Section for Residents

L S: U E

Diego Sebastián de Jesús Castro

Abstract Resumen

The is the largest solid organ in the normal that oc - El hígado es el órgano sólido de mayor tamaño en el abdomen nor - cupies the right . It weighs 1500 grams approxima - mal, ocupando el hipocondrio derecho. Pesa 1500 grs aproximada - tely and has a reddish brown coloring. The of surface mente y tiene una coloración parda rojiza. En la anatomía de recognizes 4 lobes. The first anatomist to study liver division was superficie se reconocen 4 lóbulos. El primer anatomista que estudió James Cantlie. In 1957, Goldsmith and Woodburne proposed a liver la funcionalidad hepática fue James Cantlie. En 1957, Goldsmith y segmentation system based on the suprahepatic veins. In 1957, Coi - Woodburne proponen un sistema de segmentación hepática basado naud proposed another segmentation following the portal branches en las venas suprahepáticas. En 1957, Coinaud propone otra si - from the superior view, in clockwise and in spiral sequence matching guiendo las ramificaciones portales, en el sentido de las agujas del the districts or "arrondissements" of Paris. That is to say the supra - reloj con números romanos, en secuencia espiral coincidentes con hepatic veins act as limits of independent biliary drainage and irri - los barrios o “arrondissements” de París. Es decir que las venas su - gation areas. For liver segmentation will make axial and prahepáticas actúan como límites de áreas de irrigación y drenaje longitudinal views using 3.5-5 Mhz convex probes in epigastrium, biliar independientes. Para la segmentación hepática realizaremos with angles toward right and left shoulder, allowing the visualization cortes axiales y longitudinales utilizando sondas convex de 3.5-5 segments I, II, III, IVa and b, V and VIII respectively, while with sa - MHz., en epigastrio, con angulaciones hacia hombro derecho e iz - gittal view in axillary line display segments VI, VII and VIII. Finally quierdo, permitiendo visualizar segmentos I, II, III, IV a y b, V y VIII parasagittal views will make possible to complement the visualiza - respectivamente, en tanto que con cortes sagitales en línea axilar tion of segments I, II, III, V and VIII. Understanding the anatomy visualizaremos segmentos VI, VII y VIII; finalmente los cortes para - and making correct interpretations would bring a number of unde - sagitales permitirán complementar la visualización de segmentos niable advantages for the surgeon. The segmental liver resection is I, II, III, V y VIII. Es así que el conocimiento de la anatomía y la the treatment of current choice for various diseases and tumor pro - correcta interpretación aportan una serie de ventajas innegables cesses. While Ultrasound presents the disadvantage of being opera - para el cirujano. La resección segmentaria del hígado constituye el tor-dependent, it is a method that is simple and easy to use and, at tratamiento de elección actual de las diversas afecciones y procesos the same time, it allows a significant correlation with the anatomy. tumorales. Si bien la ecografía presenta la desventaja de ser opera - dor-dependiente, es un método sencillo y fácil de utilizar, al mismo tiempo que permite una correlación notable con la anatomía. key words: Liver segmentation – Ultrasound evaluation. Palabras claves: Segmentación hepática- Evaluación ecográfica.

Contact: Diego Sebastián de Jesús Castro Hospital Centro de Salud Zenón Santillán. Recibido:  de abril  / Aceptado:  de mayo  San Miguel de Tucumán - Tucumán, Argentina. Recieved: April ,  / Accepted: May ,  e-mail: [email protected]

Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, .  Liver Segmentation: Ultrasound Evaluation. Castro, D.

Introduction and the vena cava at the back (Fig. 2). Physicians who studied the intrahepatic division could deter - The liver is the largest solid organ in the normal ab - mine the segmentation based on the vascular and domen and it occupies the right hypochondrium al - biliary anatomy. (1, 3, 4) most entirely (Fig. 1). It weighs approximately 1,500 The first anatomist who understood that the truth grams and has a reddish brown color. It stays in its functional division of the liver did not correspond position thanks to the inferior vena cava, to which to the superficial anatomy was Sir James Cantlie, it is connected by the suprahepatic veins, to the from Scotland. Taking into account the distribution liver round ligament which replaces the umbilical of the vascular tracts, in 1987 he proposed a sepa - vein in adults, and to peritoneal attachments such ration through the plane delimited by the vesicular as coronary and triangular ligaments. bed and the inferior vena cava (called from then on From the purely anatomical point of view, it is di - Cantlie line) (Fig. 3). vided into 4 lobes: Right lobe, located at the right The current concept of an organ segment is: "The of the falciform ligament; left lobe, extended over smallest portion of an organ which contains the the and located to the left of the falciform same elements of the hilum and which performs ligament; quadrate lobe, only visible in the interior the same functions of that organ." face of the liver and limited by the venous ligament to the left (Arantius canal or venous ductus), by the vesicular bed to the right and by the hepatic portal; caudate lobe or Spiegel's lobe, located between the posterior margin of the hepatic portal at the front

Fig. : The liver is the largest solid organ in Fig. : Scheme of the liver the normal abdomen; it occupies the shows from the middle of the liver up, right hypochondrium almost entirely. the division of the liver into right and left lobes, over the anterior and supe - rior face, by the falciform ligament. From the middle of the liver down, the inferior face with quadrate and cau - date lobes.

 Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, . Liver Segmentation: Ultrasound Evaluation. Castro, D.

Fig. : Sir James Cantlie. First anatomist, from Scotland, who understood the functional liver division and who, in , proposed the distribution of vascular beds by a separation through the plane delimited by the vesicular site and the inferior vena cava (which came to be known as Cantlie line).

Liver Segmentation lobe and divides it in a lateral and a paramedian "sector"; whereas the left lobe has the plane of the In 1957, Goldsmith and Woodburne proposed a left suprahepatic vein as a limit of the medial and segmentation system for the hepatic anatomy based lateral sectors, since they are considered terminal on the distribution of the hepatic veins: segmentary branches from the portal vein to the Middle hepatic vein which separates the right umbilical portion of the left branch (for the seg - lobe from the left lobe; right hepatic vein which di - ments IVa and IVb) and to the segment II. vides the right lobe into two segments, anterior and In Brisbane in 2000, the terminology committee posterior; left hepatic vein which divides the left of IHPBA (International lobe into two segments, medial and lateral; caudate Hepato-Pancreato-Biliary Association) agree on a lobe which is a separate segment, limited by the global division and terminology, based on the func - IVC at the back, having the venous ligament fissure tional and surgical anatomy of three orders: as an anterior margin. • First-order division: cut plane which goes According to Coinaud, the intrahepatic branches through the middle suprahepatic vein, dividing the of the portal vein do not coincide with the planes hemi-liver into right and left. of the suprahepatic veins tract. As a result of this • Second-order division (intersectional planes): premise, both venous systems are interdigitated. based on the alternation between the glissonian pe - That is to say that the suprahepatic veins act as li - dicles and hepatic veins, the right hemi-liver is di - mits of irrigation areas and independent biliary drai - vided into a posterior and an anterior segment, nage. Based on the intrahepatic distribution of the following the right suprahepatic vein (intersectional glissonian pedicles, in 1957 Coinaud presented a plane). On the other hand, the left hemi-liver is di - hepatic systematization in segments, numbering vided into medial and lateral segment, following the them clockwise for the frontal upper face and coun - round and falciform ligament plane. terclockwise for the lower face, with roman num - • Third-order division: these are the intersegmen - bers, inspired by the same spiral sequence of the tal planes, dependent upon the glissonian pedicles. neighborhoods or "arrondissements" of Paris. The In this case, segments are numbered with Arabic systematization is also based on the intraparenchy - numbers, instead of Roman. matous distribution of the hepatic hilum branches (Each of these sections is divided transversally by and on the hepatic areas dependent upon the hilum an imaginary plane which goes through the origins (Fig. 4). of the right and left Portal Vein). (1, 2) Coinaud keeps the American division of the right

Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, .  Liver Segmentation: Ultrasound Evaluation. Castro, D.

At present, surgeons can excise hepatic subseg - Dorsal intermediate caudate segment ments. The system by Coinaud divides the left late - 7. Upper posterior lateral zone - Segment VII - ral, anterior right and posterior right segments into Dorsal intermediate cranial segment upper and lower subsegments, and keeps the cau - 8. Upper frontal lateral zone - Segment VIII - Ven - date lobe and left middle segment as unique seg - trocranial segment ments. This data was obtained from the IHPBA Termino - Hence, we recognize the following anatomic seg - logy Committee in the IHPBA 2000 World Congress ments (classification by Healey-Coinaud-Hjorstjo- in Brisbane, Australia (5-7). Woodburne): For this article, it is necessary to remember the 1. Caudate lobe - Segment I - Dorsal segment anatomic characteristics of the liver and know the 2. Lateral upper zone - Segment II - Dorso-lateral imaging characteristics of the ultrasound evaluation, left segment in order to be able to correlate the theory with the 3. Lateral lower zone - Segment III - Ventrolateral hepatic pathology in the future. left segment 4. Left medial upper and lower zone - Segment IVa and IVb - Ventral and dorsal central segment 5. Right medial frontal lower zone - Segment V - Ventrocaudate segment 6. Lower posterior lateral zone - Segment VI -

Fig. : Claude Coinaud. In  he proposed liver segmentation following portal ramifications in a clockwise direction with roman numbers, taking as a model the spiral distribution of "arrondissements" or neighborhoods in Paris in relation to the Sena river.

Ultrasound Evaluation which is only interrupted by portal spaces and he - patic veins. Its echogenicity is slightly superior than Ultrasound is a two-dimension exploration and thus or equal to the right kidney, but inferior than the the operator must recognize the third dimension of spleen. At the same time, its echogenicity is less space by moving the transducer. It allows for the than the ; that is to say hypoecogenic. The identification of not only the number and exact lo - size of the liver is often hard to measure since the cation of intrahepatic lesions but also of their rela - distribution of the right and left lobe volume varies. tion to vascular structures. The upper limit of normality as regards the length Prior to that, it is necessary to recognize some of the liver goes from 13 to 17 cm, measured from useful anatomic comments for the interpretation of the mid-clavicular line. the images. The liver presents a homogeneous architecture

 Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, . Liver Segmentation: Ultrasound Evaluation. Castro, D.

The suprahepatic veins are visualized as tubular ane - • Segments II, III, IVa and IVb (lateral and medial choic structures which drain in the inferior vena segments of the left lobe, respectively): oblique tran - cava, giving an image similar to the antlers of a section view with cephalic inclination to the left, at moose. Three can be recognized: right, middle and the level of the subcostal angle where the portal vein left. On the other hand, portal veins are differentiated left branch is divided in the shape of a "ballet dan - from hepatic veins by the fibroadipose periportal tis - cer", in such a way that the ends of the segments co - sue which produces strong echoes around portal rrespond to the segment III (lateral inferior) and veins, hepatic arteries and adjacent biliary canaliculi. segment II (lateral superior). Meanwhile, the trunk of In order to differentiate them from the latter two, it the ballet dancer allows for the visualization of medial is necessary to use a color Doppler test. While he - segments, superior and inferior; that is to say, seg - patic veins separate liver segments, portal veins go ment IVa and IVb (Fig. 7). In the same way, looking through those segments and each branch is called for the portal H (hilum) with an axial plane in the after the segment it drains. The round ligament also epigastrium, left segments will be visualized. (Fig. 8). constitutes a useful reference since it is located bet - • Superior segments (II, IVa, VII and VIII): oblique ween the medial and lateral segment of the left liver transection scanning plane with a cranial inclination lobe. It has the fibrous remains of the umbilical vein and an angle towards the right shoulder which will and it flows between the navel and the anterior face show suprahepatic veins ("claw-like image"). Based of the umbilical segment of the left portal vein. on the angle, segment IVa can be visualized between Another ultrasound element to be recognized is the middle and left hepatic veins, lateral to it; seg - the interlobular fissure, which is a slightly deep in - ment VIII moving up and segment V moving down. dentation of the posterior face of the liver which se - Segment VII can be visualized from the outside of parates the right liver lobe from the left liver lobe the right hepatic vein. and identifies the situation of the vesicular cavity. • Medial and inferior segments (IVb and V): obli - Finally, it is necessary to visualize the caudate or que transection scanning plane directed to the right Spiegel's lobe, which is a small segment of the liver shoulder, swing slightly elevating the transducer to - located immediately before the IVC. It is next to the wards the inferior region of the liver. Segment IV can right lobe and it is separated from the later segment be visualized from within the middle hepatic vein of the left lobe by the venous ligament fissure. and segment V from outside of it (Fig. 9). The anatomy of the liver has always been the • Right segments: in order to visualize right seg - same, but its interpretation has evolved according to ments some axial views mentioned earlier have to the development of the imaging diagnosis methods be combined, especially for the visualization of seg - and the improvements in resection surgery (hepa - ment V, which is anterior and inferior, with longitu - tectomy). (1, 3, 5.7) dinal scanning planes over the axillary line. For the Fig. 5 shows the scanning planes necessary to vi - last segments (VI, VII, VIII) sagittal views are used, sualize the segments. between the axillary middle and posterior line in the In this way, the segments that can be visualized last intercostal spaces. A visualization of right kidney will be as shown in the figure, taking into account and Morrison's pouch for segments VI and VII. The that they can be identified following the portal bran - segment underlying the middle section of the kidney ches as well as the suprahepatic branches: is segment VI (posterior and inferior). The segment • Segment I: oblique subxiphoid transection view, next to the upper pole of the kidney is segment VII with cranial inclination and an angle towards the left (posterior and superior). The segment VIII is also shoulder. Swing slightly elevating the transducer to - identified with an axial view and an angle in the epi - wards the middle area of the liver. Another view gastrium towards the right shoulder. The right branch used is the right paramedian sagittal cut in epigas - of the portal vein can be visualized; the segment un - trium. In the first and second scanning planes, seg - derneath the vein is segment VII and the one over ment I to left segments are visualized "below" the the vein is seg ment VIII (Fig. 10). (1, 6, 8). venous ligament fissure and medial in relation to the IVC. (Fig. 6).

Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, .  Liver Segmentation: Ultrasound Evaluation. Castro, D.

Understanding the anatomy and making correct in - With the development of liver surgery and the high terpretations would bring an important number of frequency of biliary pathologies and the appearance advantages for surgeons. The segmental liver resec - of diagnostic imaging methods, there is a need for tion is the treatment of current choice for various di - the accurate location of the lesions and thus the to - seases and tumor processes, either benign, malignant pographical knowledge is necessary. or traumatic lesions. As regards imaging methods, it can be concluded that ultrasound is a sensitive me - thod not only for the parenchyma evaluation but also for the intra and extrahepatic . Des - pite the disadvantage of being operator-dependent, it is still simple and easy to use and at the same time, it allows for a significant correlation between the images, the truth hepatic and biliary anatomy.

Fig. : Scheme showing the most frequent positions (sagittal, parasagittal and axial with angles in epigastrium) of the transducers to evaluate the different liver segments.

Fig. : Left: Axial cut in epigastrium with a slight angle towards the left shoulder, in which the caudate lobe or seg - ment I is identified. Note the relations with the venous ligament, portal ramifications and its close contact with the inferior vena cava. Right: Paramedian sagittal cut also in epigastrium, in which caudate segment I is identified in the left lobe.

 Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, . Liver Segmentation: Ultrasound Evaluation. Castro, D.

Fig. : Visualization of medial left segments (IVa and IVb) and lateral segments (II and III). Axial cut in epigastrium with an angle towards the left side, shows the inferior hepatic face, in which the "image of the ballet dancer" needs to be identified. The trunk (marked with yellow lines) corresponds to the left ramification of the portal vein and represents the segments IVa and IVb; the "legs" correspond to the branches for the segments II and III.

Fig. : Axial subxiphoid cut in epigastrium without angles in which the hepatic H is visualized. It corresponds to the medial and lateral ramification with which we can recognize all left segments.

Fig. : Left: Axial cut in epigastrium with an angle towards the right shoulder in which the right segments are visuali - zed, anterior (such as inferior V and superior VIII) and left (II, III, IV). Right: Axial cut with a maximum angle towards the right, in which the segment branches of the right portal vein are visualized and segments V and VIII can be identified.

Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, .  Liver Segmentation: Ultrasound Evaluation. Castro, D.

Fig. : Sagittal cut in right axillary medial line, in which Morrison's pouch, the hepatic parenchyma and the right kidney are vi - sualized. The most posterior segment is VII, the middle is VI, and the anterior is V.

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 Rev. Arg. Diag. por Imágenes Vol.  / Nº - Agosto, .