Central Conducting Lymphatic Abnormalities in Noonan Syndrome Identified Using SPECT/CT Lymphoscintigraphy

Noonan syndrome (NS) is a pleiotropic autosomal dominant RAS/MAPK pathway disorder affecting 1 in 1000–2500 live births [1] [2] [3]. Cardinal features include a characteristic facial appearance, short stature, congenital heart disease, and developmental delay [1] [2]. Pathogenic variants in genes such as PTPN11, SOS1, and KRAS cause RAS/MAPK pathway dysregulation, classifying NS as a "RASopathy" [4] [5]. Lymphatic abnormalities, including peripheral oedema, protein-losing enteropathy, or chylothorax, affect approximately 20% of patients and are often due to central conducting lymphatic abnormalities (CCLA) [3] [6]. To our knowledge, no previous reports have documented CCLA in NS using single-photon emission computed tomography (SPECT)/computed tomography (CT) fusion lymphoscintigraphy. We report a young adult with NS whose sequential fluoroscopic lymphangiography, CT, and lymphoscintigraphy findings confirmed CCLA.