SN5
SHORT NOTE
5M
★ High-yield
Describe the fate of the vitelline duct. Write in detail on Meckel diverticulum.
The Vitelline Duct
The vitelline (omphalomesenteric) duct connects the midgut to the yolk sac, and normally becomes obliterated and disappears by the 7th week.
| Persistence of | Result |
|---|---|
| Proximal part | MECKEL diverticulum |
| Whole duct | Umbilical (faecal) fistula — discharges intestinal content at the umbilicus |
| Distal part | Umbilical sinus |
| Central part only | Vitelline cyst (enterocystoma) between two fibrous bands |
| Fibrous cord alone | A band from the ileum to the umbilicus — a cause of volvulus and internal herniation |
Meckel Diverticulum
- The commonest congenital anomaly of the gastrointestinal tract
- A true diverticulum — it contains all layers of the bowel wall
- Arises from the antimesenteric border of the ileum — unlike an acquired diverticulum, which is mesenteric
- Has its own blood supply, a persistent vitelline artery
- Present in about 2% of the population
- About 2 feet (60 cm) proximal to the ileocaecal valve
- About 2 inches (5 cm) long
- 2 types of ectopic tissue — gastric and pancreatic
- Commonly symptomatic before the age of 2 years
- About 2% of those with one ever develop symptoms; male : female about 2 : 1
Clinical Presentations
| Presentation | Mechanism | Age |
|---|---|---|
| Painless rectal bleeding | Peptic ulceration of adjacent ileum by ectopic gastric mucosa | The commonest presentation in children |
| Intestinal obstruction | Volvulus round a fibrous band, intussusception with the diverticulum as the lead point, or a hernia | The commonest presentation in adults |
| Diverticulitis | Inflammation, sometimes with perforation | Clinically indistinguishable from appendicitis |
| Umbilical discharge | Patent duct | Neonate |
| Littre hernia | The diverticulum is the content of a hernial sac | Any age |
- If the appendix looks normal at operation for suspected appendicitis, the terminal ileum must be examined for a Meckel diverticulum — a rule that is regularly examined and regularly forgotten
Applied Aspects
- Technetium-99m pertechnetate ("Meckel") scan is the investigation of choice, with a sensitivity of about 85% in children, less in adults
- Symptomatic diverticula are excised; a broad-based one requires segmental resection to remove all the ectopic mucosa
- An incidentally found diverticulum in an adult is usually left alone, since the lifetime risk of complication is low and falls with age; in a child it is often removed
- Consider it in any child with painless rectal bleeding — the differential includes intussusception, polyp and anal fissure, but a Meckel diverticulum bleeds briskly and painlessly
All questions in Systemic Embryology
- Q1Describe the development of the heart. Explain the septation of the atria and ventricles and add a note on the congenital anomalies. ★
- Q2Describe the pharyngeal arches with their nerves, muscles and skeletal derivatives. Describe the derivatives of the pharyngeal pouches. ★
- Q3Describe the development of the gastrointestinal tract. Explain the rotation of the midgut and add a note on its anomalies. ★
- Q4Describe the development of the kidney and the urinary bladder. Add a note on the development of the genital ducts. ★
- Q5Describe the development of the face and the palate. Add a note on cleft lip and cleft palate. ★
- SN1Describe the fetal circulation and the changes that occur at birth. ★
- SN2Describe the development of the diaphragm. Add a note on congenital diaphragmatic hernia. ★
- SN3Describe the development of the thyroid gland. Add a note on thyroglossal cyst and ectopic thyroid. ★
- SN4Describe the development of the lungs and the body cavities. ★
- SN5Describe the fate of the vitelline duct. Write in detail on Meckel diverticulum. ★
- SN6Describe the descent of the testis. Add a note on undescended testis and the anomalies of the processus vaginalis. ★
- SN7Describe the development of the vertebral column and the limbs.