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Description : Radiological anatomy - Liver by Dr Ashenafi

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Published on : Oct 30, 2021 | Views : 3931 | Downloads : 21

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Liver Anatomy & Examination Techniques Aug,2021 by Ashenafi A Buser (MD) Assistant professor of Radiology (Subsp in BI, Interventional R) Department of Radiology & MRT SPHMMC
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Outline Structure & Vascular supply Morphological anatomy Functional Anatomy Examination techniques & appearance of normal liver : Ultrasonography, Computed tomography, Catheter assisted hepatic CT, MRI & Angiography
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Grossly Largest/heaviest solid organ (1.5kg) Rt hypochondrium to Lt of midline Relations: Anterior: Posterior:
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Structure Cellular level : hepatocytes (metabolic : exo and endocrine fn) & Kupffer cells (RES – lymphoid ) Subsegmentally: lobules each: central vein surrounded by sinusoids peripherally bounded by portal tracts, triad of br’s from bile duct, portal vein & hepatic artery
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Image
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Gross Anatomy: described - external appearance (- morphological) or - internal vascular structures (- functional)
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External landmarks GB & IVC Peritoneal ligaments: B/se developed in the ventral Mesentery superior & visceral surfaces Falciform ligament: - peritoneum umbilicus to the liver - free edge : ligamentum teres (Round lig) *fissure for ligamentum teres Peritoneal folds of lesser omentum *Fissure for Ligamentum venosum:
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Morphological Anatomy: ext appearance - Lobes: part of a parenchyma limited by fissures or grooves - two main lobes (Rt & Lt) and two accessory lobes (quadrate & caudate)
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Rt lobe : Rt of invisible line between IVC & GB / Falciform Lig Lt lobe: Lt of falciform lig & fissure for lig teres, anterior to fissure for lig venosum Caudate lobe: ant by fiss for Lig Venosum & post by IVC Quadrate lobe: Rt - GB fossa, Lt - falciform lig & postly porta hepatis
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Functional anatomy (segmental anatomy) - replaced morphological anatomy - built on scaffolding of hepatic veins & portal circulation (internal landmarks) exception Segment I. Blood supply: dual, hepatic artery & portal vein B. Drainage: hepatic veins
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(Proper)Hepatic artery: - 15% - br of CHA , Coeliac trunk - free edge of lesser omentum - divides into Rt & Lt branches at Porta Hepatis; 90% RHA anterior to PV - Variants: Replaced aa Accessory aa **From SMA: 18.5% - Rt HA: 16% from SMA : 10% replaced, 6% Accessory - CHA: 2.5% replaced CHA – from SMA **From LGA: 25% - Lt HA: 25% from Lt Gastric A: 13% accessory, 12% replaced
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Portal vein - 85% (Clinical signif ------ ); from Spl v & SMV @ L1/L2 ---gastric, cystic - free edge of lesser omentum - variations: 20-30% * trifurcation * Rt segmentals: independently from the main or from the Lt
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Hepatic veins - Unite to drain into IVC @ T9 - Caudate lobe into IVC - Variations : 70% 3 vv 30% acc vv (19% 2 Lt, 8% 2Rt, 2% 2 mi)
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Functional Anatomy (Segmental Anatomy)- - based on works of multiple investigators including Goldsmith & Woodburne, Couinaud & Bismuth.
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Three hepatic veins – liver – 4 sectors, each supplied by one of the four main portal venous br’s. - Rt : anterior & posterior - Lt : anterior (medial) & posterior (lateral) Portal scissurae – planes containing the hepatic veins
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Main portal scisurra/chief fissure, Cantlie’s line/ - traverses the liver from middle of the GB fossa anteriorly to the IVC posteriorly, specifically following the plane of mhv - separates it into two uneven hemilivers ess lobes Rt & Lt portal scissurae – planes of Rt & Lt hepatic vv Transverse scissura - defined by plane of Rt & Lt portal veins - divides the liver into sup & inf segments
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Rt lobe Rt main portal vein : 1 cm long ant to Caudate L - divides into ant & posterior br Anterior: ascending(sup)- seg 8 descending (inf)- seg 5 Posterior: superior br – seg 7 inferior br – seg 6
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Lt main portal v: 4cm in Lt lobe before bifurcating into superior & inf br’s in seg 4. in its course : caudate br’s, joined by round lig & gives off laterally Seg 2 & Seg 3 br’s
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Three hepatic veins: most cranial aspect of liver. - Rt: largest, drains most of the Rt lobe, complete seg, 6 & 7 and part of 5 & 8. defines the anatomic plane of Rt hepatic scissura. - Middle: superficially by chief fissure & drains seg 4, 5 & 8. 90% with Lt, 10% with alone into IVC. - Lt : shortest, drains seg 2,3 & dorsal seg 4 ----- liver adjacent to the veins are relatively avascular –better for surgical dissection.
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Rt lobe: Anatomical location Rt hepatic vein: runs in a plane almost coronal to the body, dividing the lobe into posteromedial & anterolateral sectors. With the axial plane, by Rt portal vein, 4 segments are defined: seg 5 (anterolateral - inferior), seg 6 (posteromedial - inferior), seg 7 (posteromedial - superior) & seg 8 (anterolateral - superior).
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Lt lobe: divided by Lt portal scissura into anterior & posterior sectors. Posterior (Lt side) - Segment 2 Anterior- Seg 3 & 4 Seg 4 – ant to Lt portal scissura & to the Lt of main portal scissura Seg 3 – Ant to Lt PS & post to Umb fissure - Segments 4 & 3 separated by Umb fiss: 4 being anteromedial and 3 posterolat. * Seg 4 – traditionally Quadrate lobe - Axial plane of Lt portal vein ---- 4a sup & 4b Inf * Some anatomists consider Seg 4 & 3 as one seg separated by portal pedicle
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Caudate lobe: seg 1, - functionally independent, receives from both Rt & Lt portal vv and drains into the IVC.
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Correlation with classic radiologic classification Rt anterior - superior – seg 8 & inferior – seg 5 Rt posterior – superior- seg7 & inferior - seg 6 Lt medial (quadrate) – Seg 4 - superior & inferior Lt lateral – Seg 3 Ventral & Seg 2Dorsal Caudate – seg 1
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Often difficult , is to determine segmental anatomy near hepatic dome – land marks are absent. Studies using arteriography: Dome was composed of - 54%: Both Rt & Lt Lobes: VIII & IVa - 41% : of only seg VIII - 5% : of only seg IVa
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Anatomic variants - Sliver (Beaver tail) of liver - Papillary process of caudate lobe (- Riedel’s lobe - ?Anomaly) - Pseudoaccessory fissures True accessory fissure Pedunculated accessory lobes Agenesis, hypoplasia , aplasia * Aplasia/hypoplasia of Lt lobe – Gastric Volvulus
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Examination techniques & appearance of normal liver Radionuclide scintigraphy Technetium Tc 99m (99mTc) sulfur colloid scan : was hallmark : phagocytized by RE cells, kupffer & tumors don’t. ** SPECT - small lesion detection but CT & MRI
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Currently, - Iodine 131 Meta- iodobenzyl Guanidine : NET - Indium 111 Leukocyte studies: Infectious - 99mTc sulfur Colloid scan: FNH - 99m Tc tagged erythrocyte scan : hemangiomas
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T2W – pheochromocytoma with liver metastasis 99mTc sulfur colloid - photopenic MIBG scan – increased tracer activity
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Evolving area - Tumor localization/specific/ scintigraphy * Immunoscintigraphy: to trace Ag expressed by certain tumors: whole body staging *Tumor receptor imaging: certain tumors have receptors for certain type of pr or hormones - Positron-emission tomography (PET) 18 FDG: metabolic activity & co-registration with CT/MRI
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Metastatic pancreatic neuroendocrine carcinoma with multiple liver lesions. A: Coronal 3D reconstruction demonstrates multiple tracer avid lesions sited predominantly in the right hypochondrium; B: Axial PET and PET/CT of the liver shows multiple somatostatin receptor rich lesions in the liver.
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Ultrasonography - expertise & body habitus - subcostal & intercostal - 2.5 to 3.5 MHz, 5MHz, ---- FZ, TGC !!!!! - complete: Evaluation of parenchymal echogenecity: relative Intrahepatic biliary tree & vasculature * Left lobe (t & L), Right lobe (Portal v conf, IVC & hepatic vv , Liver with Right K)
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Size: MCL ---13.5 to 15.5cm, two measurements (long, AP) ---volumetric --- Subjective evaluation ** Inferior angle - 45 for LL, 90 for RL ** RL with sup 2/3 of RK as a uniform, sponge-like texture of low-level gray and slightly more reflective than the adjacent renal cortex. Portal vein branches vs the hepatic veins (29%) Portal v Vs Dilated intrahepatic biliary ducts - Too many vessels (RPV), Irregular walls, stellate confluence, acoustic enhancement, peripheral location On Doppler examination, the normal hepatic vein trace reflects the transmitted right-heart pressure changes while the portal vein trace is normally continuously antegrade (with a mean peak velocity of approximately 15–25 cm/s) with slight breathing/cardiac variation. THI – Tissue Harmonic imaging Intraoperative (5 – 10MHz) - 7-46% more lesions Contrast U/S : IV ultrasound contrast agents - microbubbles stabilized by a shell -----higher lesion detection rates
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A – Atrial con X – (S) wave: systole – ventr V – Valve closure (Tri) Y – D wave : diastole – ventri: opening of tri Normally D< S D & A ---diastole S & V -----systole
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Computed tomography - mainstay for hepatocellular imaging **Conventional Vs Spiral CT Vs Dual energy CT – decrease resp misregistration – use of single breath hold & ---2 min Vs 20- 30 s - optimize enhancement. ** Technical issues - slice thickness, table incrementation, volume & administration rate of contrast, scan delay. - without & with contrast
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CT without contrast - Simplest but least informative - +55 – +65HU : glycogen, spleen 8 – 10 HU less - greatest transverse 20 to 26 cm; - vertically, near its lateral surface 15 to 21 cm; and its greatest anteroposterior diameter, determined at the level of the upper right kidney, measures 7 to 12 cm. 26 – 21 - 12 - tumors are hypodense unless well differentiated primary neoplasm - but 10 – 15% less sensitive than post-contrast ** nowadays – not done routinely (elsewhere), Ix: diffuse liver diseases (fatty liver - hemochromatosis), Cirrhosis – siderotic/dysplastic nodules calcification or hemorrhage in tumors, hypervascular metastasis ---------DECT : capability to reconstruct virtual unenhanced images similar to true noncontrast CT
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Contrast enhanced CT : Goal -to improve lesion visibility by increasing the relative attenuation difference between the lesion and normal hepatic parenchyma. - This difference (hepatic attenuation): -- phase of contrast delivery during scanning. Phases: Vascular, redistribution & Equilibrium - Timing of the phases and peak enhancement --technical factors: Scanner, concentration, vol & rate of inj --patient factors: weight & CO ** Use of Chaser bolus of 20ml of saline ** Automated bolus tracking
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Dynamic bolus Vs Dual phase Dynamic bolus iodine CT Or Single Phase Scan - Standard incremental /Spiral : - Inject 100 to 150ml of 300 –370 mgI/ml @ R=3ml/s or more - Goal: optimize contrast difference b/n normal parenchyma & liver lesions, prim hypovascular – on portal venous dominant phase. - preferred in routine hepatic evaluation - B/N portal vein enhancement & equilibrium: 60-75 sec – b/n initiation of contrast & start of scanning but before 2-3 min.
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Dual phase (Biphasic): fast scanners - helical - possible to scan liver 2x before equilibrium: arterial dominant phase & portal venous dominant phase - optimal for evaluation of hypervascular lesions (may be iso on PVDP) , these get entire bld from hep a; FNH, adenoma, HCC, met from melanoma, breast, RCC, thyroid & NET *** NC & PVDP Vs Biphasic Vs PVDP – lesion detection even hypervascular
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Protocol: requires fast injection rate (4-6ml/s) 150-175ml of 60% iodinated IV contrast * ADP at 5mm coll, 7mm spacing start 20-30 s after initiation. maximizes lesion detection * PVDP at -----, start 55-65s after initiation. for evaluation of vascular str & optimal imaging of extrahepatic organs.
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Protocols - Non-contrast enhanced - single phase (PVDP) - dual phase (ADP & PVDP) - triple phase (NC, A & PVDP) - cholangiocarcinoma (+ Delayed (15min))
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Delayed iodine CT - 4 to 6 hrs after intravascular administration of at least 60gm Iodine. - small percentage (10-12%) of I excreted by normal hepatocytes. Current use : after CT arterial portography – estimation of surgical margin & characterize non-tumor perfusion abnormality.
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Image
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Catheter assisted hepatic CT (CT angiography) - basis similar to dual phase CT CT images of liver obtained while contrast material is passed to liver by means of an indwelling catheter placed in - hepatic artery: CT during hepatic arteriography & CTAP - splenic or SMA : CT during arterial portography
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Images
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Angiography - catheter placed in selective or subselective location Current use – before chemoembolic therapy - after transplantation to r/o stenosis/thrombosis
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Dual energy CT (Spectral CT)--------- at two KV values
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MRI - Challenges : Size, motion - 0.5 to 3.0T - Attention : devoted to motion artefact reduction techniques * traditional : signal averaging * Respiratory Compensation: coupled with phase encoding steps * Rapid breath hold sequences – Spoiled GRE - T1W best with high magnetic field strengths * Use of phased array body coils * Respiratory trigger ** pulsatility artefact –Aorta or IVC - spatial presaturation/ flow compensation ** Artefacts related to bowel movemnts – fast sequences or antiperistalitic agents
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In general, - both T1W & T2W sequences are necessary for complete exam. - T1 giving anatomic detail & better in low to mid magnetic field strengths & T2 with better lesion detection, - Non-contrast: Higher T1 signal intensity than muscle & kidneys & a lower T2 signal intensity than spleen, kidneys & pancreas - higher intracellular bound water: pancreas, adrenals, muscle Vs kidneys, spleen,& penis , Ovaries & thyroid, prostate, seminal vessicles & testis - higher protein & RER : Intermediate on T1 - Biliary tree, - Hepatic veins & portal veins - beware hyperintense inflow artefacts precontrast
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For T1W imaging , numerous sequences are available: - conventional SE TR<300 & TE < 15msec - GRE with TR of 50 – 150ms, TE <6ms & 80 – 90’ flip angle (Eg: Spoiled GRE, Volume interpolated breath hold exam (VIBE) – dynamic imaging) - IR magnetization – 180’ prepulse followed by all portions of the phase encoding steps
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For T2W imaging, sequences available include - Conventional SE TR >2000ms & TE>80ms - Echoplanar imaging: T/FSE ------with fat saturation - HASTE/SSFSE STIR --------- T2/T1
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Postcontrast studies - help in lesion characterization Vs CT detection A. Non-specific Gadolinium chelates: - Extracellular Agents: – most commonly used agent - shortens relaxation times – equil 2 min – T1w GRE sequences with FS - dynamic imaging, 30 s- 70 s- 5 min Eg: Gadopentetate dimeglumine (Gd-DTPA), gadoteridol (Gd-HP-DO3A), gadodiamide (Gd-DTPA-BMA), gadoversetamide (Gd-DTPA-BMEA), gadoterate meglumine (Gd-DOTA), and gadobutrol/Gadovist(Gd-BT-DO3A)
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B. Hepatocyte targeted Agents : active transport into hepatocytes and metabolized ---- biliary excretion ** Gd Based - Gd-BOPTA (Gadobenate dimeglumine), - Gd- EOB- DTPA (Gadoxetate/Eovist): hepatocyte sp PM agents –adds hepatobiliary phase (20min) to dynamic ** Mn Based : administered over 2 min. - Manganese dipyridoxyl diphosphae /MnDPDP/: hepatocytes (T1W) C. RES-specific contrast agents : at least 30 min, RE cells, Usu T2W – Superparamagnetic iron oxide /SPIO/ or USPIO
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- Extracellular contrast A
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SPIO ----T1—60min HCC FNH HCC Met Ade Pre SPIO Gd (Art, Ve)
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After Mn Before
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Patient with colorectal metastasis after RFA of s 6 lesion---Eovist
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Other sequences - T1W sequences using opposed phase imaging : GRE sequences obtained when signals from water &TG are in phase & opposite (out of phase) ====signal loss signifying microscopic fat: fatty liver, some adenomas & HCC’s MRA – advantage : noninvasive, multiplanar
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Fat only , water only
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Protocol : MRI of liver ---< 20min - GRE (BH)– T1W : in – out of phase, water only, fat only - STIR & MRCP (RT) – T2W - GRE (BH) – FS – PC T1W : three arterial, portal & equil