Sex differences in the splenic flexure

Abstract

INTRODUCTION

Anecdotally, surgeons claim splenic flexure mobilisation is more difficult in male patients. There have been no scientific studies to confirm or disprove this hypothesis. The implications in colorectal surgery could be profound. The aim of this study was to assess quantitatively whether there is an anatomical difference in the position of the splenic flexure between men and women using computed tomography (CT).

METHODS

Portal venous phase CT performed for preoperative assessment of colorectal malignancy was analysed using the hospital picture archiving and communication system. The splenic flexure was compared between men and women using two variables: anatomical height corresponding to the adjacent vertebral level (converted to ordinal values between 1 and 17) and distance from the midline.

RESULTS

In total, 100 CT images were analysed. Sex distribution was even. The mean ages of the male and female patients were 68.1 years and 66.7 years respectively (p=0.630). The mean vertebral level for men was 8.88, equating to the inferior half of the T11 vertebral body (range: 1–17 [superior half of T9 to inferior half of L2]), and 11.36 for women, equating to the inferior half of the T12 vertebral body (range: 4–16 [superior half of T10 to superior half of L2]). This difference was statistically significant (p=0.0001) and is equivalent to one whole vertebra. The mean distance from the midline was 160.8mm (range: 124–203mm) for men and 138.2mm (range: 107–185mm) for women (p<0.0001).

CONCLUSIONS

The splenic flexure is both higher and further from the midline in men than in women. This provides one theory as to why mobilising the splenic flexure may be more difficult in male patients.

Anecdotally, surgeons claim that mobilising the splenic flexure is more difficult in male patients. There have been no scientific studies to confirm or disprove this hypothesis. The implication in colorectal surgery can be substantial. Splenic flexure mobilisation (SFM) is associated with significant potential complications, which include haemorrhage necessitating splenectomy, longer operating time,^1,2 and decreased 30-day and 5-year survival.³ The aim of this study was to assess quantitatively whether there is an anatomical difference in the position of the splenic flexure between men and women using computed tomography (CT).

Methods

There is no universally accepted definition of what constitutes the splenic flexure. This is true for operative as well as radiological identification. Operatively, we define it as the section of the transverse colon that lies at the splenic hilum and deviates inferiorly along the lateral abdominal wall. For the purpose of this study, the radiological definition of what constituted the splenic flexure was agreed on by a consultant radiologist and the lead investigator. It was defined as the most superior and lateral aspect of the transverse colon in relation to the splenic hilum on CT.

CT was performed in the supine position with the patient in deep inspiration. All patients received a standardised volume of intravenous contrast and imaging acquired in the portal venous phase.

Portal venous CT of 100 patients (50 male, 50 female) undergoing preoperative imaging for colorectal malignancy was analysed. Patients who had undergone previous gastrointestinal surgery and those undergoing CT colonography were excluded to avoid artificially altered anatomy. All patients underwent CT in the supine position with 2mm slice thickness.

The method of anatomically siting the splenic flexure has been described in a previous paper and was found to be highly reproducible among observers.⁴ Essentially, the axial and coronal views provided on picture archiving and communication system workstations for CT interpretation are compared. The vertebral level (ie the height of the splenic flexure) is defined by the section of the vertebra to which the splenic flexure corresponds. The vertebrae were divided into three sections: superior half of body, inferior half of body and intervertebral disc (Fig 1). The distances from the midline (middle of the posterior aspect of the vertebral body) to the outermost aspect of the flexure and to the adjacent lateral abdominal wall were measured (Figs 2 and 3).

Figure 1.

The separate divisions of the vertebral level

Figure 2.

Axial computed tomography demonstrating splenic flexure (circle) and corresponding coronal image with bar correlating to splenic flexure level on axial image

Figure 3.

Axial computed tomography measuring the distance from the centre of the vertebral body to the lateral edge of the splenic flexure (A) and to the inner abdominal wall (B)

For the purposes of data analysis, the vertebral height was converted to an ordinal value ranging from 1 (superior half of the T9 vertebral body) to 17 (inferior half of the L2 vertebral body). These data were then compared using the Wilcoxon signed-rank test for paired non-parametric data in SPSS^® version 22 (IBM, New York, US). This study was exempt from Hospital Research Ethics Committee approval requirements.

Results

In total, 100 CT images were analysed. There was an even distribution between male and female patients (50:50). The mean ages of male and female subjects were 68.1 years and 66.7 years respectively (p=0.630).

The mean vertebral level for men was 8.88, equating to the inferior half of the T11 vertebral body (range: 1–17 [superior half of T9 to inferior half of L2]), and 11.36 for women, equating to the inferior half of the T12 vertebral body (range: 4–16 [superior half of T10 to superior half of L2]). This difference was statistically significant (p=0.0001) and is equivalent to one whole vertebra. The mean distance from the midline was 160.8mm (range: 124–203mm) for men and 138.2mm (range: 107–185mm) for women (p<0.0001). Conversely, the ratio of the distance of the splenic flexure from the midline relative to the distance of the lateral abdominal wall from the midline was 0.92 (range: 0.80–1.0) for men and 0.90 (range: 0.71–0.98) for women (p=0.177). The results are summarised in Table 1.

Table 1.

Summary of measurements

	Men	Women	p-value
Mean vertebral level (ordinal value for calculation)	8.88	11.36	0.0001
Mean vertebral level (anatomical)	Inferior half of T11 vertebral body	Inferior half of T12 vertebral body	0.0001
Mean distance from centre of vertebral body to lateral edge of splenic flexure (CVBL)	160.8mm	138.2mm	<0.0001
Mean distance from centre of vertebral body to inner margin of abdominal wall (CVBI)	175.1mm	153.2mm	<0.0001
Mean distance from splenic flexure to abdominal wall (CVBI – CVBL)	14.4mm	15.1mm	0.599
Ratio of CVBL to CVBI	0.92	0.90	0.177

Discussion

In our cohort of patients, the splenic flexure was on average one vertebra higher in the men than in the women. This is in keeping with our hypothesis. Our results also showed that the splenic flexure is significantly further from the midline in a man. These findings are based on CT images with a patient lying supine and may be different as patients change positions. The position in which a patient lies for CT, however, replicates the patient’s position on the operating table during abdominal surgery.

The difference in the distance of the splenic flexure from the midline is likely to result from variation between the sexes in the size of the abdominal cavity as evidenced by the absence of a significant sex difference in the ratio of the distance to the flexure relative to the distance to the lateral abdominal wall. However, from a clinical perspective, this difference is still relevant as it has technical operative implications. In contrast, the sex difference in the height of the splenic flexure represents a true anatomical variation between the sexes as it was measured relative to the vertebral bodies rather than as a specific distance. As such, this is a new anatomical finding.

Is CT a suitable technique to analyse this anatomy?

Since its introduction, CT has been reported to be a valuable method of radiological imaging of the abdomen.^5–7 It has a high degree of diagnostic accuracy regarding abdominal pathology in elective and emergency patients.⁸ Furthermore, it has been found to be accurate with regard to finely targeted interventions of the solid abdominal viscera⁹ and more recently, the colon itself.¹⁰

Is this anatomical difference important?

As mentioned above, the necessity of SFM does not only have a significant impact on a patient’s surgery (eg operative time, wound size and requirement for further intraoperative procedures such as splenectomy).^1,2 It also has a profound effect on postoperative length of stay, and short and long-term survival.³ It is therefore useful to know that there are anatomical differences between men and women that may influence the ease of performing SFM. Future research should use this information to produce a predictive score of how difficult it would be to perform SFM. This should then be validated against actual operative experience of performing SFM in scored patients.

Conclusions

The splenic flexure is both higher and further from the midline in men than in women. This provides one theory as to why mobilising the splenic flexure may be more difficult in male patients.