The Thymus: to Remove or Not to Remove? That is the Question.

Why do I ask?

I believe it's very relevant to a parent of a child with Hypoplastic Left Heart Syndrome who has had surgical repair, because in order to access the heart, a surgeon must remove the thymus located above it.

What is the thymus?

The thymus gland is an organ of the immune system. The thymus gland is located in the upper part of the chest cavity, directly behind the sternum. It is largest in size in childhood, about the size of an apple, continues to grow throughout puberty, and slowly shrinks in size into adulthood, to the size of a pea.

                                

What does the thymus do?

The role of the thymus gland is to process lymphocytes, which are white blood cells that travel the body through the bloodstream. These lymphocytes, also called T-lymphocytes or T-cells, protect the immune system by blocking the invasion of viruses and bacteria. They also help to prevent abnormal cell growth that occurs with cancer.

What we don't know.

If the thymus gland is removed in infancy, the immune system may never fully develop. Does this increase the chance of infection in children who have no thymus gland or whose thymus never developed properly, because the majority of t-cell production occurs early in life?

What we do know.

Ancient Greeks believed the thymus to be the seat of the soul, but for centuries its significance remained unremarkable. It wasn't until 1961 when Dr. Jacques Miller, a French-Australian immunologist, solved an ancient medical mystery and proved an unbelievable result…the thymus was of crucial importance to the immune system.

A 1982 article in The New York Times discusses aging and the gradual decline in immune function, demonstrating the importance of the thymus gland in function and protection of the immune system. Many studies since the initial finding of Miller in 1961 have supported the importance of thymus related to asthma, allergy, dermatitis, rheumatoid arthritis, autoimmune disease and cancer.

What does this mean to a child with HLHS?

Are children who have had their thymus removed potentially becoming immunodeficient?  Many doctors do not believe there is an increased risk of infection in children who have had their thymus removed. Does the medical community underestimate the important immunity function of the thymus gland? Research experiments in the 1960's proved it was a necessary organ, and current research studies are being conducted to understand the relationship of thymus gland function and immunity.

Examples of current research.

In 2004, researchers at Children's Hospital Iceland, Reykjavik, published "The influence of partial or total thymectomy during open heart surgery ininfants on the immune function later in life," which describes their findings from a 10-year study conducted on nineteen children who underwent open heart surgery compared to nineteen healthy controls of the same age and gender. Each subject's blood was tested at age ten.  The study group had lower counts for lymphocytes (part of the white blood cell that recognizes a foreign substance) and higher counts for neutrophils (part of the white blood cells that respond to infection) compared to the control group confirming lower t-cell production, but did not demonstrate clinical significance early in life.

Similar studies with similar findings.

Immunodeficiency following neonatal thymectomy in man

Levelsof Recent Thymic Emigrant Cells Decrease in Children Undergoing Partial Thymectomy during Cardiac Surgery

Thymic Function and Impaired Maintenance of Peripheral T Cell Populations in Children with Congenital Heart Disease and Surgical Thymectomy

Complete DiGeorge syndrome: Development of rash, lymphadenopathy, and oligoclonal T cells in 5 cases

Longitudinal analysis of immune function in the first 3 years of life in thymectomizedneonates during cardiac surgery

For neonates undergoing cardiac surgery does thymectomy as opposed to thymic preservation have any adverse immunological consequences?

Where do we go from here?

In 2002, a Monash University researcher presented a very interesting finding in the study, "Regrowing the Thymus Gland," in which he describes the successful regrowth of the thymus back to full size in mice, to begin producing t-cells again to strengthen the immune system. Barring the regrowth of the thymus gland, strengthening the immune system today can be approached in several ways. Proper nutrition in the form of a well balanced diet and antioxidants is one approach. Sweetbreads, made from the thymus glands of young calves, like many organ meats, are a nutritional powerhouse packed with vitamins, minerals, amino acids and other substances vital for nutrition. Although not well studied in humans, supplementing a diet with the thymus gland extract is said to boost the immune system. Thymic hormone replacement therapy, although unapproved and unregulated by the FDA, has demonstrated some potential benefits clinically, with the regular use of thymus therapy.

We simply need more research. Thymus re-implantation in the future? Seems like an inevitable course. 

Author's Note:  My son was diagnosed at 18 months of age with Common Variable Immune Deficiency, a primary immune deficiency.  For more information about primary immune deficiencies, please visit The Immune Deficiency Foundation.