Zebra spleen, also referred to as psychedelic spleen, tigroid splenic enhancement or more correctly inhomogeneous splenic enhancement, refers to the transient heterogeneous parenchymal enhancement of the spleen during the arterial or early portal venous phases of contrast enhancement in CT, MRI, or ultrasound imaging. The spleen is normally homogenous without contrast enhancement, with attenuation values between 40-60 Hounsfield Units ⁵.

It is due to the differing flow rates of blood (and contrast) between red pulp (which enhances early) and white pulp (which enhances later). Almost always, a portal venous or delayed phase study will show homogeneous attenuation throughout the spleen (in the absence of pathology).

There are 3 general patterns of enhancement ²:

archiform: alternating bands of low and high density which may look like rings or zebra stripes
focal: single area of low density
diffuse: mottled appearance

These three different patterns are primarily due to splenic enlargement, age of the patient and contrast injection rate ⁴.

Heterogeneity of splenic parenchyma manifested as alternating hypoechoic stripes can also be seen in non-contrast ultrasound examination of spleen with high-frequency linear transducer in children with no underlying splenic abnormalities; this has been assumed to be due to the difference in splenic parenchymal structures ¹.