Highly Cited Works in Skull Base Neurosurgery

Education & Training

Highly Cited Works in Skull Base Neurosurgery Nickalus R. Khan1, Siang Liao Lee3, Matthew Brown1, Jonathan Reding1, Jonathan Angotti2, Jacob Lepard2, Kyle Gabrick2, Paul Klimo, Jr.1,4, L. Madison Michael II1,4

OBJECTIVE: Citation analysis can be used to evaluate an article’s impact on its discipline. This study characterizes the most-cited articles related to skull base surgery.

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METHODS: The 100 most-cited skull base neurosurgery articles in all journals were examined. A separate listing of the top 100 most-cited articles in dedicated skull base journals was also examined. The following information was recorded for each article: number of authors, country of origin, citation-count adjusted for number of years in print, topic, and level of evidence.

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RESULTS: The 100 overall most-cited articles appeared in 25 journals. The top 100 most-cited articles in dedicated skull base journals appeared in 3 journals. Publication dates ranged from 1965e2006 for the overall list and 1993e2010 for the dedicated skull base list. Citations ranged from 11e59 (mean, 19) for the dedicated skull base list and 115e487 for the overall list (mean, 175). The average time-adjusted citation count was 8.4 for the overall list and 2 for the dedicated skull base journal list.

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CONCLUSIONS: An original article in a nondedicated skull base journal related to the subspecialty of skull base with a citation count of 150 or more and time-adjusted citation count of 10 can be considered a high-impact publication. An original article in a dedicated skull base periodical having a total citation count of 20 or more and an average citation count of 2 per year or more can be considered a high impact publication.

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Key words - Articles - Citation analysis - Neurosurgery - Skull base Abbreviations and Acronyms OCEBM: Oxford Centre for Evidence-Based Medicine WOS: Web of Science

INTRODUCTION

W

ithin scientific and—more specifically—neurosurgical literature, it is understood that a small percentage of publications can have a disproportionately large effect on clinical decision-making and operative technique. Citation analysis is able to differentiate these higher impact publications from the more than 50 million scientific publications in existence as of 2009 (11). Eugene Garfield (6, 7) first used the citation count as a surrogate for impact with the premise that articles of greater value will generate further readership, discussion, and change, which leads to increased citation counts. Therefore, citationbased metrics, such as citation counts, the journal impact factor, h-index, and normalized citation index, can be used to identify high impact articles and journals. A number of studies have identified landmark articles within various specialties using citation analysis: anesthesiology (27), critical care (24), dermatology (3), emergency medicine (28), forensic science (12-14), ophthalmology (20), orthopedics (16), otolaryngology (5), pediatric surgery (1), plastic surgery (17, 37), urology (8, 26), and neurosurgery (15, 21, 22, 29). Wilkins (30-33) and Wilkins et al. (34, 35) published a series of articles presenting his personally selected neurosurgical classics in the Journal of Neurosurgery between 1962 and 1965, which was later published as a stand-alone text. Davis and Cunningham (2) evaluated the laboratory research publications by 39 of the first American neurosurgeons. Drs. Cushing and Penfield each wrote 3 of the 10 most-cited articles in this series. In 2010, Ponce and Lozano (21, 22) used citation index as a means of determining the top 100 most-cited articles in the neurosurgical literature, as well as compiling a list of articles that have been cited more than 400 times, which he termed citation classics; however, of the 100 articles listed, there were only 3 that were specific to the subspecialty of skull base neurosurgery: 1) Jannetta’s original description of arterial compression of the trigeminal nerve in

University, Chicago, Illinois; and 4Semmes-Murphey Neurologic & Spine Institute, Memphis, Tennessee, USA To whom correspondence should be addressed: L. Madison Michael, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2015) 83, 4:403-418. http://dx.doi.org/10.1016/j.wneu.2014.12.005 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2015 Elsevier Inc. All rights reserved.

From the 1Department of Neurosurgery and 2College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee; 3Feinberg School of Medicine, Northwestern

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EDUCATION & TRAINING

patients with trigeminal neuralgia (9); 2) the explanation of the etiology and definitive microsurgical treatment of hemifacial spasm by Jannetta et al. (10); and 3) the long-term follow-up of patients after total removal of craniopharyngioma by Yasargil et al, (36). After this lead, the neurosurgical subspecialties have begun to use citation analysis to provide a catalogue of landmark articles related to their subspecialty. In pediatric neurosurgery, a composite of landmark articles has recently been established. These articles were identified by overall and time-adjusted citation count, leading to the production of two lists: 1) a listing of landmark articles from within pediatric neurosurgical journals (29), and 2) a listing of landmark articles related to pediatric neurosurgery but not present within dedicated pediatric neurosurgical journals (15). This composite now catalogues the most influential articles within the pediatric neurosurgery community based on how frequently each is cited by the academic community. The goal of the present article is to characterize and present two lists: 1) the top 100 overall most-cited articles related to skull base surgery and 2) a list of the top 100 most-cited articles within dedicated skull base journals.

Table 1. List of Key Words Used in Web of Science Search to Identify Articles Related to the Field of Skull Base Surgery Not Published in Dedicated Skull Base Journals Key Words Used in WOS Search  (Cranial) schwannoma surgery  (Skull base) aneurysm  (Skull base) meningioma surgery  (Skull base) radiosurgery  Acoustic neuroma  Cavernoma  Cavernous angioma  Cerebrospinal fluid leak  Chondrosarcoma  Chordoma  Craniopharyngioma  Encephalocele  Endoscopic neurosurgery  Epidermoid tumor  Esthesioneuroblastoma surgery

METHODS

 Glomus tumor

Journal Identification A search was performed in November 2013 using Elsevier’s Scopus (http://www.scopus.com). The terms skull base and neurosurgery were queried using the Source Title function within Scopus. Journals that were related to skull base neurosurgery were identified. Journals that were not directly related to clinical skull base neurosurgery (i.e., related to basic science research) were excluded. A separate search was performed in June 2014 using Thomson Reuter’s Web of Science (WOS) to identify articles present in nondedicated skull base journals (i.e., New England Journal of Medicine, JAMA, Journal of Neurosurgery, Neurosurgery). This search was performed by using a set of key words related to skull base neurosurgery to query all journals indexed in Thomson Reuter’s WOS (23) (Table 1). Citation Analysis Overall top 100 Most-Cited Articles. A total of 25 journals were identified from the initial search in WOS using the key words in Table 1. Each key word search was searched and the results were sorted in descending order by citation count and exported into Microsoft Excel (Redmond, Washington, USA). The 25 separate searches were combined into one database with more than 50,000 records sorted by descending citation count. Articles not directly related to skull base surgery (i.e., laboratory investigations, tumor articles not related to surgery) were excluded. The top 100 articles from this list were then further characterized. An “adjusted” citation count or index was calculated for each article by dividing the total number of citations by the years since initial publication. This adjusted citation count can be viewed as the average number of citations that article has received each year since it was published.

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 Hemifacial spasm  Microvascular decompression  Nasopharyngeal angiofibroma  Paranasal sinus cancer  Pituitary adenoma  Pituitary surgery  Rathke cleft cyst  Trigeminal neuralgia surgery  Trigeminal schwannoma

Dedicated Skull Base Journals. A total of 3 journals were identified from the Scopus search: 1) Journal of Neurological Surgery: Part B; 2) Skull Base; and 3) Skull Base Surgery. These journals were then compiled into a single search within Scopus (4) and WOS (23). This search returned a list of all articles (n ¼ 2381) present from these journals in Scopus and (n ¼ 781) within WOS records. These articles from Scopus were then sorted in descending order based on citation count. The top 100 most-cited articles were extracted from this list for analysis in November 2013. An “adjusted” citation count or index was calculated for each article by dividing the total number of citations by the years since initial publication. This adjusted citation count can be viewed as the average number of citations that article has received each year since it was published. Data The following information was obtained from each article: number of authors, institution, country of origin, type of research (retrospective or prospective), topic (endoscopic: procedures including endoscopic removal of tumor; tumor:

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WORLD NEUROSURGERY 83 [4]: 403-418, APRIL 2015

Table 2. List of Top 100 Most Cited Journal Articles Related to Skull Base Surgery From all Journals

Rank

Rank Citations

Adjusted Adjusted Rank Citations

Class

Barker FG 2nd, Jannetta PJ, Bissonette DJ, Larkins MV, Jho HD: The long-term outcome of microvascular decompression for trigeminal neuralgia. N Engl J Med 334:1077-1083, 1996.

1

487

1

27.06

3

Kondziolka D, Lunsford LD, McLaughlin MR, Flickinger JC: Long-term outcomes after radiosurgery for acoustic neuromas.N Engl J Med 339:1426-1433, 1998.

2

388

2

24.25

3

Gardner G, Robertson JH: Hearing preservation in unilateral acoustic neuroma surgery. Ann Otol Rhinol Laryngol 97:55-66, 1988.

3

383

8

14.73

4

Jannetta PJ, Abbasy M, Maroon JC, Ramos FM, Albin MS: Etiology and definitive microsurgical treatment of hemifacial spasm. Operative techniques and results in 47 patients. J Neurosurg 47:321-328, 1977.

4

364

30

9.84

3

Samii M, Matthies C: Management of 1000 vestibular schwannomas (acoustic neuromas): surgical management and results with an emphasis on complications and how to avoid them. Neurosurgery 40:11-23; discussion 13-21, 1997.

5

301

4

17.71

3

Wilson CB, Dempsey LC: Transsphenoidal microsurgical removal of 250 pituitary adenomas. J Neurosurg 48:13-22, 1978.

6

286

40

7.94

3

Brada M, Ford D, Ashley S, Bliss JM, Crowley S, Mason M, Rajan B, Traish D: Risk of second brain tumor after conservative surgery and radiotherapy for pituitary adenoma. Br Med J 304:1343-1346, 1992.

7

278

17

12.64

3

Higinbotham NL, Phillips RF, Farr HW, Hustu HO: Chordoma. Thirty-five-year study at Memorial Hospital. Cancer 20:1841-1850, 1967.

8

277

66

5.89

4

De Camilli P, Macconi D, Spada A: Dopamine inhibits adenylate cyclase in human prolactin-secreting pituitary adenomas. Nature 278:252-254, 1979.

260

49

7.43

3

10

258

5

17.20

4

Chan RC, Thompson GB: Morbidity, mortality, and quality of life following surgery for intracranial meningiomas. A retrospective study in 257 cases. J Neurosurg 60:52-60, 1984.

11

244

38

8.13

3

Knosp E, Steiner E, Kitz K, Matula C: Pituitary adenomas with invasion of the cavernous sinus space: a magnetic resonance imaging classification compared with surgical findings. Neurosurgery 33:610-617, 1993.

11

244

21

11.62

Grading system

Rich TA, Schiller A, Suit HD, Mankin HJ: Clinical and pathologic review of 48 cases of chordoma. Cancer 56:182-187, 1985.

13

242

35

8.34

4

Ezzat S, Asa SL, Couldwell WT, Barr CE, Dodge WE, Vance ML, McCutcheon IE: The prevalence of pituitary adenomas: a systematic review. Cancer 101: 613-619, 2004.

14

239

3

23.90

3

Ebersold MJ, Quast LM, Laws ER Jr, Scheithauer B, Randall RV: Long-term results in transsphenoidal removal of nonfunctioning pituitary adenomas. J Neurosurg 64:713-719, 1986.

15

233

37

8.32

4

Thapar K, Kovacs K, Scheithauer BW, Stefaneanu L, Horvath E, Pernicone PJ, Murray D, Laws ER Jr: Proliferative activity and invasiveness among pituitary adenomas and carcinomas: an analysis using the MIB-1 antibody. Neurosurgery 38:99-106, 1996.

16

232

16

12.89

4

Pollock BE, Lunsford LD, Kondziolka D, Flickinger JC, Bissonette DJ, Kelsey SF, Jannetta PJ: Outcome analysis of acoustic neuroma management: a comparison of microsurgery and stereotactic radiosurgery. Neurosurgery 36:215-224, 1995.

17

229

20

12.05

3

Flickinger JC, Kondziolka D, Niranjan A, Lunsford LD: Results of acoustic neuroma radiosurgery: an analysis of 5 years’ experience using current methods. J Neurosurg 94:1-6, 2001.

18

222

6

17.08

3

Harris JR, Levene MB: Visual complications following irradiation for pituitary adenomas and craniopharyngiomas. Radiology 120:167-171, 1976.

19

211

71

5.55

4

Abosch A, Tyrrell JB, Lamborn KR, Hannegan LT, Applebury CB, Wilson CB: Transsphenoidal microsurgery for growth hormone-secreting pituitary adenomas: initial outcome and long-term results. J Clin Endocrinol Metab 83:3411-3418, 1998.

19

211

12

13.19

3

405

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9

McLaughlin MR, Jannetta PJ, Clyde BL, Subach BR, Comey CH, Resnick DK: Microvascular decompression of cranial nerves: lessons learned after 4400 operations. J Neurosurg 90:1-8, 1999.

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Rank Black PM, Zervas NT, Candia GL: Incidence and management of complications of transsphenoidal operation for pituitary adenomas. Neurosurgery 20:902-904, 1987.

Rank Citations 21

204

Adjusted Adjusted Rank Citations 47

7.56

Class 3

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Matson DD, Crigler JF: Management of craniopharyngioma in childhood. J Neurosurg 30:377-390, 1969.

22

201

84

4.47

3

Ross DA, Wilson CB: Results of transsphenoidal microsurgery for growth hormone-secreting pituitary adenoma in a series of 214 patients. J Neurosurg 68:854-867, 1988.

23

199

44

7.65

3

Prasad D, Steiner M, Steiner L: Gamma surgery for vestibular schwannoma. J Neurosurg 92:745-759, 2000.

24

197

10

14.07

3

Gormley WB, Sekhar LN, Wright DC, Kamerer D, Schessel D: Acoustic neuromas: results of current surgical management. Neurosurgery 41:50-58 [discussion 58-60], 1997.

25

193

23

11.35

3

Bunin GR, Surawicz TS, Witman PA, Preston-Martin S, Davis F, Bruner JM: The descriptive epidemiology of craniopharyngioma. J Neurosurg 89:547-551, 1998.

25

193

19

12.06

3

Austin-Seymour M, Munzenrider J, Goitein M, Verhey L, Urie M, Gentry R, Birnbaum S, Ruotolo D, McManus P, Skates S, Ojemann RG, Rosenberg A, Schiller A, Koehler A, Suit HD: Fractionated proton radiation therapy of chordoma and low-grade-chondrosarcoma of the base of the skull. J Neurosurg 70:13-17, 1989.

27

191

45

7.64

3

Brada M, Rajan B, Traish D, Ashley S, Holmes-Sellors PJ, Nussey S, Uttley D: The long-term efficacy of conservative surgery and radiotherapy in the control of pituitary adenomas. Clin Endocrinol (Oxf) 38:571-578, 1993.

28

190

33

9.05

3

Jankowski R, Auque J, Simon C, Marchal JC, Hepner H, Wayoff M: Endoscopic pituitary tumor surgery. Laryngoscope 102:198-202, 1992.

29

189

34

8.59

Technique

Pozzati E, Acciarri N, Tognetti F, Marliani F, Giangaspero F: Growth, subsequent bleeding, and de novo appearance of cerebral cavernous angiomas. Neurosurgery 38:662-669 [discussion 669-670], 1996.

30

186

28

10.33

3

Jannetta PJ: Observations on the etiology of trigeminal neuralgia, hemifacial spasm, acoustic nerve dysfunction and glosspharyngeal neuralgia. Definitive microsurgical treatment and results in 117 patients. Neurochirugia (Stuttg) 20:145-154, 1977.

31

184

75

4.97

4

Samii M, Ammirati M, Mahran A, Bini W, Sepehrnia A: Surgery of petroclival meningiomas: report of 24 cases. Neurosurgery 24:12-17, 1989.

32

183

51

7.32

4

Barker FG 2nd, Jannetta PJ, Bissonette DJ, Shields PT, Larkins MV, Jho HD: Microvascular decompression for hemifacial spasm. J Neurosurg 82:201-210, 1995.

33

179

31

9.42

3

Cappabianca P, Cavallo LM, Colao A, de Divitiis E: Surgical complications associated with the endoscopic endonasal transsphenoidal approach for pituitary adenomas. J Neurosurg 97:293-298, 2002.

34

177

7

14.75

4

Estrada J, Boronat M, Mielgo M, Magallon R, Millan I, Diez S, Lucas T, Barcelo B: The long-term outcome of pituitary irradiation after unsuccessful transsphenoidal surgery in Cushing’s disease. N Engl J Med 336:172-177, 1997.

35

176

27

10.35

3

Burchiel KJ, Clarke H, Haglund M, Loeser JD: Long-term efficacy of microvascular decompression in trigeminal neuralgia. J Neurosurg 69:35-38, 1988.

36

175

61

6.73

3

Mattox DE, Kennedy DW: Endoscopic management of cerebrospinal fluid leaks and cephaloceles. Laryngoscope 100:857-862, 1990.

37

174

52

7.25

4

Wiegand DA, Fickel V: Acoustic neuroma—the patient’s perspective: subjective assessment of symptoms, diagnosis, therapy, and outcome in 541 patients. Laryngoscope 99:179-187, 1989.

38

173

57

6.92

Survey

Cappabianca P, Alfieri A, de Divitiis E: Endoscopic endonasal transsphenoidal approach to the sella: towards functional endoscopic pituitary surgery (FEPS). Minim Invasive Neurosurg 41:66-73, 1998.

39

171

25

10.69

Technique

Rajan B, Ashley S, Gorman C, Jose CC, Horwich A, Bloom HJ, Marsh H, Brada M: Craniopharyngioma—a long-term results following limited surgery and radiotherapy. Radiother Oncol 26:1-10, 1993.

40

166

41

7.90

3

EDUCATION & TRAINING

406

Table 2. Continued

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Table 2. Continued Rank

Rank Citations

Adjusted Adjusted Rank Citations

Class

407

41

165

73

5.16

4

Selman WR, Laws ER Jr, Scheithauer BW, Carpenter SM: The occurrence of dural invasion in pituitary adenomas. J Neurosurg 64:402-407, 1986.

41

165

67

5.89

4

Tsang RW, Laperriere NJ, Simpson WJ, Brierley J, Panzarella T, Smyth HS: Glioma arising after radiation therapy for pituitary adenoma. A report of four patients and estimation of risk. Cancer 72:2227-2233, 1993.

43

164

43

7.81

3

Yasargil MG, Abernathey CD, Sarioglu AC: Microneurosurgical treatment of intracranial dermoid and epidermoid tumors. Neurosurgery 24:561-567, 1989.

44

163

63

6.52

3

Catton C, O’Sullivan B, Bell R, Laperriere N, Cummings B, Fornasier V, Wunder J: Chordoma: long-term follow-up after radical photo irradiation. Radiother Oncol 41:67-62, 1996.

44

163

32

9.06

3

Van Effenterre R, Boch AL: Craniopharyngioma in adults and children: a study of 122 surgical cases. J Neurosurg 97:3-11, 2002.

46

161

11

13.42

3

Thomsett MJ, Conte FA, Kaplan SL, Grumbach MM: Endocrine and neurologic outcome in childhood craniopharyngioma: review of effect of treatment in 42 patients. J Pediatr 97:728-735, 1980.

47

160

80

4.71

3

Mohr G, Hardy J: Hemorrhage, necrosis, and apoplexy in pituitary adenomas. Surg Neurol 18:181-189, 1982.

48

159

76

4.97

4

Comtois R, Beauregard H, Somma M, Serri O, Aris-Jilwan N, Hardy J: The clinical and endocrine outcome to trans-sphenoidal microsurgery of nonsecreting pituitary adenomas. Cancer 68:860-866, 1991.

48

159

58

6.91

3

Morita A, Coffey RJ, Foote RL, Schiff D, Gorman D: Risk of injury to cranial nerves after gamma knife radiosurgery for skull base meningiomas: experience in 88 patients. J Neurosurg 90:42-49, 1999.

50

158

26

10.53

3

Glasscock ME 3rd, Hays JW, Minor LB, Haynes DS, Carrasco VN: Preservation of hearing in surgery for acoustic neuromas. J Neurosurg 78:864-870, 1993.

51

156

49

7.43

3

Kanter WR, Eldridge R, Fabricant R, Allen JC, Koerber T: Central neurofibromatosis with bilateral acoustic neuroma: genetic, clinical and biochemical distinctions from peripheral neurofibromatosis. Neurology 30:851-859, 1980.

52

153

83

4.50

3

Cummings BJ, Hodson DI, Bush RS: Chordoma: the results of megavoltage radiation therapy. Int J Radiat Oncol Biol Phys 9:633-642, 1983.

52

153

77

4.94

4

Hoffman HJ, Hendrick EB, Humphreys RP, Buncic JR, Armstrong DL, Jenkin RD: Management of craniopharyngioma in children. J Neurosurg 47:218-227, 1977.

54

151

91

4.08

3

Stevenson GC, Stoney RJ, Perkins RK, Adams JE: A transcervical transclival approach to the ventral surface of the brain stem for removal of a clivus chordoma. J Neurosurg 24:544-551, 1966.

55

150

95

3.13

4

De Vile CJ, Grant DB, Kendall BE, Neville BG, Stanhope R, Watkins KE, Hayward RD: Management of childhood craniopharyngioma: can the morbidity of radical surgery be predicted? J Neurosurg 85:73-81, 1996.

55

150

36

8.33

3

Folpe AL, Fanburg-Smith JC, Miettinen M, Weiss SW: Atypical and malignant glomus tumors: analysis of 52 cases, with a proposal for the reclassification of glomus tumors. Am J Surg Pathol 25:1-12, 2001.

55

150

22

11.54

3

Merchant TE, Kiehna EN, Sanford RA, Mulhern RK, Thompson SJ, Wilson MW, Lusting RH, Kun LE: Craniopharyngioma: the St. Jude Children’s Research Hospital experience 1984-2001. Int J Radiat Oncol Biol Phys 53:533-542, 2002.

55

150

18

12.50

4

Hetelekidis S, Barnes PD, Tao ML, Fischer EG, Schneider L, Scott RM, Tarbell NJ: 20-year experience in childhood craniopharyngioma. Int J Radiat Oncol Biol Phys 27:189-195, 1993.

59

149

55

7.10

4

Nadol JB Jr, Chiong CM, Ojemann RG, McKenna MJ, Martuza RL, Montgomery WW, Levine RA, Ronner SF, Glynn RJ: Preservation of hearing and facial nerve function in resection of acoustic neuroma. Laryngoscope 102:1153-1158, 1992.

60

146

62

6.64

3

Currau RL, Joh HD, Ko Y: Transnasal-transsphenoidal endoscopic surgery of the pituitary gland. Laryngoscope 106:914-918, 1996.

60

146

39

8.11

Technique Continues

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Suit HD, Goitein M, Munzenrider J, Verhey L, Davis KR, Koehler A, Linggood R, Ojemann RG: Definitive radiation therapy for chordoma and chondrosarcoma of base of skull and cervical spine. J Neurosurg 56:377-385, 1982.

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Rank

Rank Citations

Adjusted Adjusted Rank Citations

Class

Bederson JB, Wilson CB: Evaluation of microvascular decompression and partial sensory rhizotomy in 252 cases of trigeminal neuralgia. J Neurosurg 71:359-367, 1989.

62

145

69

5.80

3

Kruetzer J, Vance ML, Lopes MB, Laws ER Jr: Surgical management of GH-secreting pituitary adenomas: an outcome study using modern remission criteria. J Clin Endocrinol Metab 86:4072-4077, 2001.

63

144

24

11.08

4

Barker FG 2nd, Kilbanski A, Swearingen B: Transsphenoidal surgery for pituitary tumors in the United States, 1996-2000: mortality, morbidity, and the effects of hospital and surgeon volume. J Clin Endocrinol Metab 88:4709-4719, 2003.

63

144

13

13.09

3

Ojemann RG, Levine RA, Montgomery WM, McGaffigan P: Use of intraoperative auditory evoked potentials to preserve hearing in unilateral acoustic neuroma removal. J Neurosurg 61:938-948, 1984.

65

143

78

4.77

4

Zada G, Kelly DF, Cohan P, Wang C, Swerdloff R: Endonasal transsphenoidal approach for pituitary adenomas and other sellar lesions: an assessment of efficacy, safety, and patient impressions. J Neurosurg 98:350-358, 2003.

65

143

14

13.00

3

Hardy J, Wigser SM: Trans-sphenoidal surgery of pituitary fossa tumors with televised radiofluoroscopic control. J Neurosurg 23:612-619, 1965.

67

142

96

2.90

4

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Laws ER Jr: Transsphenoidal microsurgery in the management of craniopharyngioma. J Neurosurg 52:661-666, 1980.

68

141

90

4.15

Bigos ST, Somma M, Rasio E, Eastman RC, Lanthier A, Johnston HH, Hardy J: Cushing’s disease: management by transsphenoidal pituitary microsurgery. J Clin Endocrinol Metab 50:348-354, 1980.

69

138

92

4.06

Review 4

Fisch U: Infratemporal fossa approach for glomus tumors of the temporal bone. Ann Otol Rhinol Laryngol 91:474-479, 1982.

70

137

87

4.28

Technique

Toglia JU, Netsky MG, Alexander E Jr: Epithelial (epidermoid) tumors of the cranium. Their common nature and pathogenesis. J Neurosurg 23:384-393, 1965.

71

134

97

2.73

4

Yamakawa K, Shitara N, Genka S, Manak S, Takakura K: Clinical course and surgical prognosis of 33 cases of intracranial epidermoid tumors. Neurosurgery 24:568-573, 1989.

71

134

72

5.36

4

Cavazzuti V, Fischer EG, Welch K, Belli JA, Winston KR: Neurological and psychophysiological sequelae following different treatments of craniopharyngioma in children. J Neurosurg 59:409-417, 1983.

73

133

86

4.29

4

Kondo A: Follow-up results of microvascular decompression in trigeminal neuralgia and hemifacial spasm. Neurosurgery 40:46-51 [discussion 51-2], 1997.

74

129

46

7.59

3

Lonn S, Ahlbom A, Hall P, Feychting M: Mobile phone use and the risk of acoustic neuroma. Epidemiology 15:653-659, 2004.

74

129

15

12.90

3

Moller AR, Jannetta PJ: Preservation of facial function during removal of acoustic neuromas. Use of monopolar constant-voltage stimulation and EMG. J Neurosurg 61:757-760, 1984.

76

127

89

4.23

Technique

Nadol JB Jr, Levine R, Ojemann RG, Martuza RL, Montgomery WW, de Sandoval PK: Preservation of hearing in surgical removal of acoustic neuromas of the internal auditory canal and cerebellar pontine angle. Laryngoscope 97:1287-1294, 1987.

76

127

81

4.70

3

Tsang RW, Brierley JD, Panzarella T, Gospodarowicz MK, Sutcliffe SB, Smpson WJ: Radiation therapy for pituitary adenoma: treatment outcome and prognostic factors. Int J Radiat Oncol Biol Phys 30:557-565, 1994.

78

125

65

6.25

3

Thapar K, Scheithauer BW, Kovacs K, Pernicone PJ, Laws ER Jr: p53 expression in pituitary adenomas and carcinomas: correlation with invasiveness and tumor growth fractions. Neurosurgery 38:765-770 [discussion 770-771], 1996.

78

125

56

6.94

3

Wang A, Jankovic J: Hemifacial spasm: clinical findings and treatment. Muscle Nerve 21:1740-1747, 1998.

78

125

42

7.81

3

Tsuneyoshi M, Enjoji M: Glomus tumor: a clinicopathologic and electron microscopic study. Cancer 50:1601-1607, 1982.

81

124

94

3.88

4

Randall RV, Laws ER Jr, Abboud CF, Ebersold MJ, Kao PC, Scheithauer BW: Transsphenoidal microsurgical treatment of prolactin-producing pituitary adenomas. Results in 100 patients. Mayo Clin Proc 58:108-121, 1983.

82

123

93

3.97

3

EDUCATION & TRAINING

408

Table 2. Continued

WORLD NEUROSURGERY 83 [4]: 403-418, APRIL 2015

Table 2. Continued Rank

Rank Citations

Adjusted Adjusted Rank Citations

Class

83

122

85

4.36

Technique

Guilhaume B, Bertagna X, Thomsen M, Bricaire C, Vila-Porcile E, Oliver L, Racadot J, Derome P, Lauda MH, Girard F, Bricaire H, Luton JP: Transsphenoidal pituitary surgery for the treatment of Cushing’s disease: results in 64 patients and long term follow-up studies. J Clin Edocrinol Metab 66:1056-1064, 1988.

84

121

82

4.65

3

Foote RL, Coffey RJ, Swanson JW, Harner SG, Beatty CW, Kline RW, Stevens LN, Hu TC: Stereotactic radiosurgery using the gamma knife for acoustic neuromas. Int J Radiat Oncol Biol Phys 32:1153-1160, 1995.

84

121

64

6.37

4

McCord MW, Buatti JM, Fennell EM, Mendenhall WM, Marcus RB Jr, Rhoton AL, Grant MB, Friedman WA: Radiotherapy for pitutiary adenoma: long-term outcome and sequelae. Int J Radiat Oncol Biol Phys 39:437-444, 1997.

84

121

54

7.12

3

Waltz TA, Brownell B: Sarcoma: a possible latea result of effective radiation therapy for pitutiary adenoma. Report of two cases. J Neurosurg 24:901-907, 1966.

87

120

98

2.50

4

Hopf NJ, Perneczky A: Endoscopic neurosurgery and endoscope-assisted microneurosurgery for the treatment of intracranial cysts. Neurosurgery 43:1330-1336 [discussion 1336-1337], 1998.

87

120

48

7.50

4

Snyder PJ, Fowble BF, Schatz NJ, Savino PJ, Gennarelli TA: Hypopituitarism following radiation therapy of pituitary adenomas. Am J Med 81:457-462, 1986.

89

119

88

4.25

3

Knosp E, Kitz K, Perneczky A: Proliferation activity in pituitary adenomas: measurement by monoclonal antibody Ki-67. Neurosurgery 25:927-930, 1989.

89

119

79

4.76

3

Fahlbusch R, Schott W: Pterional surgery of meninigomas of the tuberculum sellae and planum sphenoidale: surgical results with special consideration of ophthalmological and endocrinological outcomes. J Neurosurg 96:235-243, 2002.

89

119

29

9.92

4

Bertalanffy H, Gilsbach JM, Eggert HR, Seeger W: Microsurgery of deep-seated cavernous angiomas: report of 26 cases. Acta Neurochir (Wien) 108:91-99, 1991.

92

118

74

5.13

4

Hsu DW, Hakim F, Biller BM, de la Monte S, Zervas NT, Klibanski A, Hedley-Whyte ET: Significance of proliferating cell nuclear antigen index in predicting pituitary adenoma recurrence. J Neurosurg 78:753-761, 1993.

93

117

70

5.57

4

Strasnick B, Glassock ME 3rd, Haynes D, McMenomey SO, Minor LB: The natural history of untreated acoustic neuromas. Laryngoscope 104:1115-1119, 1994.

93

117

68

5.85

3

Jho HD, Carrau RL, Ko Y, Daly MA: Endoscopic pitutiary surgery: an early experience. Surg Neurol 47:213-222 [discussion 222-223], 1997.

93

117

59

6.88

Technique

Klibanski A, Zervas NT: Seminars in medicine of the Beth Israel Hospital, Boston: diagnosis and management of hormone secreting pituitary adenomas. N Engl J Med 324:822-831, 1991.

96

116

60

6.82

Review

Mitsumori M, Shrieve DC, Alexander E 3rd, Kaiser UB, Richardson GE, Black PM, Loeffler JS: Initial clinical results of LINAC-based stereotactic radiosurgery and stereotactic radiotherapy for pituitary adenomas. Int J Radiat Oncol Biol Phys 42:573-580, 1998.

96

116

52

7.25

3

Samii M, Gerganov V, Samii A: Improved preservation of hearing and facial nerve function in vestibular schwannoma surgery via the retrosigmoid approach in a series of 200 patients. J Neurosurg 105:527-535, 2006.

96

116

9

14.50

4

Prass RL, Luders H: Acoustic (loudspeaker) facial electromyographic monitoring: Part 1. Evoked electromyographic activity during acoustic neuroma resection. Neurosurgery 19:392-400, 1986.

99

115

91

4.11

Technique

Yamasaki T, Handa H, Yamashita J, Paine JT, Tashiro Y, Uno A, Ishikawa M, Asato R: Intracranial and orbital cavernous angiomas. A review of 30 cases. J Neurosurg 64:197-208, 1986.

99

115

91

4.11

4

409

The first rank represents the descending rank order by raw citations. The second rank (i.e., Adjusted Rank) is based on the adjusted citation index (i.e., number of citations divided by years since initial publication). The column titled Class is the class of evidence for the article based on the 2011 Oxford Centre Level of Evidence classification scheme.

EDUCATION & TRAINING

www.WORLDNEUROSURGERY.org

Glasscock ME 3rd, Kveton JF, Jackson CG, Levine SC, McKennan KX: A systematic approach to the surgical management of acoustic neuroma. Laryngoscope 96:1088-1094, 1986.

410 Rank

Rank

Citations

Adjusted Rank

Adjusted Citations

Class

www.SCIENCEDIRECT.com

Snyderman CH, Kassam AB, Carrau R, Mintz A. Endoscopic Reconstruction of Cranial Base Defects following Endonasal Skull Base Surgery. Skull base: Official journal of North American Skull Base Society 17:73-78, 2007.

1

59

2

9.83

Technique

Deschler DG, Gutin PH, Mamelak AN, McDermott MW, Kaplan MJ: Complications of anterior skull base surgery. Skull Base Surg 6:113-118, 1996

2

50

22

2.94

4

Sanna M, Zini C, Gamoletti R, Frau N, Taibah AK, Russo A, Pasanisi E: Petrous bone cholesteatoma. Skull Base Surg 3:201-213, 1993.

3

44

39

2.20

4

Cappabianca P, Alfieri A, Colao A, Ferone D, Lombardi G, de Divitiis E: Endoscopic endonasal transsphenoidal approach: an additional reason in support of surgery in the management of pituitary lesions. Skull Base Surg 9:109-117, 1999.

4

43

20

3.07

4

WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.12.005

Smith ER, Scott RM: Surgical management of moyamoya syndrome. Skull Base 15:15-26, 2005.

5

39

5

4.88

Review

Matsushima T, Natori Y, Katsuta T, Ikezaki K, Fukui M, Rhoton AL: Microsurgical anatomy for lateral approaches to the foramen magnum with special reference to transcondylar fossa (supracondylar transjugular tubercle) approach. Skull Base Surg 8:119-125, 1998.

5

39

31

2.60

Technique

Gjuric M, Seidinger L, Wigand ME: Long-term results of surgery for temporal bone paraganglioma. Skull Base Surg 6:147-152, 1996.

7

32

46

1.88

4

George B, Lot G: Anterolateral and posterolateral approaches to the foramen magnum: technical description and experience from 97 cases. Skull Base Surg 5:9-19, 1995.

7

32

49

1.78

4

Pant H, Bhatki AM, Snyderman CH, Vescan AD, Carrau RL, Gardner P, Prevedello D, Kassam AB: Quality of life following endonasal skull base surgery. Skull Base 20:35-40, 2010.

9

31

1

10.33

4

Derdeyn CP, Grubb RL Jr, Powers WJ: Indications for cerebral revascularization for patients with atherosclerotic carotid occlusion. Skull Base 15:7-14, 2005.

10

30

15

3.75

Review

Castelnuovo PG, Delù G, Sberze F, Pistochini A, Cambria C, Battaglia P, Bignami M: Esthesioneuroblastoma: endonasal endoscopic treatment. Skull Base 16:25-30, 2006.

11

29

14

4.14

4

Liu JK, Burger PC, Harnsberger HR, Couldwell WT: Primary intraosseous skull base cavernous hemangioma: case report. Skull Base 13:219-228, 2003.

12

27

29

2.70

Case report

Behr R, Müller J, Shehata-Dieler W, Schlake HP, Helms J, Roosen K, Klug N, Hölper B, Lorens A: The high rate CIS auditory brainstem implant for restoration of hearing in NF-2 patients. Skull Base 17:91-107, 2007.

13

26

10

4.33

3

Gil Z, Abergel A, Leider-Trejo L, Khafif A, Margalit N, Amir A, Gur E, Fliss DM: A comprehensive algorithm for anterior skull base reconstruction after oncological resections. Skull Base 17:25-37, 2007.

13

26

10

4.33

4

Barami K, Hernandez VS, Diaz FG, Guthikonda M: Paraclinoid carotid aneurysms: surgical management, complications, and outcome based on a new classification scheme. Skull Base 13:31-41, 2003.

13

26

31

2.60

4

Kollert M, Minovi AA, Draf W, Bockmühl U: Cervical paragangliomas-tumor control and long-term functional results after surgery. Skull Base 16:185-191, 2006.

16

25

17

3.57

4

Zipfel GJ, Fox DJ Jr, Rivet DJ: Moyamoya disease in adults: the role of cerebral revascularization. Skull Base 15:27-41, 2005.

16

25

19

3.13

Review

Hamid O, El Fiky L, Hassan O, Kotb A, El Fiky S: Anatomic variations of the sphenoid sinus and their impact on trans-sphenoid pituitary surgery. Skull Base 18:9-15, 2008.

18

24

6

4.80

4

Biglioli F, Mortini P, Goisis M, Bardazzi A, Boari N: Submental orotracheal intubation: an alternative to tracheotomy in transfacial cranial base surgery. Skull Base 13:189-195, 2003.

18

24

34

2.40

4

Boedeker CC, Neumann HP, Offergeld C, Maier W, Falcioni M, Berlis A, Schipper J: Clinical features of paraganglioma syndromes. Skull Base 19:1725, 2009.

20

23

3

5.75

Review

Ceylan A, Köybas‚ioglu A, Celenk F, Yilmaz O, Uslu S: Surgical treatment of elongated styloid process: experience of 61 cases. Skull Base 18:289-295, 2008.

20

23

8

4.60

4

Quinones-Hinojosa A, Du R, Lawton MT: Revascularization with saphenous vein bypasses for complex intracranial aneurysms. Skull Base 15:119-132, 2005.

20

23

23

2.88

4

Kanaan I, Jallu A, Kanaan H: Management strategy for meningioma in pregnancy: a clinical study. Skull Base 13:197-203, 2003.

20

23

37

2.30

4

EDUCATION & TRAINING

Table 3. List of Top 100 Most Cited Journal Articles in Skull Base Neurosurgical Journals

WORLD NEUROSURGERY 83 [4]: 403-418, APRIL 2015

Table 3. Continued Rank

Citations

Adjusted Rank

Adjusted Citations

Class

Mazzoni A, Calabrese V, Moschini L: Residual and recurrent acoustic neuroma in hearing preservation procedures: neuroradiologic and surgical findings. Skull Base Surg 6:105-112, 1996.

20

23

60

1.35

4

Langer DJ, Vajkoczy P: ELANA: Excimer Laser-Assisted Nonocclusive Anastomosis for extracranial-to-intracranial and intracranial-to-intracranial bypass: a review. Skull Base 15:191-205, 2005.

25

22

28

2.75

Review

Wein RO, Popat SR, Doerr TD, Dutcher PO: Plasma cell tumors of the skull base: four case reports and literature review. Skull Base 12:77-86, 2002.

25

22

41

2.00

Review

Moe KS, Li D, Linder TE, Schmid S, Fisch U: An update on the surgical treatment of temporal bone paraganglioma. Skull Base Surg 9:185-194, 1999.

25

22

57

1.57

4

Ross DA, Marentette LJ, Moore CE, Switz KL: Craniofacial resection: decreased complication rate with a modified subcranial approach. Skull Base Surg 9:95-100, 1999.

25

22

57

1.57

4

El-Sayed IH, Roediger FC, Goldberg AN, Parsa AT, McDermott MW: Endoscopic reconstruction of skull base defects with the nasal septal flap. Skull Base 18:385-394, 2008.

29

21

13

4.20

4

Zweig JL, Carrau RL, Celin SE, Snyderman CH, Kassam A, Hegazy H: Endoscopic repair of acquired encephaloceles, meningoceles, and meningoencephaloceles: predictors of success. Skull Base 12:133-139, 2002.

29

21

44

1.91

4

Schmerber S, Righini C, Lavielle JP, Passagia JG, Reyt E: Endonasal endoscopic closure of cerebrospinal fluid rhinorrhea. Skull Base 11:47-58, 2001.

29

21

50

1.75

4

Tiwari R, Quak J, Egeler S, Smeele L, Waal IV, Valk PV, Leemans R: Tumors of the infratemporal fossa. Skull Base Surg 10:1-9, 2000.

29

21

56

1.62

4

Colletti V, Fiorino FG, Sacchetto L: Iatrogenic impairment of hearing during surgery for acoustic neuroma. Skull Base Surg 6:153-161, 1996.

29

21

63

1.24

Isolan GR, Rowe R, Al-Mefty O: Microanatomy and surgical approaches to the infratemporal fossa: an anaglyphic three-dimensional stereoscopic printing study. Skull Base 17:285-302, 2007.

34

20

18

3.33

Castelnuovo PG, Belli E, Bignami M, Battaglia P, Sberze F, Tomei G: Endoscopic nasal and anterior craniotomy resection for malignant nasoethmoid tumors involving the anterior skull base. Skull Base 16:15-18, 2006.

34

20

24

2.86

Rank

4 Technique 4

411

34

20

41

2.00

Fukushima T, Day JD, Hirahara K: Extradural total petrous apex resection with trigeminal translocation for improved exposure of the posterior cavernous sinus and petroclival region. Skull Base Surg 6:95-103, 1996.

34

20

65

1.18

Technique

4

Prescher A, Brors D, Adam G: Anatomic and radiologic appearance of several variants of the craniocervical junction. Skull Base Surg 6:83-94, 1996.

34

20

65

1.18

Technique

Ustuner Z, Basaran M, Kiris T, Bilgic B, Sencer S, Sakar B, Dizdar Y, Bavbek S, Onat H: Skull base plasmacytoma in a patient with light chain myeloma. Skull Base 13:167-171, 2003.

39

19

45

1.90

Case report

Nistor RF, Chiari FM, Maier H, Hehl K: The fixed combination of collagen with components of fibrin adhesive-a new hemostypic agent in skull base procedures. Skull Base Surg 7:23-30, 1997.

39

19

64

1.19

4

Schaller C, Rohde V, Hassler W. Microsurgical removal of olfactory groove meningiomas via the pterional approach. Skull Base Surg 4:189-192, 1994.

39

19

71

1.00

4

Huy PT, Kania R, Duet M, Dessard-Diana B, Mazeron JJ, Benhamed R: Evolving concepts in the management of jugular paraganglioma: a comparison of radiotherapy and surgery in 88 cases. Skull Base 19:83-91, 2009.

42

18

9

4.50

4

Ismail AS, Costantino PD, Sen C: Transnasal transsphenoidal endoscopic repair of csf leakage using multilayer acellular dermis. Skull Base 17:125-132, 2007.

42

18

21

3.00

4

Austin JR, Cebrun H, Kershisnik MM, El-Naggar AK, Garden AS, Demonte F, Ginsberg LE, Lippman SM, Goepfert H: Olfactory neuroblastoma and neuroendocrine carcinoma of the anterior skull base: treatment results at the m.d. Anderson cancer center. Skull Base Surg 6:1-8, 1996.

42

18

70

1.06

4

Pusic AL, Chen CM, Patel S, Cordeiro PG, Shah JP: Microvascular reconstruction of the skull base: a clinical approach to surgical defect classification and flap selection. Skull Base 17:5-15, 2007.

45

17

25

2.83

Technique

Continues

EDUCATION & TRAINING

www.WORLDNEUROSURGERY.org

Pareschi R, Righini S, Destito D, Raucci AF, Colombo S: Surgery of glomus jugulare tumors. Skull Base 13:149-157, 2003.

412 Rank

Citations

Adjusted Rank

Adjusted Citations

Class

Hansen MR, Moffat JC: Osteosarcoma of the skull base after radiation therapy in a patient with McCune-Albright syndrome: case report. Skull Base 13:79-83, 2003.

45

17

53

1.70

Case report

Ecke U, Luebben B, Maurer J, Boor S, Mann WJ: Comparison of different computer-aided surgery systems in skull base surgery. Skull Base 13:43-50, 2003.

45

17

53

1.70

Segal DH, Sen C, Bederson JB, Catalano P, Sacher M, Stollman AL, Lorberboym M: Predictive value of balloon test occlusion of the internal carotid artery. Skull Base Surg 5:97-107, 1995.

45

17

75

0.94

4

Ildan F, Erman T, Gös‚er A, Tuna M, Bagdatoglu H, Cetinalp E, Burgut R: Predicting the probability of meningioma recurrence in the preoperative and early postoperative period: a multivariate analysis in the midterm follow-up. Skull Base 17:157-171, 2007.

49

16

30

2.67

4

Sanosi A, Fagan PA, Biggs ND: Conservative management of acoustic neuroma. Skull Base 16:95-100, 2006.

49

16

38

2.29

4

Lee SH, Willcox TO, Buchheit WA: Current results of the surgical management of acoustic neuroma. Skull Base 12:189-195, 2002.

49

16

59

1.45

4

Simos M, Dimitrios P, Philip T: A new clinical entity mimicking meningioma diagnosed pathologically as Rosai-Dorfman disease. Skull Base Surg 8:87-92, 1998.

49

16

69

1.07

Case report

Dujovny M, Slavin KV, Hernandez G, Geremia GK, Ausman JI: Use of cerebral oximetry to monitor brain oxygenation reserves for skull base surgery. Skull Base Surg 4:117-121, 1994.

49

16

80

0.84

4

Koval J, Molcan M, Bowdler AD, Sterkers JM: Retrosigmoid transmeatal approach: an anatomic study of an approach used for preservation of hearing in acoustic neuroma surgery and vestibular neurotomy. Skull Base Surg 3:16-21, 1993.

49

16

82

0.80

Technique

Hitselberger WE, Horn KL, Hankinson H, Brackmann DE, House WF: The middle fossa transpetrous approach for petroclival meningiomas. Skull Base Surg 3:130-135, 1993.

49

16

82

0.80

Technique

Patel MR, Stadler ME, Snyderman CH, Carrau RL, Kassam AB, Germanwala AV, Gardner P, Zanation AM: How to choose? Endoscopic skull base reconstructive options and limitations. Skull Base 20:397-404, 2010.

56

15

4

5.00

4

Rosahl SK, Gharabaghi A, Hubbe U, Shahidi R, Samii M: Virtual reality augmentation in skull base surgery. Skull Base 16:59-66, 2006.

56

15

40

2.14

Review

Wanebo JE, Amin-Hanjani S, Boyd C, Peery T: Assessing success after cerebral revascularization for ischemia. Skull Base 15:215-227, 2005.

56

15

47

1.88

Review

Yilmazlar S, Arslan E, Aksoy K, Tolunay S: Sellar-parasellar brown tumor: case report and review of literature. Skull Base 14:163-168 [discussion 168], 2004.

56

15

55

1.67

Case report

Hurst RW, Howard RS, Zager E: Carotid cavernous fistula associated with persistent trigeminal artery: endovascular treatment using coil embolization. Skull Base Surg 8:225-228, 1998.

56

15

71

1.00

Case report

Lustig LR, Jackler RK: The vulnerability of the vein of labbe during combined craniotomies of the middle and posterior fossae. Skull Base Surg 8:1-9, 1998.

56

15

71

1.00

King WA, Rodts GE, Becker DP, Mc Bride DQ: Microsurgical management of giant pituitary tumors. Skull Base Surg 6:17-26, 1996.

56

15

77

0.88

4

Kanzaki J, O-Uchi T, Ogawa K, Shiobara R, Toya S: Hearing preservation by the extended and nonextended middle cranial fossa approach for acoustic neuroma. Skull Base Surg 4:76-81, 1994.

56

15

85

0.79

4

Colletti V, Bricolo A, Fiorino FG, Bruni L: Changes in directly recorded cochlear nerve compound action potentials during acoustic tumor surgery. Skull Base Surg 4:1-9, 1994.

56

15

85

0.79

4

Kirsch WM, Zhu YH, Hardesty RA, Petti G, Furnas D: Nonpenetrating clips successfully replacing sutures in base of skull surgery. Skull Base Surg 3:171-181, 1993.

56

15

87

0.75

4

Demetriades AK, Saunders N, Rose P, Fisher C, Rowe J, Tranter R, Hardwidge C: Malignant transformation of acoustic neuroma/vestibular schwannoma 10 years after gamma knife stereotactic radiosurgery. Skull Base 20:381-387, 2010.

66

14

7

4.67

Case report

El-Banhawy OA, Halaka AN, Altuwaijri MA, Ayad H, El-Sharnoby MM: Long-term outcome of endonasal endoscopic skull base reconstruction with nasal turbinate graft. Skull Base 18:297-308, 2008.

66

14

26

2.80

4

Nichols AC, Chan AW, Curry WT, Barker FG, Deschler DG, Lin DT: Esthesioneuroblastoma: the massachusetts eye and ear infirmary and massachusetts general hospital experience with craniofacial resection, proton beam radiation, and chemotherapy. Skull Base 18:327-337, 2008.

66

14

26

2.80

4

Diaz RC, Amjad EH, Sargent EW, Larouere MJ, Shaia WT: Tumors and pseudotumors of the endolymphatic sac. Skull Base 17:379-393, 2007.

66

14

36

2.33

4

Rank www.SCIENCEDIRECT.com

Review

WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.12.005

Review

EDUCATION & TRAINING

Table 3. Continued

Rank

Citations

Adjusted Rank

Adjusted Citations

Class

Bachmann-Harildstad G, Kloster R, Bajic R: Transpterygoid trans-sphenoid approach to the lateral extension of the sphenoid sinus to repair a spontaneous CSF leak. Skull Base 16:207-212, 2006.

66

14

41

2.00

Case report

Wysocki J: Cadaveric dissections based on observations of injuries to the temporal bone structures following head trauma. Skull Base 15:99-106 [discussion 106-107], 2005.

66

14

50

1.75

Technique

Jaisinghani VJ, Levine SC, Nussbaum E, Haines S, Lindgren B: Hearing preservation after acoustic neuroma surgery. Skull Base Surg 10:141-147, 2000.

66

14

68

1.08

4

Bigelow DC, Hoffer ME, Schlakman B, Hurst RW, Smith PG: Angiographic assessment of the transverse sinus and vein of labbe to avoid complications in skull base surgery. Skull Base Surg 3:217-222, 1993.

66

14

91

0.70

4

Wasserzug O, Margalit N, Weizman N, Fliss DM, Gil Z: Utility of a three-dimensional endoscopic system in skull base surgery. Skull Base 20:223-228, 2010.

74

13

10

4.33

4

Fraser JF, Mass AY, Brown S, Anand VK, Schwartz TH: Transnasal endoscopic resection of a cavernous sinus hemangioma: technical note and review of the literature. Skull Base 18:309-315, 2008.

74

13

31

2.60

Review

Baguley DM, Humphriss RL, Axon PR, Moffat DA: The clinical characteristics of tinnitus in patients with vestibular schwannoma. Skull Base 16:4958, 2006.

74

13

48

1.86

4

Sindou M, Hallacq P: Venous reconstruction in surgery of meningiomas invading the sagittal and transverse sinuses. Skull Base Surg 8:57-64, 1998.

74

13

78

0.87

4

Colletti V, Fiorino F, Mocella S, Carner M, Policante Z: “En-bloc” removal of small- to medium-sized acoustic neuromas with retrosigmoid-transmeatal approach. Skull Base Surg 7:31-38, 1997.

74

13

81

0.81

4

Jackler RK, Gladstone HB: Locating the internal auditory canal during the middle fossa approach: an alternative technique. Skull Base Surg 5:63-67, 1995.

74

13

90

0.72

Harrison LB, Pfister DG, Kraus D, Armstrong JG, Zelefsky MJ, Wiseberg J, Bosl GJ, Strong EW, Shah JP: Management of unresectable malignant tumors at the skull base using concomitant chemotherapy and radiotherapy with accelerated fractionation. Skull Base Surg 4:127-131, 1994.

74

13

92

0.68

4

Larouere MJ, Zappia JJ, Wilner HI, Graham MD, Lundy LB: Selective embolization of glomus jugulare tumors. Skull Base Surg 4:21-25, 1994.

74

13

92

0.68

4

Browne JD, Fisch U, Valavanis A: Surgical therapy of glomus vagale tumors. Skull Base Surg 3:182-192, 1993.

74

13

97

0.65

4

Pauw BK, Makek MS, Fisch U, Valavanis A: Preoperative embolization of paragangliomas (glomus tumors) of the head and neck: histopathologic and clinical features. Skull Base Surg 3:37-44, 1993.

74

13

97

0.65

4

Lobo D, Llorente JL, Suarez C: Squamous cell carcinoma of the external auditory canal. Skull Base 18:167-172, 2008.

84

12

34

2.40

4

www.WORLDNEUROSURGERY.org

Zanoletti E, Mazzoni A: Vagal paraganglioma. Skull Base 16:161-167, 2006.

84

12

52

1.71

4

Rabinov JD, Barker FG, McKenna MJ, Curtin HD: Virtual cisternoscopy: 3D MRI models of the cerebellopontine angle for lesions related to the cranial nerves. Skull Base 14:93-99 [discussion 99], 2004.

84

12

61

1.33

Roland JT Jr, Fishman AJ, Golfinos JG, Cohen N, Alexiades G, Jackman AH. Cranial nerve preservation in surgery for large acoustic neuromas. Skull base: Official Journal of North American Skull Base Society 14:85-90; discussion 90-1, 2004.

84

12

61

1.33

4

Kowalski RJ, Prayson RA, Lee JH: Skull base neurocytoma: case report and review of the literature of extraventricular neurocytomas. Skull Base 12:59-65, 2002.

84

12

67

1.09

Review

Eby JB, Cha ST, Shahinian HK: Fully endoscopic vascular decompression of the facial nerve for hemifacial spasm. Skull Base 11:189-197, 2001.

84

12

71

1.00

Review

Duong DH, O’malley S, Sekhar LN, Wright DG: Postoperative hydrocephalus in cranial base surgery. Skull Base Surg 10:197-200, 2000.

84

12

76

0.92

4

Wellman BJ, Traynelis VC, McCulloch TM, Funk GF, Menezes AH, Hoffman HT: Midline anterior craniofacial approach for malignancy: results of en bloc versus piecemeal resections. Skull Base Surg 9:41-46, 1999.

84

12

79

0.86

4

413

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Table 3. Continued

Agner C, Dujovny M, Evenhouse R, Charbel FT, Sadler L: Stereolithography for posterior fossa cranioplasty. Skull Base Surg 8:81-86, 1998.

84

12

82

0.80

Technique

Rank

Technique

Technique

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Continues

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The first rank represents the descending rank order by raw citations. The second rank (i.e., Adjusted Rank) is based on the adjusted citation index (i.e., number of citations divided by years since initial publication). The column titled Class is the class of evidence for the article based on the 2011 Oxford Centre Level of Evidence classification scheme.

Case report 16 Yang T, Rockhill J, Born DE, Sekhar LN: A case of high-grade undifferentiated sarcoma after surgical resection and stereotactic radiosurgery of a vestibular schwannoma. Skull Base 20:179-183, 2010.

Sekhar LN, Javed T: Meningiomas with vertebrobasilar artery encasement: review of 17 cases. Skull Base Surg 3:91-106, 1993.

100

11

3.67

4 100

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84

12

0.60

4

4

99

0.63

94

12 84 Chen JM, Moll C, Schotton JC, Fisch U: Inflammatory pseudotumors of the skull base. Skull Base Surg 4:93-98, 1994.

Mazzoni A, Sanna M: A posterolateral approach to the skull base: the petro-occipital transsigmoid approach. Skull Base Surg 5:157-167, 1995.

84

12

0.67

4 94 Pappas DG, Hoffman RA, Holliday RA, Hammerschlag PE, Pappas DG, Swaid SN: Evaluation and management of spontaneous temporal bone cerebrospinal fluid leaks. Skull Base Surg 5:1-7, 1995.

84

12

0.67

4 94 Shahinian H, Dornier C, Fisch U: Parapharyngeal space tumors: the infratemporal fossa approach. Skull Base Surg 5:73-81, 1995.

84

12

0.67

4

4 0.75

0.75

87

87

12

12

84

84 Tibbs RE, Bowles AP, Raila FA: Maffucci’s syndrome and intracranial chondrosarcoma. Skull Base Surg 7:49-55, 1997.

Schick B, Weber R, Kahle G, Draf W, Lackmann GM: Late manifestations of traumatic lesions of the anterior skull base. Skull Base Surg 7:77-83, 1997.

Adjusted Rank Rank

Table 3. Continued

Rank

Citations

Adjusted Citations

Class

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studies related to nonendoscopic tumor resection, biology, case series, not only describing a surgical technique; technique: studies dedicated to only description of surgical technique; vascular: studies related to vascular, biology, case series, not only describing a surgical technique; other), and level of evidence (levels 1e5 using the Oxford Centre for Evidence-Based Medicine [ OCEBM],—2011 Levels of Evidence; Appendix 1, http://www.cebm.net/index.aspx? o¼5653, and the accompanying Table of Evidence Glossary) (19). The abstract or, when necessary, the entire article was evaluated in detail to determine these characteristics and categories. RESULTS The top 100 overall most-cited works related to skull base surgery is listed in Table 2. The top 100 overall most-cited works in dedicated skull base journals is listed in Table 3.

Top 100 Overall Most-Cited Articles Related to Skull Base Surgery Demographics. Articles were published from 1965 to 2006 (Figure 1). The number of authors ranged from 1e15 with a mean, median, and mode of 5, 4, and 2, respectively. The country of the first author was most frequently the United States (n ¼ 61), followed by Canada (n ¼ 15) and Germany (n ¼ 7) (Figure 2).

Topic of Research, Study Design, and Level of Evidence. The most frequent topic was tumor/oncology (n ¼ 80), followed by articles discussing skull base vascular procedures (n ¼ 11) (Figure 3). Based on the OCEBM 2011 Levels of Evidence Classification System, 54 were classified as level 3, 34 were classified as level 4, and 12 were classified as “other.” Of the 12 “other” classified articles, there were 8 articles solely describing surgical technique, 2 articles related to surveys/grading systems, and 2 review articles.

Citation Analysis. The top 100 overall most-cited articles were referenced an average of 175  65 times (median, 157; range, 115e487). The average adjusted citation count was 8.4  4.6 (median, 7.37; range, 2.5e27.1). When comparing the adjusted ranking to the overall rank, the change in position ranged from 62 to þ87, with a mean absolute rank change of 21  17. Of the 58 articles that had 150 or more citations, 23 (40%) had an adjusted citation value of 10. Of those articles with less than 150 citations, 5 (12%) had an adjusted citation value of 10. The article with the highest combined citations overall (487, rank #1) and adjusted citation count (27.1, rank #1) was by Barker et al. (38)

Top 100 Most-Cited Articles From Dedicated Skull Base Journals Demographics. Articles were published from 1993 to 2010, with most productive single year being a tie between 1993, 1995, 2003, 2006, and 2007 (n ¼ 8) (Figure 4). The number of authors ranged from 1e9 with a mean, median, and mode of 4.5, 4, and 5, respectively. The country of the first author was most frequently the United States (n ¼ 52), followed by Italy (n ¼ 12) and Germany (n ¼ 10) (Figure 5).

Topic of Research, Study Design, and Level of Evidence. The most frequent topic was tumor/oncology (n ¼ 47), followed by articles discussing surgical technique (n ¼ 15) (Figure 6). Based on the OCEBM 2011 Levels of Evidence Classification System, 1

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Figure 3. Article counts by topic for the top overall 100 list.

Figure 1. Articles per year for the top 100 overall list.

skull base journals (4%). Most of the citations occurred in level 2 and 3 grades of evidence type studies.

DISCUSSION article was classified as level 3, 65 were classified as level 4, and 34 were classified as “other.” Of the 34 “other” classified articles, there were 9 case reports, 12 articles solely describing surgical technique, and 13 review articles.

Citation Analysis. The top 100 overall most-cited articles were referenced an average of 19  9 times (median, 16; range, 11e59). The average adjusted citation count was 2.2  1.7 (median, 1.8; range, 0.6e10.3). When comparing the adjusted ranking to the overall rank, the change in position ranged from -42 to þ84, with a mean absolute rank change of 20  15. Of the 39 articles that had 20 or more citations, 27 (69%) had an adjusted citation value of 2.0. Of those articles with less than 10 citations, 16 (26%) had an adjusted citation value of 2.0. The article with the highest combined citations overall (59, rank #1) and adjusted citation count (9.8, rank #2) was by Snyderman et al. (39) The top 100 articles were cited the most in nonskull base journals (96%) compared with

Figure 2. Article counts by country of origin for the top overall 100 list.

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The top 100 overall most-cited articles were found in 25 journals. Most of these articles were found in the Journal of Neurosurgery (n ¼ 35) and Neurosurgery (n ¼ 15). The top 100 most-cited articles in dedicated skull base periodicals were found in 3 journal titles: 1) Journal of Neurological Surgery: Part B; 2) Skull Base; and 3) Skull Base Surgery. Before 2012, the Journal of Neurological Surgery: Part B (vol. 72ecurrent) was known as Skull Base (vol. 21e71) and before 2001, Skull Base was known as Skull Base Surgery (vol. 1e21). Journal of Neurological Surgery Part B: Skull Base represents the international voice of skull base surgeons and serves as the official journal for the North American Skull Base Society, European Skull Base Society, German Skull Base Society, British Skull Base Society, Japanese Skull Base Society, and Korean Skull Base Society (25). The small amount of journals identified dedicated to skull base neurosurgery compared with the large amount of skull base

Figure 4. Articles per year for the top 100 dedicated skull base journal list.

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Figure 6. Article counts by topic for the top 100 dedicated skull base journal list.

Figure 5. Article counts by country of origin for the top 100 dedicated skull base journal list.

articles in nondedicated journals speaks to the small amount of skull base practitioners that make a large impact on the medical community. To correct for the temporal nature of citation analysis, we also present a time-adjusted citation index. This adjusted citation index was determined by dividing the raw citation count by the number of years since the article was published. An additional search was performed to determine whether any new time-adjusted article might have been missed in our overall list. No additional articles were identified in this search. The topics most recently discussed were articles related to tumor/oncology, surgical technique, and endoscopy (Figures 3 and 6). There is a bimodal distribution of the top 100 articles (Figure 4) when stratified by year of publication in the dedicated skull base journals and a unimodal distribution in nondedicated journals (Figure 1). The bimodal distribution of articles could be postulated to represent a series of seminal works that defined initial treatment paradigms followed by recent landmark studies that are slowly replacing studies now becoming obsolete. The unimodal distribution of the nondedicated journals certainly is representative of the increasing availability of journals, growth of scientific literature, and the temporal nature of citation counts—which is typical of most scientific fields. Newer articles will eventually replace the older ones in Figure 1 once sufficient time accrues, thus shifting the curve to the right but not changing its overall distribution. The articles that do not follow this pattern can be thought of as high impact articles that continue to influence the scientific community, thus achieving a higher time-adjusted citation count. The country of origin was most frequently the United States (Figures 3 and 6). There were a higher proportion of international articles in the dedicated skull base journal list. Nearly half of these articles came from international sources. Nearly all of the articles in this study were classes 3 and 4 evidence, namely retrospective case-series studies. Although there is an ubiquitous call for prospective studies in neurosurgery, these do not lend themselves easily to a highly specialized and technical field, such as skull base surgery, in which the patient volume, even at centers of excellence, is small compared with

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other neurosurgical subspecialties, such as vascular, spinal, and pediatric neurosurgery. The top 100 overall articles were referenced an average of 175  65 times, nearly a 3-fold difference from the neurosurgical classics defined in the study by Ponce and Lozano (21, 22). The top 100 articles in dedicated skull base journals were cited an average of 8.7  4.9 times, nearly a 10-fold difference from the overall list and a 20-fold difference from study by Ponce and Lozano (21, 22). The smaller field of skull base surgery lends itself to a smaller readership than, for instance, vascular neurosurgical articles, which may draw readership from a broad spectrum of individuals including neurologists to general internists. The readership of skull base surgery is much more focused and likely dominated by those directly involved in the practice of skull base surgery. Nonetheless, it is important for skull base societies to define both the landmark articles in the field and the proper way in which to use citation analysis in the future. Of the 58 articles in the overall list with a citation count of more than 150, 40% (n ¼ 23) had an adjusted citation count of 10. Of the 39 articles in the dedicated skull base journal list with a citation count of more than 20, 69% (n ¼ 27) had an adjusted citation count 2.0. The difference in ranking between the overall and timeadjusted rankings ranged from was dramatic. The overall citation count can define impact and delineate historic articles that have contributed to the skull base surgery. However, it is also important to monitor trending articles in skull base surgery. These trending articles are generating more readership—as measured by citation count—and change when normalized for time when compared with the more highly cited historic articles. The North American Skull Base Society was only recently founded in 1989, giving skull base neurosurgeons and skull base literature a much smaller time frame than that of general neurosurgery. It is our hope that studies such as this could be used by the North American Skull Base Society and other international organizations in providing skull base surgery with formalized lists of landmark and trending articles in the specialty. These lists could be published directly by skull base societies as a way to organize skull base surgical literature.

Limitations The most obvious limitation of this study is the use of citation analysis as a surrogate for impact of an article. Citation patterns have been studied in detail and generally accepted as a means to identify the ability of an article to produce readership, discussion,

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and change (18). There is a temporal limitation associated with citation analysis. Comparing raw citation counts for articles published from different time periods is problematic. We have attempted to adjust for this by the use of a time-adjusted citation index for each article.

base journal related to the subspecialty of skull base with a citation count of 150 or more and a time-adjusted citation count of 10 can be considered a high impact publication. An article in a dedicated skull base journal with an overall citation count of 20 and a time-adjusted citation count of 2.0 can be considered a high impact publication.

CONCLUSION

ACKNOWLEDGMENTS

Citation analysis has been used to organize the literature in skull base dedicated periodicals to provide lists of both trending and historic landmark articles. An original article in a nondedicated skull

The authors wish to thank Andrew J. Gienapp for technical and copy editing, preparation of the manuscript and figures for publishing, and publication assistance with this manuscript.

REFERENCES 1. Baldwin KD, Kovatch K, Namdari S, Sankar W, Flynn JM, Dormans JP: The 50 most cited articles in pediatric orthopedic surgery. J Pediatric Orthopedics Part B 21:463-468, 2012. 2. Davis RA, Cunningham PS: Creative thought in neurosurgical research: the value of citation analysis. Neurosurgery 26:345-353, 1990. 3. Dubin D, Hafner AW, Arndt KA: Citation classics in clinical dermatologic journals. Citation analysis, biomedical journals, and landmark articles, 1945-1990. Arch Dermatol 129:1121-1129, 1993. 4. Elsevier: Scopus. Available at: http://www.scopus. com. Accessed: November 20, 2013. 5. Fenton JE, Roy D, Hughes JP, Jones AS: A century of citation classics in otolaryngology-head and neck surgery journals. J Laryngol Otol 116:494-498, 2002. 6. Garfield E: ”Science Citation Index“—A new dimension in indexing. Science 144:649-654, 1964. 7. Garfield E: Citation analysis as a tool in journal evaluation. Science 178:471-479, 1972. 8. Heldwein FL, Rhoden EL, Morgentaler A: Classics of urology: a half century history of the most frequently cited articles (1955-2009). Urology 75: 1261-1268, 2010. 9. Jannetta PJ: Arterial compression of the trigeminal nerve at the pons in patients with trigeminal neuralgia. J Neurosurg 26(Suppl):159-162, 1967. 10. Jannetta PJ, Abbasy M, Maroon JC, Ramos FM, Albin MS: Etiology and definitive microsurgical treatment of hemifacial spasm. Operative techniques and results in 47 patients. J Neurosurg 47: 321-328, 1977. 11. Jinha AE: Article 50 million: an estimate of the number of scholarly articles in existence. Learned Publishing 23:258-263, 2010. 12. Jones AW: Impact of JAT publications 1981-2003: the most prolific authors and the most highly cited articles. J Analytic Toxicol 28:541-545, 2004.

15. Khan NR, Auschwitz T, McAbee JH, Boop FA, Klimo P Jr: Highly cited publications in pediatric neurosurgery: part 2. Childs Nerv Syst 29: 2215-2228, 2013. 16. Lefaivre KA, Shadgan B, O’Brien PJ: 100 most cited articles in orthopaedic surgery. Clin Orthopaed Rel Res 469:1487-1497, 2011. 17. Loonen MP, Hage JJ, Kon M: Plastic surgery classics: characteristics of 50 top-cited articles in four Plastic Surgery Journals since 1946. Plastic Reconstruc Surg 121:320e-327e, 2008. 18. Moed HF: New developments in the use of citation analysis in research evaluation. Arch Immunol Therap Exper 57:13-18, 2009. 19. OCEBM Levels of Evidence Working Group*. “The Oxford Levels of Evidence 2”. Oxford Centre for Evidence-Based Medicine. http://www.cebm.net/ index.aspx?o=5653. OCEBM Levels of Evidence Working Group = Jeremy Howick ICJLL, Paul Glasziou, Trish Greenhalgh, Carl Heneghan, Alessandro Liberati, Ivan Moschetti, Bob Phillips, Hazel Thornton, Olive Goddard and Mary Hodgkinson: OCEBM. 2013. 20. Ohba N, Nakao K, Isashiki Y, Ohba A: The 100 most frequently cited articles in ophthalmology journals. Arch Ophthalmol 125:952-960, 2007. 21. Ponce FA, Lozano AM: Highly cited works in neurosurgery. Part I: the 100 top-cited papers in neurosurgical journals. J Neurosurg 112:223-232, 2010. 22. Ponce FA, Lozano AM: Highly cited works in neurosurgery. Part II: the citation classics. J Neurosurg 112:233-246, 2010. 23. Reuters T: Web of science: Available at: http:// wokinfo.com/products_tools/multidisciplinary/ webofscience/. Accessed date: April 3, 2015. 24. Rosenberg AL, Tripathi RS, Blum J: The most influential articles in critical care medicine. J Critical Care 25:157-170, 2010.

13. Jones AW: Creme de la creme in forensic science and legal medicine. The most highly cited articles, authors and journals 1981-2003. Intern J Legal Med 119:59-65, 2005.

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27. Tripathi RS, Blum JM, Papadimos TJ, Rosenberg AL: A bibliometric search of citation classics in anesthesiology. BMC Anesthesiol 11:24, 2011. 28. Tsai YL, Lee CC, Chen SC, Yen ZS: Top-cited articles in emergency medicine. Am J Emerg Med 24:647-654, 2006. 29. Wilcox MA, Khan NR, McAbee JH, Boop FA, Klimo P Jr: Highly cited publications in pediatric neurosurgery. Childs Nerv Syst 29:2201-2213, 2013. 30. Wilkins R: Neurosurgical Classics. Park Ridge, IL: AANS; 1992. 31. Wilkins RH: Neurosurgical J Neurosurg 19:1007-1013, 1962.

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33. Wilkins RH: Neurosurgical J Neurosurg 22:294-308, 1965.

classics—Xxxi.

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Citation: World Neurosurg. (2015) 83, 4:403-418. http://dx.doi.org/10.1016/j.wneu.2014.12.005 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2015 Elsevier Inc. All rights reserved.

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APPENDIX Appendix 1. The 2011 Oxford Centre for Evidence-Based Medicine Levels of Evidence [19] Question

Level 1*

Level 2*

Level 3*

How common is the problem?

Local and current random sample surveys (or censuses)

Systematic review of surveys Local nonrandom sample that allow matching to local circumstancesy

Is this diagnostic or monitoring test accurate? (Diagnosis)

Systematic review of cross sectional studies with consistently applied reference standard and blinding

Individual cross sectional studies with consistently applied reference standard and blinding

What will happen if we do not add a therapy? (Prognosis)

Systematic review of inception cohort studies

Does this intervention help? (Treatment Benefits)

Systematic review of randomized trials or n-of-1 trials

Level 4* y

y

Level 5

Case series

n/a

Nonconsecutive studies or studies without consistently applied reference standardsy

Case-control studies or “poor or nonindependent reference standard”y

Mechanism-based reasoning

Inception cohort studies

Cohort study or control arm of randomized trial*

Case series or case-control n/a studies, or poor quality prognostic cohort studyy

Randomized trial or observational study with dramatic effect

Nonrandomized controlled cohort/follow-up studyy

Case series, case-control studies, or historically controlled studiesy

Mechanism-based reasoning

Nonrandomized controlled Case series, case-control, cohort/follow-up study or historically controlled (postmarketing surveillance) studiesy provided there are sufficient numbers to rule out a common harm. (For long-term harms the duration of follow-up must be sufficient.)y

Mechanism-based reasoning

Nonrandomized controlled cohort/follow-up studyy

Mechanism-based reasoning

Individual randomized trial or What are the COMMON Systematic review of (exceptionally) observational harms? randomized trials, study with dramatic effect (Treatment Harms) systematic review of nested case-control studies, n-of-1 trial with the patient you are raising the question about, or observational study with dramatic effect What are the RARE harms? (Treatment Harms)

Systematic review of randomized trials or n-of-1 trial

Randomized trial or (exceptionally) observational study with dramatic effect

Is this (early detection) test worthwhile? (Screening)

Systematic review of randomized trials

Randomized trial

Case series, case-control, or historically controlled studiesy

*Level may be graded down on the basis of study quality, imprecision, indirectness (study PICO does not match questions PICO), because of inconsistency between studies, or because the absolute effect size is very small; Level may be graded up if there is a large or very large effect size. yAs always, a systematic review is generally better than an individual study.

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