Enumerate the two structures passing through quadrangular space of back:
**Question:** Enumerate the two structures passing through quadrangular space of back:
A. Intervertebral Disc
B. Posterior Intercostal Artery
C. Anterior Intercostal Artery
D. Vertebral Artery
**Core Concept:**
The quadrangular space, also known as the "retrovertebral space" or "retrocrural space," is a potential space located between the posterior aspect of the first and second segments of the internal iliac artery and vein, and the first two vertebrae (T12 and L1). This space is of particular interest as it contains several vital structures that can be mistakenly punctured during procedures involving these areas, resulting in potential complications.
**Why the Correct Answer is Right:**
The quadrangular space contains two essential structures:
1. **Anterior Intercostal Artery (Option C):** This artery arises from the subclavian artery and supplies blood to the first rib and the first intercostal nerve, which innervates the first rib and first two segments of the intercostal nerves.
2. **Posterior Intercostal Artery (Option B):** Derived from the subclavian artery, it supplies blood to the ribs, intercostal nerves, and the first part of the inferior phrenic artery.
**Why Each Wrong Option is Incorrect:**
Option A, **Intervertebral Disc**, is not a structure passing through the quadrangular space but rather a structure found between the vertebrae and the intervertebral discs. Option D, **Vertebral Artery**, passes through the transverse foramen and does not directly enter the quadrangular space. The **Anterior Iliac Artery** is not mentioned as passing through this space, and the **Subclavian Artery** supplies blood to the neck and chest but not the quadrangular space.
**Core Concept:**
The quadrangular space is an important anatomical space to understand for medical students, residents, and practicing physicians due to potential complications related to puncture or injections in this area. Adequate knowledge of these structures can help prevent iatrogenic injuries and misdiagnosis during clinical procedures in the thoracic region.
**Why Each Wrong Option is Incorrect:**
1. Intervertebral disc: This option is incorrect as it is a structure found between the vertebral bodies and the intervertebral discs, not within the quadrangular space.
2. Anterior Iliac Artery: The anterior iliac artery is located within the iliacus muscle near the iliacus fossa and does not pass through the quadrangular space.
3. Subclavian Artery: The subclavian artery supplies blood to the neck and chest but not directly to the quadrangular space.
4. Posterior Iliac Artery: Like the anterior iliac artery, the posterior iliac artery is located within the iliopsoas muscle and does not pass through the quadrangular space.
**Why the Correct Answer is Right:**
The quadrangular space is