Acute Thymic Involution
Jessica M. Comstock, MD
Key Facts
Terminology
Incidental thymic involution caused by endogenous steroid release in response to various stressful situations
Etiology/Pathogenesis
Numerous stressors including infection, chronic disease, malnutrition, and corticosteroid use
Microscopic Pathology
Grade correlates with duration and severity of illness
Top Differential Diagnoses
Thymic dysplasia
Physiologic involution
 This thymus at low power shows the classic “starry sky” appearance of acute thymic involution. The dense blue cortex (the sky) is punctuated by macrophages (the stars). |
 The “starry sky” appearance of acute thymic involution is caused by macrophages ingesting lymphocytes (lymphophagocytosis  ). This process is caused by endogenous steroid release due to stress. |
TERMINOLOGY
Synonyms
Thymic atrophy
Acquired hypoplasia
Definitions
Incidental thymic involution caused by endogenous steroid release in response to various stressful situations
ETIOLOGY/PATHOGENESIS
Environmental Exposure
Malnutrition
Prolonged physical or emotional stress
Chronic disease
Infectious Agents
Viral infections, especially HIV
Bacterial infections
Fungal infections
Chorioamnionitis
Treatment Related
Acute and chronic GVHD
Chemotherapy
Irradiation
Prolonged treatment with corticosteroids
CLINICAL ISSUES
Epidemiology
Age
All ages, including fetal
