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Background
Lysosomal storage disorders (LSDs) include all the subtypes of mucopolysaccharidosis (MPS), mucolipidosis, Pompe’s disease (glycogen, storage disorder II), cystinosis, Gaucher’s disease, Niemann Pick disease (NPD), Wolman disease, metachromatic leukodystrophy, neuronal ceroid lipofuscinosis (NCL) and Fabry’s disease, among others. These disorders affect more than one organ system, as the abnormal metabolite may accumulate anywhere in the body. Most LSDs share imaging features owing to a shared predilection for certain organ systems in the body, such as visceromegaly, cardiac valvular abnormalities, and central nervous system (CNS). Thus, the choice of imaging modality depends on the organ system involved.

Educational Goals / Teaching Points
LSDs encompass a large group of genetic abnormalities of metabolism leading to the accumulation of various intracellular metabolites. They are further classified based on the kind of metabolite accumulating within the cell which may be mucopolysaccharides, glycoproteins, amino acids or lipids. A large majority of these disorders present in infancy or early childhood and can have debilitating effects if left untreated, mandating early diagnosis. Through this exhibit, we aim to describe the pathophysiology and imaging features of various LSDs. We will also provide a comprehensive overview of features that are common to most of them as well as illustrate the differentiating features unique to some of them.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Radiographs play a crucial role in performing skeletal surveys in these patients as most of them share a spectrum of skeletal manifestations collectively termed "dysostosis multiplex". Patients of cystinosis may show metaphyseal abnormalities consistent with rickets. Ultrasonography (US) is used to evaluate visceromegaly and the varying appearance of hepatic nodules and splenic masses in patients with Gaucher disease or NPD. Magnetic resonance imaging (MRI) is the preferred modality for visceral volumetry. It is also vital to study CNS manifestations and bone marrow involvement in these patients. Certain imaging and clinical features are characteristic, such as enlarged and calcified adrenal glands in Wolman disease; cardiomegaly, hypertrophic cardiomyopathy, fatty replacement of muscles and an absence of dysostosis multiplex in Pompe’s disease; proximal tubular dysfunction with consequent hypophosphatemic rickets and medullary nephrocalcinosis in the infantile form of cystinosis; hepatosplenomegaly, bone marrow signal abnormalities, H-shaped vertebrae, Erlenmeyer flask deformity, and anemia in Gaucher disease; and cherry red maculae with delayed skeletal maturation and visceromegaly in NPD.

Conclusion
In view of the availability of enzyme replacement therapy for a few of these LSDs, it is prudent to diagnose these patients at the earliest to prevent an untimely death. Thus, the radiologist must be familiar with the various clinical and imaging manifestations of these disorders to aid in management.