What is the most common anomaly of splenic (spleen) embryology?

Accessory Spleen: The Most Common Anomaly of Splenic Embryology

The most common anomaly of splenic embryology is an accessory spleen (option B). Accessory spleens are congenital foci of splenic tissue that develop separately from the main spleen due to failure of the splenic anlage to fuse during embryological development.

Epidemiology and Characteristics

• Accessory spleens occur in approximately 10-30% of the general population, making them the most common splenic embryological anomaly 1
• During routine splenectomy procedures, accessory spleens are observed in approximately 15% of patients 2
• They are most commonly located at or near the splenic hilum (most frequent site), but can also be found in other locations including the pancreatic tail, greater omentum, splenic ligaments, and even rarely in the parietal peritoneum 3, 4
• The size of accessory spleens typically ranges from 1-3.5 cm in length and 0.5-2.5 cm in width 1

Clinical Significance

• Most accessory spleens are asymptomatic and discovered incidentally during imaging studies, surgery, or autopsy 3
• In patients undergoing splenectomy for hematological disorders (such as idiopathic thrombocytopenic purpura), undetected accessory spleens can be responsible for disease recurrence 2, 1
• Approximately 12% of patients who fail splenectomy or relapse after splenectomy are found to have an accessory spleen by radionuclide imaging 2
• Accessory spleens may mimic tumors in various locations, particularly in the pancreatic tail, adrenal gland, stomach or intestine, potentially leading to unnecessary diagnostic procedures 3, 5

Diagnostic Considerations

• Contrast-enhanced CT, MRI, and ultrasound can identify accessory spleens, but may sometimes be confused with other lesions 5
• Nuclear medicine examinations using technetium-99m-labeled red blood cells or sulfur colloid can confirm the presence of splenic tissue and differentiate accessory spleens from other pathologies 5
• Histologically, accessory spleens contain the same tissue components as the main spleen, including sinusoids, lymphoid follicles, and red pulp 4

Management

• Most accessory spleens require no treatment unless they are symptomatic 6
• Accessory splenectomy may be indicated in the following scenarios:
  • When identified during splenectomy for hematological diseases 2, 6
  • When symptomatic (causing pain or compression of adjacent structures) 6
  • When misdiagnosed as a tumor and surgical exploration is performed 3

Differentiation from Other Options

• Pseudocyst (option A): An acquired condition, not an embryological anomaly, usually resulting from trauma, infection, or pancreatitis 2
• Hypersplenism (option C): A functional disorder characterized by exaggerated splenic activity leading to peripheral cytopenia, not an embryological anomaly 2
• Splenomegaly (option D): An enlargement of the normal spleen due to various pathological conditions, not a developmental anomaly 2

Accessory spleens represent a normal variant of splenic development and are the most common congenital anomaly of the spleen, with significant clinical implications in certain scenarios despite their generally benign nature.