Introduction
The dural venous system, comprised widespread venous structures including superior sagittal (unpaired), inferior sagittal (unpaired), transverse, sigmoid, straight (unpaired), superior-inferior petrosal, tentorial, occipital (unpaired), cavernous, sphenoparietal, petrosquamous, anterior-posterior intercavernous sinuses (unpaired), torcular herophili (unpaired), basilar and falcine venous plexuses. Because of this complex texture, various variations may be seen in the dural venous system.[1]
Thrombosis and septic thrombophlebitis are the main pathological conditions of the dural venous system, which leads to severe neurological consequences and even death.[2] For the differentiation of anatomic variations and pathological conditions such as dural venous thrombosis-thrombophlebitis, anatomy and the variations of the dural venous system must be well-known to prevent misdiagnosis.[1] Advances in imaging techniques provide a better examination of main dural venous structures. Especially Computed Tomography Venography and magnetic resonance venography (MRV) are very useful for the discrimination of variations and thrombosis.[3]
In this study, we examined the frequency and associations of anatomical variations of the dural venous system in our patients by MRV.
Material and Methods
Medical records of 206 patients (41 ± 19 years old [18–78]) who underwent MRV with complaints of headache, nausea, vomiting, vertigo, seizure or neurological deficits between June 2017 and June 2019 were screened in the hospital database. Six patients were excluded from the study in whom a dural venous sinus thrombosis was detected. Among these 6 ones, thrombosis was seen in only right transverse sinus in two patients, in only superior sagittal sinus (SSS) in one patient. In two patients, left transverse + left sigmoid sinus thrombosis was detected. SSS + left transverse sinus thrombosis was observed in remained one patient. Finally, 200 patients were included in this study.
MRV examinations were performed by using a two-dimensional TOF MRV technique on GE Signa Excite 1.5 Tesla Magnetic Resonance Imaging system (Signa Excite HD; GE Medical Systems, Milwaukee, WI, USA) with a standard head coil. Time of repetition/time of echo (TR/TE) was 28/10.8, and a Flip angle of 60° was used. The field of view was 240 mm, with a matrix size of 256 × 160. Images were acquired in coronal planes with a slice thickness of 1.5 mm. Maximum pixel intensity projection images were obtained, and the images were interpreted by two radiologists. The sinuses, except occipital and falcine sinuses, were reported as normal, hypoplastic, or agenetic. Occipital and falcine sinuses were reported as absent or present.
Patients were classified into four groups as having no dural venous variation (Group C), only one variation (Group O), two variations (Group D), and three or more variations (Group T+).
The study was approved by a local ethics committee on August 06, 2019, with a number of 2019-14/142
Results
Among these 200 patients, variation was observed in 101 ones. The overall variation rate was 50.5%. The incidence of dural venous system variation was found to be as 53.85% (35/65) in males and 48.89% (66/135) in females. The variation rate was found higher in males than in females [Table 1]. These variations are believed to be occurring as a consequence of a congenital condition with no association with aging and other pathological processes as they may be seen in childhood and do not exhibit an alteration at the subsequent imaging examinations.[4]
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Table 1: Distribution of the patients to the groups according to the number of variations
Groups
In 99 patients (49.5%) (control Group 1 [C]) there was no dural venous system variation. Only one variation was detected in 33 patients (16.5%) (Group 2 [O]) [Table 2]. Two variations were observed in 52 patients (26%) (Group 3 [D]) [Table 3]. Three or more variations were seen in 16 patients (8%) (Group 4 [T+]) [Table 4].
Table 2: Distribution of the patients with one variation (Group 2) according to their variation types
Table 3: Distribution of the patients with two variations (Group 3) according to their variation types
Table 4: Distribution of the patients with three or more variations (Group 4) according to their variation types
The most common single variation was left transverse hypoplasia, which was detected in 17 patients (8.5%) [Figure 1]. Left transverse hypoplasia + left sigmoid hypoplasia was the most common dual variation that was detected in 25 patients (12.5%) [Figure 2]. The most common triple or more variations was right transverse hypoplasia + right sigmoid hypoplasia + presence of occipital sinus, which was observed in 4 patients (2%) [Figure 3].
Figure 1: Left transverse sinus hypoplasia (arrows)
Figure 2: Left transverse sinus hypoplasia (long arrows) +left sigmoid sinus hypoplasia (short arrows)
Figure 3: Right transverse sinus hypoplasia (long arrows) + right sigmoid sinus hypoplasia (short arrows) + occipital sinus (arrowheads)
There was no significant difference for the presence of complaints between the groups as the symptoms were observed with similar rates in these four groups.
Transverse sinuses
A total of 33 variations were detected in the right transverse sinus. The frequency of variation of the right transverse sinus was found to be 16.5%. Hypoplasia was observed in 30 patients while aplasia in remained three ones.
A total of 59 variations were detected in the left transverse sinus. The frequency of variation of the left transverse sinus was found to be 29.5%. Hypoplasia was observed in 56 patients, while aplasia remained three ones [Figure 4].
Figure 4: Left transverse sinus aplasia
Sigmoid sinuses
A total of 23 variations were detected in the right sigmoid sinus. The frequency of variation of the right sigmoid sinus was found to be 11.5%. Twenty-two of the variations of right sigmoid sinus were hypoplasia while one aplasia detected.
A total of 37 variations were detected in the left sigmoid sinus. The frequency of variation of the left sigmoid sinus was found to be 18.5%. Thirty-six of the variations of left sigmoid sinus were hypoplasia, while aplasia was detected in one patient.
Superior sagittal sinus
A total of two variations of the SSS were observed, while all of them were hypoplasia. No aplasia of SSS was detected. The frequency of variation of SSS was found to be 1%.
Straight sinus
A total of four variations were detected in the straight sinus. The frequency of variation of the straight sinus was found to be 2%. Three hypoplasia and one aplasia of straight sinus were observed.
Inferior sagittal sinus
A total of 11 variations were detected in the inferior sagittal sinus. The frequency of variation of the inferior sagittal sinus was found to be 5.5%. Six of the variations of inferior sagittal sinus were hypoplasia, while 5 ones were aplasia.
Occipital and falcine sinus
In 19 patients (9.5%), occipital sinus was detected. The most common variations which accompanied the presence of occipital sinus were right transverse hypoplasia + right sigmoid hypoplasia [Table 5].
Table 5: The association of presence of occipital sinus with other variations
We did not observe falcine sinus in this study.
Discussion
As the dural venous system includes various superficial and deep structures, various pathological conditions and anatomical variations can affect this system. For accurate differentiation of these physiological and pathological conditions, the variations and their association must be well known.[5] In this study, we examined the frequency and types of variations. Furthermore, we investigated the associations of these variations with each other.
We identified thirty hypoplasia and three aplasias in the right transverse sinus while the overall variation frequency of right transverse sinus was 16.5%. In 56 patients, hypoplasia and in 3 ones aplasia of the left transverse sinus was detected with a total variation frequency of 29.5%. In a study by Surendrababu et al.[6] they detected right transverse sinus hypoplasia in 13%, left transverse sinus hypoplasia in 35%, and left transverse sinus aplasia in 1% of their patients. Our results were compatible with this study regarding variation rates of right and left transverse sinuses. Goyal et al.[7] observed variation of the right transverse sinus in 6.2% of their patients (hypoplasia in 5.5% and aplasia in 0.7%). They detected hypoplasia of the left transverse sinus in 21.3% and aplasia of the left transverse sinus in 4.1% of their patients (total variation rate was 25.4%). While our left transverse sinus variation rate was similar to their results, but our right transverse sinus variation rate was markedly higher. Their bilateral transverse sinus hypoplasia rate was 1.5%. We found bilateral transverse sinus hypoplasia in our 6 patients (3%). Our bilateral transverse sinus hypoplasia rate was compatible with their study. Alper et al.[8] detected left transverse sinus hypoplasia in 39%, aplasia in 20%, right transverse sinus hypoplasia in 6%, and aplasia in 4% of their patients. When compared with their study, our left transverse sinus variation rate was lower and right transverse sinus variation rate was higher. Tantawy et al.[9] reported left transverse sinus hypoplasia in 22%, aplasia in 3.6%, right transverse sinus hypoplasia in 8%, and aplasia in 1.7% of their 363 patients. When compared with their results, our transverse sinus variation rate was higher on both sides (right and left).
We observed 23 variations in the right sigmoid sinus, while 22 of them were hypoplasia and one was aplasia. The variation rate of the right sigmoid sinus was 11.5%. There were 36 hypoplasia and one aplasia in the left sigmoid sinus with a variation rate of 18.5%. The variation rate of the left sigmoid sinus was higher than the right sigmoid sinus variation rate. In a study by Ahmed et al.[5] they detected right sigmoid sinus hypoplasia in 2.9% (n = 6) of their patients, but they did not observe right sigmoid sinus aplasia. The variation rate of left sigmoid sinus was 23.3% while they found left transverse sinus hypoplasia in 22.05% (n = 45) and aplasia in 0.98% (n = 2) of their patients. Our variation rate of the left transverse sinus was mildly lower than their results (18.5% vs. 23.3%), but we observed higher variation rates of the right sigmoid sinus (11.5% vs. 2.9%). Shirodkar et al.[10] reported right transverse sinus variations in 6% (hypoplasia in 5% and aplasia in 1%) and left transverse sinus variations in 13% (hypoplasia in 7% and aplasia in 6%) of their patients. Our results were similar to their results, but the rate of aplasia of the left transverse sinus was lower in our patients (1.5% vs. 6%).
A total of 2 variations of the SSS were observed in our study, while all of them were hypoplasia of 1/3rd of the SSS. No aplasia of SSS was detected. The rate of variation of SSS was found to be 1%. Goyal et al.[7] reported a 2.3% variation rate (0.4% (n = 6) was hypoplasia of anterior 1/3rd part) of SSS. Ahmed et al.[5] did not observe any SSS variations in their 204 patients. Our variation rate results of SSS was compatible with previous studies.
Three hypoplasia and one aplasia (2% n = 4) of straight sinus were detected in our study. Ahmed et al.[5] reported no variation of the straight sinus in their patients. Goyal et al.[7] identified 4 hypoplasia (0.2%) in their patients. We found higher variation rates of straight sinus when compared with previous studies.
Among 11 variations (5.5%) of inferior sagittal sinus variations, 6 ones were hypoplasia, and 5 ones were aplasia in our study. Ahmed et al.[5] reported a 13.95% variation rate of the inferior sigmoid sinus. Ayanzen et al.[11] detected inferior sagittal sinus in only 52% of their patients. The variation rate of the inferior sagittal sinus in our study was lower than the results of previous studies.
We detected occipital sinus in 19 patients (9.5%). Goyal et al.[7] reported occipital sinus in 1.4% of their patients. However, in literature, some studies suggested that occipital sinus was found in 4%–10%[1112] of individuals. Our occipital sinus results were similar to previous studies.
Falcine sinus is a dural venous sinus variation with an incidence of 5.3%, which may be associated with straight sinus variations.[13] We did not observe any falcine sinus in especially our patients with hypoplastic/agenetic straight sinus.
We detected dual venous sinus variations in 51 patients (25.5%). The most common dual variations were left transverse hypoplasia + left sigmoid hypoplasia (n = 25, 12.5%), right transverse hypoplasia + right sigmoid hypoplasia (n = 13, 6.5%), left transverse aplasia + left sigmoid hypoplasia (n = 2, 1%), and right transverse hypoplasia + left transverse hypoplasia (n = 2, 1%).
We observed three or more variations in 16 patients (8%). The most common three or more variations were right transverse hypoplasia + right sigmoid hypoplasia + occipital sinus (n = 4 2%), left transverse hypoplasia + left sigmoid hypoplasia + occipital sinus (n = 2 1%) and right transverse hypoplasia + left transverse hypoplasia + occipital sinus (n = 2 1%).
We observed that in the patients with multiple dural venous variations, ipsilateral transverse and sigmoid variations usually accompany each other, and also frequently an occipital sinus presents with such conditions. This is probably due to provide the drainage via the occipital sinus.
Conclusion
Multiple dural venous sinus variations may be misdiagnosed as thrombosis especially in the patients with neurological complaints as dural venous thrombosis usually involves two or more different dural sinuses. The frequency and the association of multiple variations must be well known because accurate discrimination between these variations and pathological conditions such as thrombosis is essential to prevent misdiagnosis.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Acknowledgements
We declare that there are no conflicts of interest and no funding in this study.
References
1. Joseph SC, Elias R, Tubbs RSTubbs RS, Iwanaga J, Oskouian R, Loukas M, Shoja M, Monteith S. Variations of the ıntracranial dural venous sinuses Anatomy, Imaging and Surgery of the Intracranial Dural Venous Sinuses.. 2019 St. Louis, Missouri, USA Elsevier:205–20
2. Shen X, Morón FE, Gao B. Imaging of cerebral venous complications in patients with infections Radiol Infect Dis. 2017;4:131–5
3. Kouzmitcheva E, Andrade A, Muthusami P, Shroff M, MacGregor DL, deVeber G, et al Anatomical venous variants in children with cerebral sinovenous thrombosis Stroke. 2019;50:178–80
4. Mankad K, Biswas A, Espagnet MC, Dixon L, Reddy N, Tan AP, et al Venous pathologies in paediatric neuroradiology: from foetal to adolescent life Neuroradiology. 2020;62:15–37
5. Ahmed MS, Imtiaz S, Shazlee MK, Ali M, Iqbal J, Usman R. Normal variations in cerebral venous anatomy and their potential pitfalls on 2D TOF MRV examination: Results from a private tertiary care hospital in Karachi J Pak Med Assoc. 2018;68:1009–13
6. Surendrababu NRS, Livingstone RS. Variations in the cerebral venous anatomy and pitfalls in the diagnosis of cerebral venous sinus thrombosis: Low field MR experience Indian J Med Sci. 2006;60:135–42
7. Goyal G, Singh R, Bansal N, Paliwal VK. Anatomical variations of cerebral MR venography: Is gender matter? Neurointervention. 2016;11:92–8
8. Alper F, Kantarci M, Dane S, Gumustekin K, Onbas O, Durur I. Importance of anatomical asymmetries of transverse sinuses: An MR venographic study Cerebrovasc Dis. 2004;18:236–9
9. Tantawy HF, Morsy MM, Basha MA, Nageeb RS. Different normal anatomical variations of the transverse dural sinus in magnetic resonance venography (MRV): Do age and sex matter? Eur J Anat. 2020;24:49–56
10. Shırodkar K, Reddy S, Dasappa N, Nandikoor S, Kumar GGS, Mallarajapatna G Assessment of Anatomical Variations in Cerebral Venous System Using Non Contrast Magnetic Resonance Venography 2017: European Society Of Radiology. European Congress Of Radiology: 2017. Poster no:C-2612. Available from
https://epos.myesr.org/poster/esr/ecr2017/C-2612 DOI 10.1594/ecr/2017/C-2612. [Last accessed on 2020 Oct 14].
11. Ayanzen RH, Bird CR, Keller PJ, McCully FJ, Theobald MR, Heiserman JE. Cerebral MR venography: Normal anatomy and potential diagnostic pitfalls AJNR Am J Neuroradiol. 2000;21:74–8
12. Sharma UK, Sharma K. Intracranial MR venography using low-field magnet: Normal anatomy and variations in Nepalese population J Nepal Med Assoc. 2012;52:61–5
13. Lin L, Lin JH, Guan J, Zhang XL, Chu JP, Yang ZY. Falcine sinus: Incidence and ımaging characteristics of three-dimensional contrast-enhanced thin-section magnetic resonance ımaging Korean J Radiol. 2018;19:463–9
