IMAGING ANATOMY OF THE LIVER FLIP OTTO DEPT. OF RADIOLOGY UNIVERSITAS ACADEMIC HOSPITAL 30 MARCH 2012

OVERVIEW Superficial anatomy Segmental liver anatomy Arterial blood supply Portal venous system Venous drainage Lymphatic drainage Radiological features

SUPERFICIAL ANATOMY AND RELATIONS

SEGMENTAL LIVER ANATOMY

Couinaud classification: Liver devided into 8 functionally independent segments, each with own vascular inflow, outflow and biliary drainage Triad of portal vein, hepatic artery and bile duct in centre Hepatic veins at periphery – intersegmental Middle hepatic vein devides into left and right lobes – Cantlie’s line Right hepatic vein devides right lobe into anterior and posterior segments Left hepatic vein devides left lobe into medial and lateral parts Portal vein devides liver into upper and lower segments

ARTERIAL BLOOD SUPPLY

VARIATIONS IN HEPATIC ARTERIAL ANATOMY Replaced common hepatic artery in 2.5% Replaced right hepatic artery in 10% Accessory right hepatic artery in 6% Left hepatic artery replaced by left gastric artery in 12% Accessory left hepatic arteries from left gastric artery in 13% Common hepatic artery may devide early or trifurcate with gastroduodenal artery Hepatic artery may arise seperately from aorta and not from the coeliac trunk

VARIATIONS IN HEPATIC ARTERIES

PORTAL VENOUS SYSTEM Portal vein forms posterior to neck of pancreas by union of SMV and splenic vein Anterior to IVC and posterior to bile duct and hepatic artery in free free edge of lesser omentum Devides into right and left portal veins at porta RPV devides into RAPV(segments V and VIII) and RPPV(segments VI and VII) Variations include trifurcation of PV into RAPV, RPPV and LPV; and RPPV as 1 st branch of PV

VENOUS DRAINAGE Hepatic veins drain upwards and backwards to IVC without an extrahepatic course Right, middle and left veins drain corresponding thirds of the liver MHV may unite with LHV and have common final course to IVC Smaller veins drain directly to IVC from lower parts of right and caudate lobes

RELATIONSHIP BETWEEN PORTAL AND SYSTEMIC VENOUS SYSTEMS

LYMPHATIC DRAINAGE Deep lymphatics drain in connective tissue along portal triads and along hepatic veins Lymphatics drain to nodes in porta hepatis, hepatic nodes along hepatic vessels and nodes in lesser omentum Via retropyloric nodes to coeliac nodes and cisterns chyli Superficial lymphatic network under liver capsule: Anterior parts of diaphragmatic and visceral surface drain to deep lymphatics Posterior parts drain to bare area and on to phrenic lymph nodes; or joins deep lymphatics running along hepatic veins towards IVC, draining into posterior mediastinal lymph nodes

RADIOLOGICAL FEATURES Imaging modalities CT MRI Ultrasound Hepatic angiography CT angioportography Portal venography Hepatic venography Hepatic scintigraphy

CT OF THE LIVER

Single phase (portal phase) contrast-enhanced CT Imaged at peak of parenchymal enhancement i.e. portal venous enhancement 60-70s after start of bolus injection Multi-phasic contrast-enhanced CT Most tumours receive blood supply from hepatic arteries, therefore enhancing strongly on arterial phase (20-25s after start of bolus) Early and late arterial phases, portovenous and delayed phases according to clinical indication

MRI OF THE LIVER

Liver parenchyma equal signal intensity to pancreas and higher on T1 and lower on T2 than the spleen Hepatic vessels seen as signal void on standard imaging Major hepatic veins and secondary branches of portal veins visible Hepatic arteries not well seen unless iv contrast given On T2 ligamentum venosum and ligamentum teres low intensity with high intensity fat within their fissures Common pulse sequences: T1-W GRE with or without fat suppression; T2-W FSE; heavily T2-weighted Contrast-enhanced MRI: Gd-enhanced T1-W; Liver specific contrast agents e.g. SPIO for RE cell imaging

ULTRASOUND OF THE LIVER

Liver particularly suited for ultrasound imaging Also used as acoustic window for viewing other structures: right kidney and adrenal gland, gallbladder and pancreas Vessels and bile ducts particularly well seen Blood flow studied using colour flow Doppler and direction and velocity of flow inn portal vein evaluated with pulsed wave Doppler US contrast media can help characterise lesions

HEPATIC ARTERIOGRAPHY

Catheter introduced into aorta and coeliac trunk via femoral puncture Greater selectivity if contrast injected distal to origin of gastroduadenal artery Frequency of normal variation may make injection of SMA and left gastric arteries also necessary MR and CT angiography can also produce excellent images of coeliac trunk and SMA

CT ANGIOPORTOGRAPHY Was more commonly performed pre-operatively before universal availability and improved capabilities of MRI to identify liver tumours or metastases in patients considered for resection CT performed 60s after selective injection of contrast into SMA; in portovenous phase Portal perfusion defects on CTAP in segments I, IV and around falciform ligament in 10% of patients due to non- portal venous inflow directly into subsegmental hepatic parenchyma

PORTAL VENOGRAPHY

Direct portography Splenoportography Transjugular transhepatic approach Transumbilical portography by catheterizing the umbilical vein Indirect portography Late phase superior mesenteric angiography

HEPATIC VENOGRAPHY

Acieved via the IVC usually by retrograde approach through internal jugular vein Catheterization of three main hepatic veins in turn May also achieve radiographically-directed hepatic venous pressure measurements or transjugular biopsy or TIPS

HEPATIC SCINTIGRAPHY Tc-99m colloid scintigraphy Taken up by phagocytosis by RE cells Rarely used to diagnose metastases or tumours, but helpful to identify benign focal nodular hyperplasia and to evaluate liver function e.g. liver cirrhosis Tc-99m IDA scintigraphy Excreted by hepatocytes into bile, allowing assessment of biliary drainage and gallbladder function Tc-99m labelled RBC imaging Highly specific for diagnosing cavernous haemangioma F-18 FDG PET and In-111 Octreotide in oncological imaging

REFERENCES Aitchison, F. (2009) A Guide to Radiological Procedures. 5 th ed. London: Saunders Elsevier. Butler, P., Mitchell, A.W.M. & Ellis, H. (1999) Applied Radiological Anatomy. Cambridge: Cambridge University Press. Ryan, S., McNicholas, M. & Eustace, S. (2011) Anatomy for Diagnostic Imaging. 3 rd ed. London: Saunders Elsevier.