Purpose or Case Report: Recent literature has illuminated increasing diagnostic uses of arterial spin labeling (ASL). This MR technique obtains accurate and reliable CBF measurements non-invasively and can be performed multiple times during the same exam, unlike other perfusion techniques.

A wide variety of entities, including normal variants, pathological conditions, and technical errors can demonstrate abnormal CBF values.

This Educational Exhibit has three main purposes:

1. To classify the main abnormal ASL perfusion patterns in the pediatric brain.

2. To discuss the potential clinical significance of abnormal ASL values.

3. To discuss the utility of this technique in the pediatric clinical setting.
Methods & Materials: For the purpose of this study, perfusion abnormalities were divided into three main categories: patterns with increased brain perfusion, decreased perfusion and mixed. Subsequently the two first categories were divided into two subcategories: focal or diffuse.

A review of our RIS database was performed looking for cases which might better illustrate the abovementioned different categories of perfusion abnormalities.
Results: We gathered a group of illustrative cases with different abnormal perfusion patterns, and subsequently classified them in the following manner:

I. Increased perfusion

I.a. Diffuse
I.a.1. Post profound anoxic injury
I.a.2. Sickle cell anemia
I.a.3. Meningoencephalitis
I.a.4. Post generalized seizure

I.b. Focal
I.b.1. Luxury perfusion post infarct
I.b.2. Hypoxic ischemic encephalopathy of the newborn
I.b.3. Herpes encephalitis
I.b.4. Focal seizure (ictal phase)

II. Decreased perfusion

II.a. Diffuse
II.a.1. Moya-Moya disease
II.a.2. Menkes syndrome
II.a.3. Craniosynostosis

II.b. Focal
II.b.1 Low grade neuroepithelial tumor
II.b.2. PRES
II.b.3. Seizure (interictal phase)
II.b.4. Artifactual: tilted position of the head
II.b.5. Subdural hematoma

III Mixed increased and decreased perfusion

III.a Concomitant sickle cell and Moyamoya
III.b. Dyke Davidoff Masson syndrome with contralateral hyperperfusion
III.c. Ruptured MCA aneurysm with simultaneous MCA infaract
III.d. Sickle cell with hyperperfusion, status post EDAS
Conclusions: Arterial spin labelling (ASL) is a robust, non invasive technique that can be used to characterize and measure cerebral perfusion. It has become increasingly available in routine clinical practice and radiologists should be comfortable with its interpretation. This exhibit depicts various processes that may alter the appearance of ASL images in characteristic patterns and enhance diagnostic yield.