Hepatomegaly

Japanese: 肝腫大

Concept Hepatomegaly is a condition in which the liver is partially or entirely enlarged. It is usually diagnosed by palpating the right subcostal or epigastric area during abdominal palpation, but it can also be diagnosed by plain abdominal X-ray, abdominal ultrasound, CT, or MRI. A normal liver is soft and difficult to palpate. However, in healthy people with an elongated body type or emphysema, the liver is located lower and can be palpated under the right costal arch. Therefore, even if the liver can be palpated, it does not mean that the liver is enlarged. The lower edge of the left lobe of the liver is located several centimeters below the xiphoid process, but it is flat, thin, and soft and cannot be palpated. Furthermore, the rectus abdominis muscle and abdominal wall fat in front of it make it even more difficult to palpate. In enlarged, pathological livers, the liver is often hard and can be easily palpated. The size of the liver is estimated from the distance between the lung-liver border and the lower edge of the liver (hepatic dullness area). The lung-liver border on the midclavicular line is located at the fifth intercostal space in people with a normal body type. The pulmonary-liver border fluctuates by 1 to 3 cm with deep breathing. The normal hepatic dullness boundary is about 11 cm, and if it exceeds this value significantly, liver enlargement is suspected.
In addition to various liver diseases, hepatomegaly can also be seen in congestive liver due to congestive heart failure, metabolic diseases such as amyloidosis, and blood diseases such as leukemia and malignant lymphoma (Table 2-15-1).
Pathophysiology: The liver is the largest organ in the body, and in adults the liver weight is approximately 1/50 of body weight, 1300-1500 g in men and 1100-1300 g in women. Mechanisms that cause hepatomegaly include inflammation (degeneration and necrosis of hepatocytes, swelling, inflammatory cell infiltration), fibrosis, deposition of various substances, tumors, blood flow disorders, and cholestasis.
In acute hepatitis and drug-induced liver injury, hepatomegaly occurs due to inflammatory cell infiltration and cellular swelling. The liver has a smooth surface, is soft in consistency, and has a sharp margin that can be palpated and is often tender. In chronic hepatitis and cirrhosis, hepatomegaly occurs due to fibrous deposition, cellular swelling (balloon-like swelling), and inflammatory cell infiltration, and liver stiffness increases due to fibrous deposition. In cirrhosis, the liver has a blunt margin, nodular surface, is elastically hard to firm, and is not tender.
In leukemia and malignant lymphoma, hepatomegaly occurs due to infiltration of leukemic cells into the liver.
In fatty liver, neutral fat accumulates within hepatocytes, causing hepatomegaly. A smooth liver with blunt margins is palpable and there is no tenderness. In alcoholic liver disease, hepatomegaly is caused by fatty liver, cellular swelling, inflammatory cell infiltration, and fibrosis. In alcoholic cirrhosis, significant hepatomegaly can be seen, reaching the navel, due to fatty deposition. In primary hepatocellular carcinoma and metastatic liver cancer, hepatomegaly is caused by intrahepatic tumors. The liver is irregularly uneven and palpable as a hard liver. In liver abscess, hepatomegaly is caused by an abscess within the liver. In giant liver cysts and multiple liver cysts, the liver is swollen due to the cysts and is palpable as a hard liver with a smooth surface and no tenderness.
In patients with heart failure or Budd-Chiari syndrome, the liver becomes enlarged due to blood congestion. The smooth, elastically hard liver can be palpated and is often tender to the touch. In patients with amyloidosis, in which amyloid is deposited in the liver, there is marked hepatomegaly and the liver becomes extremely hard. In patients with congenital metabolic disorders of glycogen, phospholipids, and mucopolysaccharides, these substances accumulate in the liver, causing hepatomegaly.
In extrahepatic obstructive jaundice, the intrahepatic bile duct becomes dilated, causing hepatomegaly.
Diagnosis <br /> Hepatomegaly is diagnosed by physical examination and imaging.
1) Physical examination:
When palpating the liver, the subject should be in a supine position with both legs flexed to relax the abdominal wall. Place the fingers of the right hand parallel to the costal arch against the abdominal wall, and while gently pressing the fingers under the costal arch, have the subject breathe abdominally while palpating the lower edge of the liver. Record how many centimeters from the costal arch the lower edge of the liver is located, and how many centimeters the hepatic dullness area is. Also record the presence or absence of tenderness, the presence or absence of unevenness, hardness (soft, elastic hard, hard), shape of the edge (sharp or blunt), and the presence or absence of a vascular murmur.
Auscultation is also useful in differentiating between the hepatomegaly and the liver. A rub is often due to a recent liver biopsy, tumor, or perihepatitis. A venous bruit may be heard between the xiphoid process and umbilicus in portal hypertension. A hepatic arterial bruit is often due to hepatocellular carcinoma.
2) Diagnostic imaging:
On plain abdominal X-rays, the liver appears as a wedge-shaped, homogenous soft tissue shadow under the right diaphragm. Liver size is measured as the vertical difference between the highest point of the right diaphragm and the lower pole of the right liver lobe; if it is 22 cm or more, hepatomegaly is suspected. Abdominal ultrasound is useful for diagnosing hepatomegaly. Right lobe enlargement is diagnosed if the vertical diameter is 15.5 cm or more on a right hepatic lobe longitudinal scan, and the anteroposterior diameter is 13 cm or more on a right hypochondriac scan. Left lobe enlargement is diagnosed if the anteroposterior diameter is 8 cm or more on a left hepatic lobe longitudinal scan. Liver volume can be calculated from CT data. Standard liver volume (mL) can be calculated as 706.2 × body surface area ( ^m2 ) + 2.4.
Differential diagnosis When considering the cause of hepatomegaly, the characteristics of the enlarged liver and other physical findings and symptoms are useful references.
In particular, enlarged livers are seen in patients with liver tumors, multiple liver cysts, alcoholic cirrhosis, congestive liver, malignant lymphoma, and amyloidosis. When hepatomegaly is accompanied by splenomegaly (hepatosplenomegaly), liver disease or blood disease is suspected.
If the liver is enlarged and accompanied by tenderness, acute hepatitis, liver abscess, liver cancer, or liver congestion may be suspected.
Remittent fever is seen in liver abscess. The presence of ascites and abdominal venous distention raises suspicion of liver cirrhosis or Budd-Chiari syndrome.
If an enlarged liver suddenly shrinks, this may be due to acute hepatitis becoming severe or alcoholic hepatitis becoming more severe. Conversely, in the case of tumorous lesions, the degree of hepatomegaly will rapidly worsen. [Kentaro Yoshioka]

Table 2-15-1
Causes of Palpable Liver or Hepatomegaly ">

Table 2-15-1

Source : Internal Medicine, 10th Edition About Internal Medicine, 10th Edition Information

Japanese:

概念
　肝腫大とは肝臓が部分的，あるいは全体的に腫大している状態をいう．通常は腹部触診の際に，右肋弓下または心窩部に腫大した肝を触れることにより診断するが，腹部単純X線，腹部超音波検査，CT，MRIなどで診断されることもある．　正常肝はやわらかいため触れにくい．しかし健常人でも細長型体型の人や肺気腫のある人では肝臓が下方に位置しており，右肋弓下に触れることがある．したがって肝が触知しても，肝腫大とはいえない．肝左葉下縁は剣状突起下数cmに位置しているが，扁平で薄く，軟らかいため触知されない．また前方にある腹直筋や腹壁脂肪のため，さらに触知困難となっている．腫大した病的肝では硬度が増していることが多く，容易に触れることができることが多い．肝臓の大きさは肺肝境界（lung-liver border）と肝下縁の距離（肝濁音界）から推測する．鎖骨中線上の肺肝境界は普通の体型の人では第5肋間に位置する．肺肝境界は深呼吸により1〜3 cm程度変動する．肝濁音界は正常では11 cm程度であり，この値を大きくこえれば肝腫大があると思われる．
　肝腫大は各種肝疾患以外に，うっ血性心不全によるうっ血肝やアミロイドーシスのような代謝性疾患，白血病や悪性リンパ腫のような血液疾患でもみられる（表2-15-1）．
病態生理
　肝臓は体内で最も大きな臓器であり，成人の肝重量は体重の約1/50であり，男性1300〜1500 g，女性1100〜1300 gである．肝腫大をきたす機序は，炎症（肝細胞の変性や壊死，腫大，炎症性細胞浸潤），線維化，種々の物質の沈着，腫瘍，血流障害，胆汁うっ滞などである．
　急性肝炎や薬剤性肝障害では炎症性細胞浸潤や細胞の膨化により肝腫大が起こる．表面は平滑，硬さは軟，辺縁鋭の肝が触知され，しばしば圧痛がある．慢性肝炎や肝硬変では線維の沈着と細胞の膨化（風船様腫大），炎症性細胞浸潤により肝腫大をきたし，線維の沈着により肝硬度が増している．肝硬変では肝は辺縁鈍で，表面に結節があり，弾性硬〜硬で，圧痛はない．　
　白血病や悪性リンパ腫では白血病細胞の肝内浸潤により肝腫大をきたす．
　脂肪肝では肝細胞内に中性脂肪が蓄積し，肝腫大をきたす．辺縁鈍で表面平滑な肝が触知され，圧痛はない．アルコール性肝障害では脂肪肝，細胞の膨化，炎症性細胞浸潤，線維の蓄積が肝腫大の原因となっている．アルコール性肝硬変では，脂肪沈着などにより臍にまで及ぶ著しい肝腫大を認めることがある．　原発性肝細胞癌や転移性肝癌では，肝内の腫瘍により肝腫大が起こる．不整な凹凸があり，硬い肝として触知される．肝膿瘍では，肝内の膿瘍により肝腫大が起こる．巨大肝囊胞や多発性肝囊胞では囊胞により肝が腫大し，硬い肝として触知され，表面は平滑であり，圧痛はない．
　心不全やBudd-Chiari症候群ではうっ血により肝が腫大する．表面平滑で弾性硬の肝が触知され，しばしば圧痛を伴う．　アミロイドが肝に沈着するアミロイドーシスでは著明な肝腫大がみられ，肝はきわめて硬くなる．グリコーゲン，リン脂質，ムコ多糖の先天性代謝異常では，これらの物質が肝に蓄積し肝腫大をきたす．
　肝外閉塞性黄疸では肝内胆管が拡張し肝腫大をきたす．
診断
肝腫大は身体診察と画像診断により診断される．
１）身体診察：
肝を触診する際は，仰臥位にて，腹壁を弛緩させるため両下肢を屈曲させる．右手指を肋骨弓に平行に腹壁に当て，肋骨弓下に指を差し込むように軽く押し当てながら，被検者に腹式呼吸をさせ，肝下縁を触知する．肝下縁が肋骨弓から何 cmに触れるか，また肝濁音界は何cmか，記録する．圧痛の有無，凹凸の有無，硬さ（軟，弾性硬，硬），辺縁の形状（鋭または鈍），血管雑音の有無についても記録する．　
肝腫大の鑑別においては，聴診も有用である．摩擦音は最近施行された肝生検や腫瘍，肝周囲炎によることが多い．門脈圧亢進症では静脈雑音が剣状突起と臍の間で聴かれる．肝の動脈雑音は肝癌によることが多い．
２）画像診断：
腹部単純X線では，肝臓は右横隔膜下に楔形の均質な軟部組織陰影を呈する．肝の大きさは右横隔膜の最高点と肝右葉下極の上下差で計測し，22 cm以上あれば肝腫大が疑われる．　腹部超音波検査は肝腫大の診断に有用である．肝右葉縦走査で上下径が15.5 cm以上，右季肋下走査で前後径が13 cm以上であれば右葉腫大と診断する．肝左葉縦走査で前後径が8 cm以上では左葉腫大と診断する．　CTデータより肝容積を計算できる．また標準肝容積（mL）は706.2×体表面積（m²）＋2.4で計算できる．
鑑別診断
　肝腫大の原因を考えるうえで，腫大肝の性状やその他の身体所見，症状が参考になる．
　特に巨大な肝は，肝腫瘍，多発性肝囊胞，アルコール性肝硬変，うっ血肝，悪性リンパ腫，アミロイドーシスでみられる．　肝腫大とともに脾腫が存在するときは（hepatosplenomegaly），肝疾患や血液疾患が疑われる．
　肝腫大に圧痛を伴う場合は，急性肝炎，肝膿瘍，肝癌，うっ血肝などが考えられる．
　弛張熱は肝膿瘍でみられる．腹水や腹壁静脈怒張がある場合は肝硬変やBudd-Chiari症候群が疑われる．
　腫大していた肝が急に小さくなる場合，急性肝炎の劇症化やアルコール性肝炎の重症化が考えられる．逆に腫瘍性病変では，肝腫大の程度が急速に悪化する．［吉岡健太郎］

表2-15-1
肝触知あるいは肝腫大の原因">

表2-15-1

出典　内科学第10版内科学第10版について　情報

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