Understanding the Hernia Pathway Described

The question describes a hernia that extends between the layers of the abdominal wall muscles rather than passing directly through a single defect in them. This description is a classic definition used for a hernia occurring at the linea semilunaris.

Spigelian Hernia — The Correct Answer

• A Spigelian hernia occurs through the spigelian fascia, along the linea semilunaris (the lateral border of the rectus abdominis), most commonly below the level of the arcuate line.
• Its defining anatomical feature is that the hernial sac, after passing through the transversus abdominis and internal oblique aponeurosis, characteristically dissects and travels between the internal oblique and external oblique muscle layers before it may (or may not) present a palpable swelling superficially, since the external oblique aponeurosis is usually intact over it.
• This is exactly why Spigelian hernias are notoriously difficult to diagnose clinically — the defect and the visible bulge do not sit at the same point, because the sac tracks between muscle layers rather than herniating straight through them.

Why the Other Options Are Incorrect

• Richter's hernia: This refers to a hernia in which only part of the circumference of the bowel wall (not the full lumen) is trapped in the hernial defect, most often seen in femoral hernias. It describes the contents/type of incarceration, not the muscular pathway, so it does not match the description.
• Amyand's hernia: This is an inguinal hernia containing the vermiform appendix within the sac. It is defined by its contents, not by the hernia tracking between abdominal wall muscle layers.
• Littre's hernia: This is a hernia (of any type — inguinal, femoral, umbilical) containing a Meckel's diverticulum in the sac. Like the above, it is classified by content, not by an inter-muscular course.

Conclusion

Since the question is specifically about the anatomical course of the hernia — travelling between abdominal wall muscle layers instead of directly through them — the correct answer is Spigelian hernia.