An infant is born with facial dysmorphia and a cleft palate. Further evaluation reveals a heart condition with a right-to-left shunt and the absence of a thymic shadow on x-ray. The infant experiences frequent and recurrent sinopulmonary infections. Examination of this patient's lymph nodes will most likely show poor development of which of the following structures?

Question

An infant is born with facial dysmorphia and a cleft palate.  Further evaluation reveals a heart condition with a right-to-left shunt and the absence of a thymic shadow on x-ray.  The infant experiences frequent and recurrent sinopulmonary infections.  Examination of this patient's lymph nodes will most likely show poor development of which of the following structures?

Quizplus · Accepted Answer

11ec160b_3a71_a3a9_9249_514f906a7844_MD0001_00 DiGeorge syndrome is caused by maldevelopment of the third and fourth pharyngeal pouch derivatives. Immunodeficiency can result from thymic aplasia, which leads to an extreme deficiency in the number of mature T lymphocytes. Although T cells are synthesized in the bone marrow, they require processing in the thymus in order to mature and mount effective immune responses. Patients are thus predisposed to recurrent infections by viral, fungal, protozoan, and intracellular bacterial pathogens. The paracortex is the region of the lymph node populated primarily by T lymphocytes and dendritic cells. It lies internal to the cortex, between the follicles and medulla. Dendritic cells present antigens that they collect from the blood and lymph to the aggregated T lymphocytes in this region. The paracortex becomes enlarged by the proliferation of T lymphocytes during adaptive cellular immune responses (eg, viral infections). In DiGeorge syndrome, this region is poorly developed due to a deficiency of mature T lymphocytes. (Choice A) Located in the outer cortex, the follicles are sites of B lymphocyte localization and proliferation. Primary follicles are dense and dormant; secondary follicles have a pale germinal center containing proliferating B cells and follicular dendritic cells. In agammaglobulinemia, germinal centers and primary lymphoid follicles do not form due to an absence of B cells. (Choices B and C) The medulla of the lymph node consists of medullary cords and sinuses. The medullary cords contain B cells, plasma cells, and macrophages, and the medullary sinuses contain reticular cells and macrophages. (Choice E) The subcapsular sinuses are the regions lying between the capsule and cortex of the lymph node. They are in direct communication with afferent lymphatic vessels and the cortical sinuses that line the trabecula. The cortical sinuses are continuous with the medullary sinuses and the single efferent lymphatic channel exiting the hilum. Educational objective: DiGeorge syndrome causes an extreme deficiency in the number of mature T lymphocytes, leading to poor development of the lymph node paracortex. In contrast, agammaglobulinemia causes an absence of B cells, preventing primary lymphoid follicles and germinal centers from forming in the lymph node cortex.

An Infant Is Born with Facial Dysmorphia and a Cleft