Title & Abstract

International Journal of Anatomy and Research

Exploring the Variations of the Cavernous Sinus Tributaries in the South African Population

DOI: 10.16965/ijar.2026.132

Cele, Thembelihle ¹

Lawal, Sodiq Kolawole ²

Olojede, Samuel Oluwaseun ³

Aladeyelu, Okikioluwa Stephen ⁴

Rennie, Carmen Olivia ¹⁵

¹ Discipline of Clinical Anatomy, College of Health Sciences, Nelson R. Mandela School of Medicine campus, University of KwaZulu-Natal, Durban, KwaZulu-Natal, 4000, South Africa.

² Department of Anatomy and Physiology, School of Biomedical Science and Pharmacy, University of Botswana, Private Bag 0022, Plot 4775, Notswane Road, Gaborone, Botswana.

³ Division of Human Anatomy, School of Biomedical Sciences, Faculty of Medicine and Health Sciences, Walter Sisulu University, Mthatha, 5099, South Africa.

⁴ Discipline of Clinical Anatomy, College of Health Sciences, Westville campus, University of KwaZulu-Natal, Durban, KwaZulu-Natal, 4000, South Africa.

⁵ Department of Natural and Rehabilitative Sciences, Faculty of Health Sciences, University of Fort Hare, East London, South Africa.

ABSTRACT

Background.

The cavernous sinus (CS), being the site of thrombosis, predisposes most patients to life-threatening diseases of the cavernous sinus and cerebral venous system. The procedure to treat these life-threatening diseases requires a good anatomical knowledge of CS tributaries owing to their variations in morphological and drainage patterns.

Materials and methods.

One hundred CT images of males and females were used (>13 years). In this study, the sample drawn from the Black South African population was compared to the sample drawn from the Indian and White SA population groups. The full length of each vein - the superior and inferior ophthalmic veins (SOV and IOV), the sphenoparietal sinus (SPS), and the superficial middle cerebral vein (SMCV), were observed and classified into various types according to their drainage into the cavernous sinus. These types were compared to factors such as population, age, sex and laterality.

Results.

Three morphological variations were observed for the SOV, Type S was the most prevalent in the Indian/White sample group on both sides, and more common in females. For the IOV, Type A was the most prevalent in all parameters studied. Regarding the SPS, Type A was the most prevalent, followed by Type B, and Type C was the lowest recorded. For the SMCV, Type C was the most prevalent, followed by Types A and B, with less frequencies recorded for Type D. A statistically significant association for the drainage pattern of the IOV was found on the right side for sex (p=0.03) only.

Conclusion.

The SOV showed less variations and may be an ideal vein to be used for transvenous embolisation. The use of CT images to study the pattern and variations of these veins is highly recommended before transvenous embolisation.

Keywords: Superior orbital vein; inferior orbital vein; sphenoparietal sinus; superficial middle cerebral vein; transvenous embolization

BACKGROUND

The cavernous sinus (CS) is known as a frequent site of thrombosis, which is a process of formation of blood clots in vessels in response to an infection from the face or the orbit called cellulitis [1,2]. Thrombosis of the CS can result in inflammation of the adjacent neurovascular structures, while diseases such as cavernous sinus thrombosis (CST), which are life-threatening, can result in the formation of blood clots in the CS [2]. The aetiology of these diseases could be as a result of an infection from the face, sinuses, orbital cellulitis, and pharyngitis, but they are predominantly found in patients with diabetes and thrombophilia [2]. These conditions are reported to predominantly affect women of reproductive age [2].

The CS is also a site of dural arteriovenous fistulae (dAVF), an abnormal connection between the internal or external carotid arteries, which results in the CS being fed by arteries [3]. This type of malformation is often a result of traumatic brain injury, embryological defects, surgery, and/or genetic conditions [3]. This condition is normally found unilaterally; however, the majority of females were found to possess bilaterality (90%, p=0.043) of this condition, although it is also found unilaterally in males (10%) [3].

Among the life-threatening disorders affecting the CS is cerebral venous sinus thrombosis (CVST), a type of stroke normally found in women in their reproductive ages [4]. Although the exact aetiology of the disease is not known, it is found to affect women on oral contraceptives, during pregnancy, and in the peripartum period [5,6]. Previous literature has documented the use of contraceptives in relation to CVST, and a significant association was obtained which confirmed that females are the most vulnerable to this disease [4]. A systematic review study on CVST in sub-Saharan Africa found a very high prevalence of women with CVST (58.6%) [6].

Surgical interventions to these cerebral venous sinus diseases in the skull base have resulted in very high mortality and morbidity rates (10%) in sub-Saharan Africa [5,6]. This is owing to intracranial bleeding caused by the rupture of veins during surgical procedures [5-7]. Endovascular embolisation has been the treatment of choice for this condition because it is safer and possesses low complication rates [3]. Access to the CS when performing endovascular embolisation is through the inferior petrosal sinus (IPS), but if it is occluded, the point of access will be through the facial and ophthalmic veins [3]. Although endovascular embolisation is declared safe, veins used in accessing the CS have numerous variations in morphology and drainage patterns, making the procedure difficult [8].

The CS receives communication from numerous para-cavernous sinus structures such as the superior and inferior ophthalmic veins [1,9,10]. The superior ophthalmic vein (SOV) runs between the optic nerve and superior rectus muscle and exits the orbit via the superior orbital fissure to drain into the CS [11,12]. The inferior ophthalmic vein (IOV), located in the midorbit slightly superior to the inferior rectus muscle, drains either into the SOV or directly into the CS [11]. The sphenoparietal sinus (SPS) receives blood from the superficial middle cerebral vein (SMCV) before emptying into the CS [9,13]. The current study, using CT images, aimed to report on the variable patterns of CS tributaries in the South African population with comparison to sex, age, and laterality.

MATERIALS AND METHODS

Sample Size and Population

This was a retrospective analysis of 100 CT scans of adult individuals (56 males, 44 females; 200 sides total) obtained from Inkosi Albert Luthuli Central Hospital (IALCH) in Durban, KwaZulu-Natal, South Africa. The CT images were of 13 years of age and above, classified into age categories: <=29, 30-39, 40-49, 50-59, 60-69, 70-79, and >=80 years. Due to data distribution, the Indian and White sample groups were merged into one sample (29; 29%) and compared to the Black sample (71; 71%).

Materials, Scanning Protocol, and Criteria

A total of 100 CT images from CT venograms and CT angiograms (with venous phase) were viewed and analyzed using syngo.plaza viewer software (version VB10) in axial and sagittal planes. Scanners used included Multi-Detector row CT (MDCT) Scanners (Lightspeed CT, GE Healthcare and SOMATOM Definition Flash CT, Siemens Healthineers) with 1mm and 2mm slice configurations. Inclusion criteria comprised scans of patients >13 years depicting both cerebral hemispheres with slice thickness 1-2 mm. Exclusion criteria comprised scans with observable venous vascular pathologies (AVMs, dAVF, brain tumours, veno-occlusive diseases). Ethical clearance was obtained from the Biomedical Research Ethics Committee (BREC) at UKZN (BREC/00005683/2023).

Study Procedure and Tributary Classification

Four CS tributaries were evaluated: 1) Superior Ophthalmic Vein (SOV): classified as Type S (straight from anterior to posterior), Type T-A (tortuous anteriorly/distally), or Type T-P (tortuous posteriorly/proximally); 2) Inferior Ophthalmic Vein (IOV): Type A (drains into SOV before CS) or Type B (drains directly into CS); 3) Sphenoparietal Sinus (SPS): Type A (drained into CS only), Type B (drained into CS and pterygoid plexus via SEVs), or Type C (hypoplastic/poorly formed); 4) Superficial Middle Cerebral Vein (SMCV): Type A (drained into SPS before CS), Type B (drained laterally into CS), Type C (connected to SEVs and pterygoid plexus), or Type D (drained into superior petrosal/transverse sinus posteriorly).

Statistical Analysis

Stata version 17 (StataCorp, College Station, Texas, USA) statistical software was used for analysis with significance level set at p < 0.05. Descriptive statistics, Chi-square tests, Mann-Whitney, and Kruskal-Wallis non-parametric tests were performed.

RESULTS

1. Superior Ophthalmic Vein (SOV)

Three morphological patterns of the SOV were observed: Type S, Type T-A, and Type T-P (Figure 1). Bilaterally identical configurations occurred in 50% of the population: 38% Type S, 7% Type T-A, and 5% Type T-P (Table 1). Type S was the most prevalent across both Black SA (50.7% left, 59.2% right) and Indian/White SA (62.1% left, 65.5% right), as well as across sexes (females: 61.4% left, 65.9% right; males: 48.2% left, 57.1% right) (Table 2).

Table 1

Showing CTs with the same configuration of the superior ophthalmic vein on the left and right sides (%).

Left \ Right | S | T-A | T-P | Total
S | 38 | 6 | 10 | 54
T-A | 14 | 7 | 10 | 31
T-P | 9 | 1 | 5 | 15
Total | 61 | 14 | 25 | 100

Table 2

The morphology of the SOV compared to population, sex, age, and laterality.

Parameter | Left S N (%) | Left T-A N (%) | Left T-P N (%) | Left p-value | Right S N (%) | Right T-A N (%) | Right T-P N (%) | Right p-value
Population: Indian/White SA | 18 (62.1%) | 6 (20.7%) | 5 (17.2%) | 0.36 | 19 (65.5%) | 3 (10.3%) | 7 (24.1%) | 0.76
Population: Black SA | 36 (50.7%) | 25 (35.2%) | 10 (14.1%) | - | 42 (59.2%) | 11 (15.5%) | 18 (25.4%) | -
Sex: Female | 27 (61.4%) | 9 (20.5%) | 8 (18.2%) | 0.13 | 29 (65.9%) | 5 (11.4%) | 10 (22.7%) | 0.65
Sex: Male | 27 (48.2%) | 22 (39.3%) | 7 (12.5%) | - | 32 (57.1%) | 9 (16.1%) | 15 (26.8%) | -
Age: <=29 | 13 (56.5%) | 7 (30.4%) | 3 (13.0%) | 0.24 | 12 (52.2%) | 5 (21.7%) | 6 (26.1%) | 0.95
Age: 30-39 | 17 (56.7%) | 8 (26.7%) | 5 (16.7%) | - | 18 (60.0%) | 5 (16.7%) | 7 (23.3%) | -
Age: 40-49 | 8 (40.0%) | 11 (55.0%) | 1 (5.0%) | - | 12 (60.0%) | 2 (10.0%) | 6 (30.0%) | -
Age: 50-59 | 10 (76.9%) | 1 (7.7%) | 2 (15.4%) | - | 8 (61.5%) | 2 (15.4%) | 3 (23.1%) | -
Age: 60-69 | 3 (33.3%) | 3 (33.3%) | 3 (33.3%) | - | 6 (66.7%) | 0 (0.0%) | 3 (33.3%) | -
Age: 70-79 | 2 (50.0%) | 1 (25.0%) | 1 (25.0%) | - | 4 (100.0%) | 0 (0.0%) | 0 (0.0%) | -
Age: >=80 | 1 (100.0%) | 0 (0.0%) | 0 (0.0%) | - | 1 (100.0%) | 0 (0.0%) | 0 (0.0%) | -

Figure 1: Superior Ophthalmic Vein morphological variations

2. Inferior Ophthalmic Vein (IOV)

Two drainage patterns of the IOV were observed: Type A (draining into SOV) and Type B (draining directly into CS) (Figure 2). Forty-two percent of patients had Type A bilaterally, while 24% had Type B bilaterally (Table 3). Type A predominated on both left (58.0%) and right (60.0%) sides. A statistically significant association was observed on the right side for sex (p = 0.03), where males had higher Type A (69.6%) and females had higher Type B (52.3%) (Table 4).

Table 3

Showing patients with the same pattern of the inferior ophthalmic vein on the left and right sides (%).

Left \ Right | A | B | Total
A | 42 | 16 | 58
B | 18 | 24 | 42
Total | 60 | 40 | 100

Table 4

The drainage pattern of the IOV compared to population, sex, age, and laterality.

Parameter | Left A N (%) | Left B N (%) | Left p-value | Right A N (%) | Right B N (%) | Right p-value
Population: Indian/White SA | 17 (58.6%) | 12 (41.4%) | 0.94 | 20 (69.0%) | 9 (31.0%) | 0.24
Population: Black SA | 41 (57.7%) | 30 (42.3%) | - | 40 (56.3%) | 31 (43.7%) | -
Sex: Female | 26 (59.1%) | 18 (40.9%) | 0.84 | 21 (47.7%) | 23 (52.3%) | 0.03*
Sex: Male | 32 (57.1%) | 24 (42.9%) | - | 39 (69.6%) | 17 (30.4%) | -
Age: <=29 | 16 (69.6%) | 7 (30.4%) | 0.14 | 19 (82.6%) | 4 (17.4%) | 0.07
Age: 30-39 | 17 (56.7%) | 13 (43.3%) | - | 19 (63.3%) | 11 (36.7%) | -
Age: 40-49 | 10 (50.0%) | 10 (50.0%) | - | 9 (45.0%) | 11 (55.0%) | -
Age: 50-59 | 6 (46.2%) | 7 (53.8%) | - | 7 (53.8%) | 6 (46.2%) | -
Age: 60-69 | 8 (88.9%) | 1 (11.1%) | - | 3 (33.3%) | 6 (66.7%) | -
Age: 70-79 | 1 (25.0%) | 3 (75.0%) | - | 2 (50.0%) | 2 (50.0%) | -
Age: >=80 | 0 (0.0%) | 1 (100.0%) | - | 1 (100.0%) | 0 (0.0%) | -

Figure 2: Inferior Ophthalmic Vein drainage patterns

3. Sphenoparietal Sinus (SPS)

Three drainage patterns of the SPS were observed: Type A (drained into CS only), Type B (drained into CS and pterygoid plexus), and Type C (hypoplastic) (Figure 3). Fifty-four percent of patients had bilaterally identical configurations (37% Type A, 15% Type B, 2% Type C) (Table 5). Type A predominated on both left (62.0%) and right (55.0%) sides, followed by Type B (29.0% left, 39.0% right), while Type C was least common (9.0% left, 6.0% right) (Table 6). Indian/White individuals exhibited no Type C cases bilaterally.

Table 5

CTs with the same configuration of the sphenoparietal sinus on the left and right sides (%).

Left \ Right | A | B | C | Total
A | 37 | 22 | 3 | 62
B | 13 | 15 | 1 | 29
C | 5 | 2 | 2 | 9
Total | 55 | 39 | 6 | 100

Table 6

The drainage pattern of the sphenoparietal sinus compared to population, sex, age, and laterality.

Parameter | Left A N (%) | Left B N (%) | Left C N (%) | Left p-value | Right A N (%) | Right B N (%) | Right C N (%) | Right p-value
Population: Indian/White | 21 (72.4%) | 8 (27.6%) | 0 (0.0%) | 0.11 | 16 (55.2%) | 13 (44.8%) | 0 (0.0%) | 0.25
Population: Black | 41 (57.7%) | 21 (29.6%) | 9 (12.7%) | - | 39 (54.9%) | 26 (36.6%) | 6 (8.5%) | -
Sex: Female | 27 (61.4%) | 12 (27.3%) | 5 (11.4%) | 0.75 | 23 (52.3%) | 18 (40.9%) | 3 (6.8%) | 0.88
Sex: Male | 35 (62.5%) | 17 (30.4%) | 4 (7.1%) | - | 32 (57.1%) | 21 (37.5%) | 3 (5.4%) | -
Age: <=29 | 17 (73.9%) | 5 (21.7%) | 1 (4.3%) | 0.64 | 14 (60.9%) | 7 (30.4%) | 2 (8.7%) | 0.98
Age: 30-39 | 19 (63.3%) | 9 (30.0%) | 2 (6.7%) | - | 16 (53.3%) | 13 (43.3%) | 1 (3.3%) | -
Age: 40-49 | 8 (40.0%) | 10 (50.0%) | 2 (10.0%) | - | 11 (55.0%) | 7 (35.0%) | 2 (10.0%) | -
Age: 50-59 | 7 (53.8%) | 4 (30.8%) | 2 (15.4%) | - | 7 (53.8%) | 5 (38.5%) | 1 (7.7%) | -
Age: 60-69 | 6 (66.7%) | 1 (11.1%) | 2 (22.2%) | - | 5 (55.6%) | 4 (44.4%) | 0 (0.0%) | -
Age: 70-79 | 1 (25.0%) | 3 (75.0%) | 0 (0.0%) | - | 2 (50.0%) | 2 (50.0%) | 0 (0.0%) | -
Age: >=80 | 0 (0.0%) | 1 (100.0%) | 0 (0.0%) | - | 0 (0.0%) | 1 (100.0%) | 0 (0.0%) | -

Figure 3: Sphenoparietal Sinus drainage patterns

4. Superficial Middle Cerebral Vein (SMCV)

Four drainage patterns of the SMCV were observed: Type A (drained into SPS), Type B (drained laterally into CS), Type C (connected to SEVs and pterygoid plexus), and Type D (drained into superior petrosal/transverse sinus) (Figure 4). Thirty-six percent of patients exhibited bilaterally identical patterns (7% Type A, 3% Type B, 20% Type C, 6% Type D) (Table 7). Type C was the most prevalent overall on both left (47.0%) and right (38.0%) sides, followed by Type A and Type B (each 19.0% left, 23.0% right), while Type D was least frequent (15.0% left, 16.0% right) (Table 8).

Table 7

Showing CT with the same pattern of the superficial middle cerebral vein (%).

Left \ Right | A | B | C | D | Total
A | 7 | 2 | 6 | 4 | 19
B | 5 | 3 | 8 | 3 | 19
C | 9 | 15 | 20 | 3 | 47
D | 2 | 3 | 4 | 6 | 15
Total | 23 | 23 | 38 | 16 | 100

Table 8

The drainage pattern of the superficial middle cerebral vein compared to population, sex, age, and laterality.

Parameter | Left A N (%) | Left B N (%) | Left C N (%) | Left D N (%) | Left p-value | Right A N (%) | Right B N (%) | Right C N (%) | Right D N (%) | Right p-value
Population: Indian/White | 3 (10.3%) | 7 (24.1%) | 14 (48.3%) | 5 (17.2%) | 0.51 | 10 (34.5%) | 6 (20.7%) | 11 (37.9%) | 2 (6.9%) | 0.21
Population: Black | 16 (22.5%) | 12 (16.9%) | 33 (46.5%) | 10 (14.1%) | - | 13 (18.3%) | 17 (23.9%) | 27 (38.0%) | 14 (19.7%) | -
Sex: Female | 8 (18.2%) | 8 (18.2%) | 23 (52.3%) | 5 (11.4%) | 0.75 | 11 (25.0%) | 14 (31.8%) | 14 (31.8%) | 5 (11.4%) | 0.2
Sex: Male | 11 (19.6%) | 11 (19.6%) | 24 (42.9%) | 10 (17.9%) | - | 12 (21.4%) | 9 (16.1%) | 24 (42.9%) | 11 (19.6%) | -
Age: <=29 | 4 (17.4%) | 8 (34.8%) | 5 (21.7%) | 6 (26.1%) | 0.18 | 8 (34.8%) | 4 (17.4%) | 8 (34.8%) | 3 (13.0%) | 0.06
Age: 30-39 | 5 (16.7%) | 14 (46.7%) | 5 (16.7%) | 6 (20.0%) | - | 4 (13.3%) | 6 (20.0%) | 11 (36.7%) | 9 (30.0%) | -
Age: 40-49 | 9 (45.0%) | 7 (35.0%) | 3 (15.0%) | 1 (5.0%) | - | 4 (20.0%) | 6 (30.0%) | 9 (45.0%) | 1 (5.0%) | -
Age: 50-59 | 0 (0.0%) | 2 (15.4%) | 10 (76.9%) | 1 (7.7%) | - | 0 (0.0%) | 5 (38.5%) | 6 (46.2%) | 2 (15.4%) | -
Age: 60-69 | 1 (11.1%) | 2 (22.2%) | 5 (55.6%) | 1 (11.1%) | - | 5 (55.6%) | 0 (0.0%) | 3 (33.3%) | 1 (11.1%) | -
Age: 70-79 | 0 (0.0%) | 3 (75.0%) | 1 (25.0%) | 0 (0.0%) | - | 2 (50.0%) | 2 (50.0%) | 0 (0.0%) | 0 (0.0%) | -
Age: >=80 | 0 (0.0%) | 1 (100.0%) | 0 (0.0%) | 0 (0.0%) | - | 0 (0.0%) | 0 (0.0%) | 1 (100.0%) | 0 (0.0%) | -

Figure 4: Superficial Middle Cerebral Vein drainage patterns

DISCUSSION

Diseases of the dural venous sinuses, such as the CST and CVST, are life-threatening disorders that result in the formation of blood clots in the CS [3,4,19]. These diseases have been linked to high morbidity and mortality rates [5]. Additionally, the CS is also a site of dAVF that are said to be treated with endovascular embolisation [20]. This is the safest and most effective method for managing CS diseases that require surgical intervention [20]. The transvenous type of embolisation uses the IPS to access the CS [21]. However, if the IPS is obstructed, the SOV may be used as an alternative [21,22].

Knowledge of the drainage patterns of the tributaries draining into the CS is essential in the transvenous embolisation of diseases affecting the CS. The SOV may be used for transvenous access to the CS, as it presented with less variations in terms of morphology. However, if not assessed properly, it may result into serious clinical complications. Therefore, adequate CT analysis must be done before attempting to access the CS using the SOV. The IOV may be used depending on an individual's venous anatomy. If it has a high incidence of Type A, it could cause embolisation of the SOV and neighbouring structure if it is used to access the CS. To prevent cortical venous reflux into the CS during transvenous embolisation, it is important for clinicians to be aware of the drainage patterns of the SMCV as well as its connection with SPS.

Variations of the CS tributaries were noted across different population groups, sex, as well as age. Therefore, the use of CT images in the assessment of cerebral venous anatomy and diagnosis of venous sinus diseases is essential in clinical settings before deciding on the appropriate treatment method. Although there was a slight difference with regards to sex across all the veins studied, it was statistically significant: IOV (p = 0.03). These variations must be considered in the diagnosis and treatment of venous sinus diseases. One CT in the >= 80 years age group was found to have variations on the left and right sides. However, this CT presented with same pattern for the SOV (S Type) and SPS (Type B) on the left and right sides. However, for the IOV and the SMCV, the same CT presented with different patterns on the left and right sides: IOV (left - Type B: right - Type A) and SMCV (left - Type B: right - Type C). This shows that different veins may be used to access the CS for the same patient, as there may present with variations of the same vein on both sides.

a) The superior ophthalmic vein

Several studies have observed the tortuosity of the SOV, which sometimes becomes an obstruction in the access of the CS using the transvenous approach [12,14,22-24]. The study by Kurata et al. [22] observed the tortuosity of the SOV in three of the ten patients who were examined. The tortuosity of the SOV was observed distally on the left side in those three patients [22]. This is in line with the current study, as the left side had a high incidence of SOV with Type T-A (tortuous anteriorly) compared to the right side in sex, population, and age. Both sides can have different morphological patterns of the SOV; therefore, assessment of the SOV is crucial before performing transvenous embolization.

In a study by Wolfe et al. [23], out of the ten patients that were studied, one CT presented with tortuosity of the SOV on the left side, which resulted in the rupture of the vein during the direct surgical SOV approach as well as the retrograde transvenous embolization procedure. Despite this incident, they still recommend the use of the SOV as an alternative in accessing the CS by direct surgical cannulation if the IPS, superior petrosal sinus, and the intercavernous sinus are obstructed [23]. This agrees with the present study as the tortuosity of the SOV both anteriorly and posteriorly was less compared to the straight pattern of the SOV. This implies that the SOV can be used for transvenous embolisation in the SA population as this will limit the amount of venous rupture and intracranial bleeding during surgery.

Additionally, the study by Tsutsumi et al. [12] observed the whole course of the SOV, and its proximal part was found to be variable. Out of 46 patients examined, five (11%) patients had a tortuous proximal segment on the right side, and three (6.5%) patients presented with a tortuous proximal segment on the left side. This also agrees with the present study, as variations between the left and right sides were evident. This suggests that each CT may present with different patterns of the SOV on the left and right sides.

b) The inferior ophthalmic vein

Venous sinuses are often assumed to facilitate the spread of infection from extracranial to intracranial by the SOV and IOV to the CS, which in turn leads to life-threatening septic cavernous thrombosis [26-28]. The IOV is said to converge with the SOV before draining into the CS [11,26,29]. Zhang and Stringer [26] observed a similar drainage pattern of the IOV in their study; however, the prevalence of these findings was not reported. Cheung and McNab [11] also observed a similar pattern in three out of ten orbital dissections.

This is in agreement with the current study as the prevalence of Type A was high when compared to Type B in both population groups and both sexes, with a statistical significance of p = 0.03 found on the right for sex. It is worth noting that Cheung and McNab (2003) observed the IOV draining directly into the CS, bypassing the SOV in two orbital dissections. Similar to the current study, low incidents of Type B were obtained for population, sex, and age. This implies that most individuals in SA are likely to present with Type A, and this can result in complications like embolisation of unintended areas as well as damage to surrounding structures like rupture of the SOV.

c) The sphenoparietal sinus

The SPS has been identified as a venous channel found under the lesser wing of the sphenoid bone, and it receives drainage from the SMCV [30; 31]. The relationship between the SPS and the SMCV in terms of their drainage has been studied previously [9,13,30]. However, these studies were more concerned about the drainage of the SMCV and less on the SPS.

Tanoue et al. [9] observed three different patterns of the SPS which were also observed in the current study. Out of the 37 patients that were assessed, Type A (72%) was the most prevalent, followed by Type C (14%), and Type B (4%) was the least prevalent in the Japanese study [9]. The current study agrees with the Tanoue et al., [9] as Type A was the most prevalent in all the parameters (population, sex, and age) studied on both the left and right sides. However, Type A was followed by Type B, and fewer incidences were recorded in the present study for Type C. It is important to note that the Indian/White sample group did not present with Type C on both the left and right sides. This assumes that it is possible to access the CS using the SPS in the Indian/White sample group, as the course of the SPS was observed in most patients coursing from the pterion along the lesser wing of the sphenoid to its termination in the CS (Type A).

d) The superficial middle cerebral vein

The SMCV is one of the venous channels essential in the transvenous embolisation of the cavernous sinus dural arteriovenous fistula (CSDAF) [31]. It has been observed in previous studies, and it was said to drain either to the SPS before draining into the CS or just directly to the CS (9; 13; 31]. However, some authors have noted several drainage patterns of the SMCV to the CS. A study of 24 patients observed four drainage patterns where the SMCV drained into the anterolateral aspect of the CS in 35.4% of the patients; drained into the foramen ovale in 10.4% of the patients; 16.7% of the population had their SMCV draining into the lateral aspect of the CS and in 35.4% of the population they could not identify the SMCV [31]. Suzuki and Matsumoto [13] and Ikushima et al. [33] observed seven drainage patterns of the SMCV, which were classified according to their termination points as SPS, CS, Superior petrosal sinus, basal type, squamosal type, as well as the underdeveloped type.

The studies by Suzuki and Matsumoto [13] and Ikushima et al. [33] observed a high prevalence of the SPS type in their studies - 58% and 54% respectively. Tanoue et al. [9] observed four drainage patterns of the SMCV as observed by the present study and were classified into Type A - SPS, Type B - CS, Type C - SEV, and Type D - Superior petrosal sinus. Type A was the most prevalent in their study with Type D being the least recorded [9]. Contrary to the present study, Type C was the most prevalent, but Type D was the least recorded similar to previous studies, with notable differences on the left and right sides.

There were similar findings for Types A and B for females and males on the left side (18.2% and 19.6%, respectively). Similarly, in previous studies, patients with the same or mixed types on the left and right sides were observed as indicated in Table 7 [9]. This implies that the pattern of the SMCV may be challenging to use for transvenous access to the CS as it is small and variable. It can pose a high risk to surrounding structures like the middle meningeal artery, but it can be used as a potential access point for malformations and CSDAF. However, this will depend on individual patients' anatomy as the SMCV may not drain directly to the CS but drain to the pterygoid plexus through the SEVs and to the superior petrosal sinus/transverse sinus.

CONCLUSION

In this South African study population, the IOV, SPS, and SMCV exhibited significant anatomical variability, posing risks of clinical complications during transvenous embolisation. Conversely, the SOV demonstrated greater morphological consistency (Type S predominance) and represents a more viable alternative access route. Pre-procedural CT imaging is highly recommended to map individual venous variations and mitigate risks.

Abbreviations & Declarations

ABBREVIATIONS

CS: Cavernous Sinus

CSDAF: Cavernous Sinus Dural Arteriovenous Fistula

CST: Cavernous Sinus Thrombosis

CT: Computed Tomography

CVST: Cerebral Venous Sinus Thrombosis

dAVF: Dural Arteriovenous Fistulae

FB: Frontal Bone

FO: Foramen Ovale

FS: Frontal Sinus

IALCH: Inkosi Albert Luthuli Central Hospital

IOV: Inferior Ophthalmic Vein

IPS: Inferior Petrosal Sinus

LP: Lamina Papyracea

MDCT: Multi-Detector Computed Tomography

MRA: Magnetic Resonance Angiography

SA: South Africa

SEV: Sphenoid Emissary Vein

SMCV: Superficial Middle Cerebral Vein

SOF: Superior Orbital Foramen / Fissure

SOV: Superior Ophthalmic Vein

SPS: Sphenoparietal Sinus

ACKNOWLEDGMENTS

The authors would like to acknowledge all the supervisors who contributed to the success of this project, the Department of Clinical Anatomy, the Department of Health, and the Inkosi Albert Luthuli Central Hospital. The author would like to appreciate the National Research Foundation for funding the study.

DECLARATIONS

Ethical Approval: Ethical clearance was obtained from the Biomedical Research Ethics Committee (BREC) at the University of KwaZulu-Natal (BREC/00005683/2023).

Conflicts of Interest: None.

Author Contributions: TC and COR designed the experiments; TC performed experiments and collected data; TC, COR, OSA, SKL, and SOO discussed results and strategy; COR supervised, directed, and managed the study; COR, OSA, SKL, and SOO assisted in structuring and writing of the manuscript; TC, COR, OSA, SOO, and SKL approved the final version.

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