From the Guidelines
Transient hepatic attenuation difference (THAD) is a radiological finding that requires further investigation to determine its underlying cause, which may be a benign physiological variant or a serious pathology requiring treatment. This phenomenon occurs due to altered blood flow dynamics within the liver, resulting from increased arterial blood supply to a specific liver region, often compensating for reduced portal venous flow 1. Common causes of THAD include portal vein thrombosis, liver tumors (both benign and malignant), inflammatory conditions, cirrhosis, and vascular abnormalities.
When a THAD is identified, additional imaging studies such as multiphasic CT, MRI with contrast, or ultrasound with Doppler are necessary to determine the cause 1. The clinical significance of a THAD depends entirely on its underlying cause, and management focuses on addressing the underlying condition rather than the THAD itself. Some possible underlying conditions that may cause THAD include nonalcoholic fatty liver disease (NAFLD), alcohol-induced liver disease, and other causes of fatty liver disease 1.
Key points to consider when evaluating THAD include:
- The need for further investigation to determine the underlying cause
- The potential for THAD to represent a benign physiological variant or a serious pathology requiring treatment
- The importance of addressing the underlying condition rather than the THAD itself
- The use of additional imaging studies to determine the cause of THAD
In terms of imaging modalities, abdominal ultrasonography is the first-line imaging modality for screening asymptomatic patients with abnormal liver enzyme levels, but it has limitations in terms of sensitivity and specificity 1. Other imaging modalities such as CT and MRI may be used to further evaluate THAD and determine its underlying cause. Controlled attenuation parameter (CAP) is a feature of transient elastography that can quantify the degree of fat deposition in the liver parenchyma, and may be useful in evaluating patients with THAD 1.
From the Research
Definition and Characteristics of Transient Hepatic Attenuation Difference (THAD)
- Transient hepatic attenuation difference (THAD) is a perfusion disorder that can be observed in the hepatic arterial phase of a biphasic spiral CT examination 2
- THAD appears as an area of high attenuation on the hepatic arterial phase image and returns to normal attenuation on the portal venous phase image 2
- The knowledge of the shape, distribution, and causes of THAD is essential to differentiate THAD from other pathologies such as neoplasm 3, 2
Causes and Associations of THAD
- THAD can be associated with various causes, including chronic cholecystitis, previous biliary surgery, Budd-Chiari syndrome, portal venous thrombosis, liver cirrhosis, acute inflammation of an adjacent organ, and others 3, 4
- THAD can also be related to focal liver lesions, particularly hypervascular lesions, due to primary arterial hyperperfusion 5
- In some cases, THAD may not be connected to focal lesions, and its causes can be classified into four groups: portal vein stoppage-obstruction, portal in-flow diversion, trauma, and inflammation 4
Clinical Significance and Prognosis of THAD
- THAD can be a valuable finding in detecting hypervascular lesions and evaluating the severity and prognosis of liver diseases, such as drug-induced liver injury 6
- The presence of THAD, along with other MRI features like irregularity of the liver surface and splenomegaly, can be independently associated with the severity of liver injury 6
- THAD and ascites may have potential clinical utility in predicting liver transplantation/liver-related death outcomes within 1 year 6