol 231 2003;59:228 –31

31. Young ID, Swiff PGF. Parietal foramina in the SaethreChotzen syndrome. J Med Genet 1985;22:413–4.

COMMENTARY

Keskil et al have investigated the variations of the skull in quite a large series. They have also clearly detailed many anatomical structures in this presentation, which should enable readers to easily understand the anatomy. Although there have been many separate studies of individual variations, the study by Keskil et al covers these variations in a

single paper, further contributing to its significance. Unlike many previous studies that present a large set of numbers, this paper’s simplicity and comprehensibility give it additional value. We believe it will be very useful to physicians interested in surgery in this area. Yu ¨ cel Kanpolat, M.D. Ibrahim Tekdemir, M.D. Department of Neurosurgery University of Ankara Ankara, Turkey

oncovered or Bust! From a letter to CMS: I received a form and your letter regarding HIPAA (Health Interference Plan Absolutely Awful) and want to let you know that I only do hard copy, not electronic transfer of information. I was the first plastic surgeon in Naples and have taken care of about 14,000 patients over 27 years, without a single complaint from patients about a violation of their privacy. I am basically a country doctor following in the footsteps of my great-grandfather, who practiced in rural KY in the 1900s. Companies trying to sell me HIPAA compliance programs are coming out of the woodwork. Current Medicare payments barely exceed overhead; Medicaid often doesn’t even do that. Forcing me to comply with HIPAA would cost well over $10,000, even more over time, which I am not prepared to pay. If forced to comply, I will probably quit. Christopher Mogelvang, M.D., Naples, FL

N

—AAPS News, December 2002