SBA — Single Best Answer · Review
Question 5
Anatomy → Blood vessels and nerves
Classification
Question
SSBAQuestion Header
An ultrasound-guided transversus abdominis plane block is planned for postoperative analgesia following abdominal surgery. Into which anatomical plane should the local anaesthetic be deposited?
Question Stem
A) Between external oblique and internal oblique
B) Between internal oblique and transversus abdominis
C) Between transversus abdominis and fascia transversalis
D) Between fascia transversalis and parietal peritoneum
E) Between rectus abdominis and posterior rectus sheath
B) Between internal oblique and transversus abdominis
C) Between transversus abdominis and fascia transversalis
D) Between fascia transversalis and parietal peritoneum
E) Between rectus abdominis and posterior rectus sheath
Options
A
Between external oblique and internal oblique
B
Between internal oblique and transversus abdominis
C
Between transversus abdominis and fascia transversalis
D
Between fascia transversalis and parietal peritoneum
E
Between rectus abdominis and posterior rectus sheath
Explanation
The nerves supplying the skin and muscles of the anterior abdominal wall run anteriorly in a neurovascular plane between the internal oblique and transversus abdominis muscles. These include the ventral rami of the sixth to eleventh intercostal nerves, the subcostal nerve and branches of the first lumbar nerve. A transversus abdominis plane block targets this neurovascular plane, with local anaesthetic deposited between internal oblique and transversus abdominis under ultrasound guidance. The other listed planes do not contain the neurovascular plane targeted by a TAP block.
Option Validity
A) The target neurovascular plane is deeper than the interval between external and internal oblique.
C) The nerves lie superficial to transversus abdominis rather than between that muscle and fascia transversalis.
D) The extraperitoneal plane is too deep and is not the TAP neurovascular plane.
E) The rectus sheath is not the anatomical plane targeted by a TAP block.
Further Reading
Part 1 MRCOG Revision Notes and Sample SBAs. Cambridge University Press, 2020. Section 1: Anatomy, Chapter 1. https://doi.org/10.1017/9781108644396