Imaging of THID and THAD

1. Imaging of THID and THAD SN Gandhi, DA Aguirre, JG Wong, AC Santosa, JM Pereira De Jesus, CS Sirlin

2. DEFINITIONS • THID • Transient hepatic intensity difference • Magnetic resonance (MR) imaging • THAD • Transient hepatic attenuation difference • Computed tomography (CT)

3. OBJECTIVESImaging of THID and THAD Goals of this exhibit: • Review the mechanisms through which THID and THAD occur. • Recognize the various imaging appearances of THID and THAD through multiple examples. • Review the diagnostic importance of THID and THAD.

4. INTRODUCTION • THID and THAD describe the imaging appearances of perfusion abnormalities in the liver. • These classically manifest during the hepatic arterial phase (HAP), and revert to normal during the portal venous phase (PVP). • However, depending on the size of the abnormality, persistence of THID/THAD during the PVP is relatively common. • Variety of imaging appearances: • Wedge-shaped, peripheral • Lobar/segmental • Circumferential • Mosaic • Recall the dual blood supply of the liver • Portal vein – 75% • Hepatic artery – 25%

5. DUAL BLOOD SUPPLY • Pre • PV flow – 75% • HA flow – 25% • Early HAP • HA fully enhanced • Minimal liver enhancement • Late HAP • PV begins to enhance • Mild liver enhancement • PVP • PV fully enhanced • Maximal liver enhancement • EqP • Equilibration of contrast • Arteries • Veins • Parenchyma HA PV

6. NORMAL LIVER PERFUSIONCT Pre HAP PVP Normal liver perfusion shown before contrast and during the HAP and PVP.

7. NORMAL LIVER PERFUSIONBolus Tracking CT Kinetics of liver perfusion: Precontrast through PVP

8. MECHANISMSMajor Categories INFLOW • Decreased Portal Venous Flow • Arterioportal Shunt • Increased Arterial Flow • Decreased Arterial Flow OUTFLOW • Decreased Hepatic Venous Flow OTHER • Variant Anatomy • Miscellaneous

9. ↓ PORTAL VENOUS FLOWCauses Causes of ↓ PV flow • Portal vein obstruction • Thrombosis • Multiple etiologies • Consider septic thrombosis (pylephlebitis) • Invasion • Hepatocellular carcinoma (HCC) • Cholangiocarcinoma • Compression • Tumor • Infection • Surgical ligation • Biliary obstruction • Large THID/THAD due to biliary obstruction is uncommon. • Hepatic parenchymal compression

10. PHYSIOLOGY • Portal vein obstruction: Two mechanisms • Increased arterial flow compensates for the absence or reduction of portal venous flow. • Reduced dilution of arterial contrast agent by unopacified portal venous blood increases relative contrast delivery during arterial phase. • Biliary obstruction: • Uncertain mechanism, but biliary obstruction may result in decreased portal venous flow through obstruction of the peribiliary plexus.

11. PORTAL VEIN OBSTRUCTIONPV thrombosis PV thrombosis HAP Lobar/segmental distribution secondary to thrombosis of the left portal vein ↓ PORTAL VENOUS FLOW

12. PORTAL VEIN OBSTRUCTIONPylephlebitis Diverticulitis PV thrombus HAP Septic thrombosis, due to seed of portal veins from abdominal infection ↓ PORTAL VENOUS FLOW

13. BILIARY OBSTRUCTIONAmpullary carcinoma CT HAP Wedge-shaped distribution of THAD in the setting of biliary obstruction is uncommon. Peribiliary enhancement is more commonly observed. ↓ PORTAL VENOUS FLOW

14. PARENCHYMAL COMPRESSIONSubcapsular Hematoma CT PVP HAP Note peripheral THAD (arrows) which is absent on PVP imaging. Reduction of PV flow likely due to low pressure of the PV system relative to the HA system. ↓ PORTAL VENOUS FLOW

15. ARTERIOPORTAL SHUNTINGCauses Causes of arterioportal shunting • Cirrhosis • Iatrogenic • Biopsy-related AV fistula • Tumor • Most commonly HCC • Trauma

16. CIRRHOSISPeripheral THID distribution T1w dynamic GRE HAP Multiple small peripheral AV shunts (arrows) ARTERIOPORTAL SHUNT

17. CIRRHOSISSegmental THID/THAD Distribution CT T1w dynamic GRE HAP HAP Lobar/segmental distribution (arrows). Note portal vein enhancement during arterial phase. ARTERIOPORTAL SHUNT

18. IATROGENICAV fistula s/p biopsy CT – adjacent images HAP Peripheral wedge-shaped distribution ARTERIOPORTAL SHUNT

19. TUMORLiver Metastasis T1w dynamic GRE HAP Tumor Peripheral wedge-shaped distribution ARTERIOPORTAL SHUNT

20. TUMORTHAD later reveals HCC CT HAP HAP HCC THAD 3 months later ARTERIOPORTAL SHUNT

21. TUMORFlash-fill hemangioma CT – adjacent images Hemangioma HAP Peripheral wedge-shaped distribution (arrowhead) ARTERIOPORTAL SHUNT

22. ↑ Hepatic Arterial FlowCauses Causes of ↑ HA flow • Tumor • Essentially all liver tumors are fed by the hepatic artery. Some are “hypervascular” and some “hypovascular,” but the increased arterial flow to the tumor may result in increased arterial flow to the surrounding hepatic parenchyma. • “Steal” phenomenon • Inflammation • Cholecystitis • Abscess

23. TUMORMelanoma Metastases CT “Steal” phenomenon HAP Lobar/segmental distribution of increased arterial flow surrounding two cystic melanoma metastases ↑ ARTERIAL FLOW

24. TUMORNon-Hodgkin Lymphoma CT “Steal” phenomenon HAP Circumferential pattern of increased arterial flow surrounding lymphoma (arrows) ↑ ARTERIAL FLOW

25. INFLAMMATIONLiver Abscess CT “Steal” phenomenon HAP Circumferential pattern of increased arterial flow surrounding abscess (arrows) ↑ ARTERIAL FLOW

26. INFLAMMATIONCholecystitis CT PVP PVP THAD present primarily in hepatic parenchyma surrounding gallbladder fossa. Note that conspicuity of the THAD in this case is reduced, likely related to PVP imaging. ↑ ARTERIAL FLOW

27. ↓ Hepatic Arterial FlowCauses Causes of ↓ HA flow • Iatrogenic (e.g. following liver transplant) • Surgical ligation • Thrombosis • Atherosclerosis • Embolic phenomena • Vasculitis

28. IATROGENICs/p Transplant T1w coronal dynamic GRE HAP HAP Note the “split” appearance of liver perfusion due to decreased HA and PV flow, due to surgical ligation or thrombosis resulting in infarct. ↓ ARTERIAL FLOW

29. ↓ HEPATIC VENOUS FLOWCauses Causes of ↓ HV flow • Right-sided heart failure • Pericardial disease • Budd-Chiari syndrome

30. RIGHT HEART FAILURE CT HAP Mosaic pattern created by diffuse perfusion abnormalities ↓ HEPATIC VENOUS FLOW

31. OTHER CAUSES OF THID/THAD Additional causes • Variant anatomy • Aberrant arterial inflow • Collateral vessels • Superior vena cava (SVC) syndrome • Accessory veins • Capsular veins • Accessory cystic vein • Aberrant right gastric vein • Miscellaneous • Many additional causes, of unknown precise etiology • Example: radiation therapy

32. VARIANT ANATOMYSVC Syndrome (Histoplasmosis) CT Collateral vessels HAP THAD in the region of the falciform ligament (common location). Collateral vessels bypass the obstructed SVC via the umbilical vein to the left portal vein. OTHER CAUSES OF THID/THAD

33. MISCELLANEOUSRadiation Therapy CT HAP PVP Note the linear THAD (arrows) corresponding to shape of radiation portal.

34. IMPORTANCE OF THID/THAD How THID and THAD can be helpful • First observation of a significant abnormality • Example shown in exhibit: • HCC preceded by 3 months with a THAD • Iatrogenic AV fistula • Better describe an abnormality • Examples shown in exhibit: • Septic thrombosis of portal venous branches due to diverticulitis, underscoring the severity of the disease process • THAD due to SVC syndrome

35. PITFALLS Avoid the following: • Mistaking THID or THAD for neoplasm. • Inclusion of the THID or THAD in measurement of lesion size.

36. SUMMARYMechanisms for THID and THAD

37. REFERENCES • Quiroga S, et al. “Improved Diagnosis of Hepatic Perfusion Disorders: Value of Hepatic Arterial Phase Imaging during Helical CT.” RadioGraphics 2001; 21: 65-81. • Colagrande S, et al. “Transient Hepatic Attenuation Differences.” AJR 2004; 183: 459-464. • Chen W, et al. “Spectrum of Transient Hepatic Attenuation Differences in Biphasic Helical CT.” AJR 1999; 172:419-422. • Itai Y, Matsui O. “Blood Flow and Liver Imaging.” Radiology 1997; 202: 306-314. • Choi SH, et al. “Relationship Between Various Patterns of Transient Increased Hepatic Attenuation on CT and Portal Vein Thrombosis Related to Acute Cholecystitis.” AJR 2004; 183: 437-442. • Urban B, McGhie P, Fishman E. “Helical CT: Diagnostic Pitfalls of Arterial Phase Imaging of the Upper Abdomen.” AJR 2000; 174: 455-461.

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