The Mesorchium: Anatomical Definition and Clinical Significance
The mesorchium is a peritoneal fold that suspends the testis within the tunica vaginalis, serving as a mesentery-like structure that contains blood vessels and nerves supplying the testis.
Anatomical Structure and Development
The mesorchium represents a critical anatomical structure in testicular development and positioning:
- It forms as part of the genital peritoneal folds during embryonic development
- Develops from the plica mesonephrica (the first visible fold of urogenital organs) 1
- Can be divided into proximal and distal portions:
- Proximal mesorchium: originates from the plica mesonephrica
- Distal mesorchium: evolves from the plica suspensoria gonadalis 1
Anatomical Relationship to Surrounding Structures
The mesorchium has important anatomical relationships:
- Attaches the testis to the posterior wall of the tunica vaginalis
- Contains the testicular blood vessels and nerves that supply the testis
- Forms part of the suspensory apparatus of the testis
- Represents the testicular equivalent of the mesovarium in females 1
Age-Related Changes
The relationship between the testis and tunica vaginalis changes significantly with age:
- In fetuses and children: The testis is clearly intraperitoneal with a well-defined mesorchium 2, 3
- After age 50: Secondary adhesions form between the tunica vaginalis and testis, progressively obliterating the mesorchium 2
- In advanced age: The tunica vaginalis shrinks and adheres to the testis, making it appear to be behind rather than within the tunica vaginalis 2
Clinical Significance
The mesorchium has several important clinical implications:
1. Testicular Torsion
The anatomical configuration of the mesorchium directly impacts the risk of testicular torsion:
- Long mesorchium: Associated with increased mobility of the testis and higher risk of torsion 4
- In a study of 50 testes with torsion, 8 (16%) had a long mesorchium, with 4 of these presenting with torsion 4
- Bell clapper deformity (abnormal attachment of the tunica vaginalis) is frequently associated with intravaginal torsion and was found in 80% of testes in patients with torsion 4
2. Pathological Considerations
- The mesorchium appears to be a major mesothelial target site for certain carcinogenic processes 5
- In animal studies, the mesorchium showed the highest incidence of mesothelioma formation compared to other mesothelial surfaces 5
3. Surgical Relevance
Understanding the mesorchium is crucial during:
- Orchidopexy procedures
- Testicular torsion repair
- Varicocele surgery
- Hydrocele repair
Anatomical Variations
The relationship between the testis and epididymis can vary, which affects the mesorchium configuration:
- Type I (76% of cases): Epididymis united to the testis by its head and tail
- Type II (12%): Epididymis totally united to the testis
- Type III (12%): Disjunction of epididymal tail 4
These variations can influence the mobility of the testis and its susceptibility to torsion.
Common Misconceptions
A significant discrepancy exists between anatomical texts and clinical observations:
- Adult anatomy texts often describe the testis as "behind" the tunica vaginalis
- In pediatric surgery, the testis clearly appears to be inside the tunica vaginalis 2, 3
- This difference is explained by the age-related changes in the mesorchium, with progressive adhesions forming in adulthood 2
Understanding these age-related changes is essential for proper surgical approach and interpretation of anatomical findings in different age groups.