The anatomy of subarachnoid space in thoracic spinal anesthesia investigated using magnetic resonance imaging among 200 Indonesian patients

Background & objective: Thoracic spinal anesthesia (TSA) is less commonly performed compared to other types of spinal anesthesia due to the risk of spinal cord injury, despite the thoracic region having a relatively wider dura-to-cord space. This study aimed to evaluate the distance between the skin, posterior dura mater, and the subarachnoid space at thoracic levels T1, T6, T9, and T12, using magnetic resonance imaging (MRI). Methodology: A total of 200 patients with medical conditions, subjected to MRI, were evaluated at Adam Malik Hospital, Medan, Indonesia. Investigations were conducted at segments T1, T6, T9 and T12 to identify the distance between skin to the posterior dura mater and subarachnoid space at thoracic levels T1, T6, T9, and T12. Results: There was no significant relationship of the patients’ age (52.03 ± 15.97 y), weight (58.44 ± 10.46 kg), and height (157.71 ± 7.03 cm) with the measurements of distance of posterior dura mater and spinal cord from the skin. The mean distance from skin to the posterior epidural was greatest at T1 (5.22 ± 1.31 cm), and the mean epidural and subarachnoid space distances were greatest at T6 level (4.21 ± 1.08 cm). Conclusion: This study identified that the subarachnoid gap is widest at the middle thoracic level, at T6 (6.41 mm) compared to the upper thoracic (T1) level (4.28 mm) and lower thoracic (T9) levels (4.63 mm), at T12 it was 4.60 mm. These anatomical variations have important implications for thoracic spinal anesthesia practice. The findings suggest that targeting the middle thoracic region for spinal injection may be associated with reduced risk of spinal cord injury, offering potential improvement in spinal anesthesia technique. Abbreviations: DTC: Dura-to-cord, IRB: Institutional Review Board, MRI: Magnetic Resonance Imaging, STROBE: Strengthening the Reporting of Observational Studies in Epidemiology, TSA: Thoracic spinal anesthesia Keywords: Anatomy; Anesthesia; Magnetic Resonance Imaging; Spinal; Subarachnoid Space Citation: Hamdi T, Daulay ER, Syarifah S, Siregar RH. The anatomy of subarachnoid space in thoracic spinal anesthesia investigated using magnetic resonance imaging among 200 Indonesian patients. Anaesth. pain intensive care 2025;29(3):514-519. DOI: 10.35975/apic.v29i3.2751 Received: October 01, 2024; Revised: February 18, 2025; Accepted: March 09, 2025