Sonographic features of amebic and pyogenic liver abscesses: a blinded comparison

We blindly compared the sonographic findings in amebic (112 lesions) and pyogenic (30 lesions) liver abscesses. Two sonographic features were significantly more prevalent in amebic abscesses: the lesions had a round or oval shape and the lesions had an echogenicity that was lower than that of normal liver and were internally homogeneous on high-gain scans. Amebic abscesses were round or oval in 92 instances (82%), while 18 pyogenic abscesses (60%) (p less than .01) had these shapes. Fifty-nine (58%) of 101 amebic abscesses displayed low echogenicity and homogeneous internal echoes with high-gain settings compared with nine (36%) of 25 pyogenic abscesses (p less than .04). Despite these different sonographic patterns, image findings alone were inadequate in distinguishing pyogenic from amebic liver abscesses. However, when the sonographic findings were coupled with clinical and laboratory data, a correct diagnosis was possible in 83 (86%) of 96 patients with amebic abscess. It appears that, although some sonographic features of amebic abscess differ from those of pyogenic abscess, these differences are not sufficient to allow a specific diagnosis on the basis of sonography alone. Sonography can expedite abscess detection and, when coupled with clinical and laboratory data, can aid in differentiating pyogenic from amebic liver abscesses.     

Pyogenic hepatic abscesses: MRI findings on T1- and T2-weighted and serial gadolinium-enhanced gradient-echo images

The purpose of this study was to determine the magnetic resonance imaging (MRI) features of pyogenic hepatic abscesses on T1-weighted, T2-weighted, and serial gadolinium (Gd)-enhanced T1-weighted spoiled gradient-echo (SGE) images including images acquired in the immediate, intermediate, and late phases of enhancement. The MRI studies of 20 patients with pyogenic liver abscesses were retrospectively reviewed. All patients were examined on 1.5 (n = 19) and 1.0 (n = 1) T MR scanners. MR studies included T1-weighted, T2-weighted, and serial Gd-enhanced SGE images. The following determinations were made: signal intensity of the abscess cavity and perilesional liver tissue, and the presence of internal septations, layering material, or air in the abscess cavity. The pattern of enhancement of the abscess wall, internal septae and peri-abscess liver were evaluated on serial Gd-enhanced SGE images. A total of 53 abscesses were observed in the 20 patients. Fortyeight abscesses were hypointense on T1-weighted and hyperintense on T2-weighted images. Internal septations were present in four abscesses. Lower signal intensity material was observed in a dependent location on T2-weighted images in one abscess. Signal void foci of air located on the nondependent surface was observed in two abscesses. Two other abscesses contained signal void air that occupied the entire abscess cavity, observed on all imaging sequences. On serial gadolinium-enhanced images, all abscesses revealed early enhancement of the wall, which persisted with negligible change in degree of enhancement or thickness on delayed images. Abscess walls ranged in thickness from 2 to 5 mm. Internal septations ranged in thickness from 2 to 3 mm. Abscess walls and septations were relatively uniform in thickness with no evidence of focal nodularity. Periabscess liver tissue was mildly hypointense on T1-weighted and mildly hyperintense on T2-weighted images in 20 lesions, which were either circumferential (n = 12) or wedge-shaped (n = 8). All these regions enhanced more than the remainder of the liver on immediate post-gadolinium images and remained relatively hyperintense on late phase images. Periabscess liver parenchyma was isointense on both T1- and T2-weighted images in 18 lesions, and in these lesions wedge-shaped subsegmental (n = 6) or segmental (n = 12) enhancement was observed on immediate gadolinium-enhanced images, which faded to isointensity on intermediate phase images. No perilesional signal changes and enhancement difference was observed in 15 lesions. Characteristic features of abscesses include: intense mural enhancement on early gadolinium-enhanced images, which persists with negligible change in thickness and intensity on later post-gadolinium images, and the presence of periabscess increased enhancement on immediate post-gadolinium images. These MRI features may help to distinguish abscesses from other focal liver lesions during differential diagnosis.     

肝脓肿的MRI平扫及动态增强信号特征分析

目的：探讨肝脓肿的MRI平扫及动态增强扫描信号特点。方法：对临床及手术病理证实的21例肝脓肿患者MRI平扫及增强后动态扫描资料进行回顾性分析。结果：21例中,单发肝脓肿13例,多发8例,共39个主病灶,15个伴多发子灶。39个主病灶中,＂簇样征＂3个,蜂窝网格状、花边样征24个,＂环靶征＂12个。平扫示主病灶T1WI间隔及壁呈等低信号、脓腔低信号,T2WI间隔及壁略高信号、内脓腔呈更高信号;子病灶中央见点状T1WI低、T2WI高信号;20个主病灶周围见片状或肝段性T2WI高信号。增强后动态扫描：①动脉期肝脓肿27个主病灶分隔及边缘轻度强化,12个主病灶壁轻度强化、其中10个壁边缘明显强化;②门脉期分隔或/和壁强化逐渐明显、壁边缘持续强化,边界更加清晰;③延迟期（1～5min）分隔或/和壁持续强化。30min延迟扫描8个主病灶,壁内层仍见强化,壁边缘强化减退;④子病灶环边缘动脉期轻度强化、门脉期及延迟期强化逐渐明显;⑤主、子病灶坏死脓腔均无强化;⑥28个主病灶周围见片状或肝段性动脉期一过性强化。结论：MRI平扫及动态增强扫描能较好的显示肝脓肿的发生、演变、发展及转归过程,反映肝脓肿的特征表现。     

Targetlike appearance of pseudotumors in segment IV of the liver on sonography.

OBJECTIVE: The purpose of this study is to report a new sonographic appearance of hepatic pseudotumors. These lesions had a targetlike appearance but were caused by spared areas in fatty liver. CONCLUSION: Although representing a frequent pattern in metastases and mycotic abscesses, a central hyperechoic core encircled by a hypoechoic halo has not yet been reported in relation to pseudotumors. Whereas multifocal target lesions in the liver suggest metastases or mycotic abscesses, an isolated target lesion in the fourth hepatic segment requires a differential diagnostic approach and a pseudotumor should be suspected because of its clinical relevance.     

Experiences with grey scale ultrasonography in hepatic amoebiasis

Ultrasound examination was conducted in 151 proven cases of amoebic liver abscess. In the majority of patients the lesion was solitary but 25% of patients had multiple lesions; 17% of all the abscesses were in the left lobe of the liver. Most abscesses had no, or very few internal echoes and these were either of the same density as the normal liver (15%) or less dense (84%). In all cases there were relatively fewer echoes in the lesion. Abscesses in critical areas were accurately located especially in relation to the pericardium. Other liver lesions such as hepatoma which may enter into the clinical diagnosis can be recognised. Ultrasound has particular value in accurate localisation of the lesion for aspiration, demonstration of unsuspected multiple abscesses and size estimation in serial studies of the patient under treatment. The diagnostic errors were mainly due to initial inexperience and demonstrated some of the diagnostic pitfalls. It is concluded that the introduction of this technique has proved to be of considerable value in the diagnosis and management of amoebic liver abscess in our area, where the disease is still a major clinical entity. If diagnosed early and treated adequately the condition has an excellent prognosis.     

Computed tomographic evaluation of an experimental model for pyogenic liver abscesses

Computed tomography (CT) was used to evaluate 15 rabbits with experimentally induced liver abscesses. The animals were examined both before and after intravenous contrast injection. After sacrificing the animals, postfreeze CT scans were made to mark the abdomen for 1-cm thick whole body sections for correlating the gross pathology with the results of the CT scans. CT detected 15 abscesses in 13 of the 14 rabbits with true positive lesions. Ten abscesses less than 1.4 cm in diameter were not detected by CT. Contrast agent enhancement was helpful in 70% of the studies. These abscesses have characteristics similar to human liver abscesses, but there was more gas and calcium in the experimentally induced abscesses than is encountered in humans with hepatic abscesses. The model and its CT characteristics appear well suited for future studies in the diagnosis and treatment of liver abscesses.     

CT of amebic liver abscess

CT findings in 23 patients with amebic liver abscess were analyzed retrospectively. A solitary abscess was present in 17 patients. Five patients had two to five lesions. One patient, a male homosexual, had 15 abscesses. Of the 46 abscesses, 74% occurred in the right lobe. The lesions were generally round or oval. One-half of the abscesses were 2-6 cm in diameter; 11% measured 13-16 cm. An enhancing wall was present in most cases. An incomplete rim of edema was seen in eight abscesses. The margin of the abscess was smooth in 63% and nodular in 37%. Internal septations were noted in 30%. Four patients had focal intrahepatic biliary dilatation peripheral to an abscess. One patient had intraabscess hemorrhage. Extrahepatic abnormalities were present in 18 patients; right pleural effusion (nine), perihepatic fluid collection (five), gastric or colonic involvement (eight), and retroperitoneal extension (one). Gas within an abscess was due to hepatobronchial fistula in one patient and hepatocolic fistula in another. Amebic abscess should be included in the differential diagnosis when CT shows one or more cystic or complex masses in the liver, especially when there is evidence of extrahepatic extension.     

Role of ultrasound in the diagnosis and treatment follow-up of amoebic liver abscess

Sonograms of 48 amoebic liver abscesses (ALA) in 33 patients were retrospectively analysed to determine the frequency of previously described sonographic features. Eighty-five per cent of the ALA were located in the right lobe and 77% of them were contiguous with the liver capsule. ALA were round or oval in 94% of the cases without significant wall echoes (81%). Sixty-two per cent of the abscesses were inhomogeneous. Post-therapy (medical) sonographic follow-up was done in 26 patients with 34 lesions. While 64.7% of the lesions resolved completely, others showed residual abnormalities in the form of hypoechoic (14.7%), mainly hyperechoic (2.9%) and anechoic lesions (17.7%). We conclude that serological and clinical data in combination with these non-specific sonographic features are sufficient for the management of ALA, obviating the need for expensive and invasive techniques in majority of the cases.     

Focal inflammatory diseases of the liver

Inflammatory lesions constitute an important subgroup of focal liver lesions. They may mimic primary or metastatic neoplastic lesions and their differentiation from neoplasia is clinically very important since management of the patient significantly changes. Radiologists should have an important role in both the diagnosis and therapy of these lesions by performing percutaneous aspirations and drainages. In this review we discussed the radiological findings of pyogenic abscesses, amebic abscesses, candidiasis, tuberculosis, hydatic cysts, fascioliasis, ascariasis, schistosomiasis, and sarcoidosis with a special emphasis on US, CT and MR characteristics.     

Gray-scale ultrasonography of hepatic amoebic abscesses.

Retrospective analysis of the ultrasonograms of 42 hepatic amoebic abscesses in 34 patients was performed. All lesions were less echogenic than normal liver. All but 1 were contiguous with the liver capsule and had slight distal sonic enhancement. Twenty-three were predominantly homogeneous with fine, low-level echoes. This pattern is highly suggestive of hepatic amoebic abscess. Nineteen abscesses did not show this pattern and could not be diagnosed based on ultrasonographic criteria.     

肝脓肿的MRI分型和诊断

认识肝脓肿ＭＲＩ典型及不典型征象，探讨ＭＲＩ分型的诊断意义。材料和方法：６７例８２个肝脓肿经手术病理和临床治疗证实，回顾性分析平扫和增强ＭＲＩ表现，并进行归类分型。结果：８２个肝脓肿可分成三种ＭＲＩ类型：房腔型占７１．９５％（５９／８２），特征是病灶体积的２０％以上由液化坏死的房腔和纤维肉芽的腔壁构成；肉芽型占２０．７３％（１７／８２），特征是病灶体积的８０％以上由纤维肉芽组织构成，间以细小液化或     

CT of small pyogenic hepatic abscesses: the cluster sign

Of 36 consecutive patients with pyogenic liver abscesses evaluated by CT, five (14%) had multiple small abscesses less than 2 cm in size. The CT appearance of the small pyogenic abscesses was compared with that of 10 patients who had either fungal or mycobacterial abscesses and with that of 50 patients who had hepatic metastases. In all five patients who had small pyogenic abscesses, the abscesses appeared to cluster, or aggregate, in a pattern that suggested the beginning of coalescence into a single, larger abscess cavity (cluster sign). This cluster appearance was not seen in in any of the patients who had fungal or mycobacterial microabscesses. It was present in only one of the patients who had confirmed hepatic metastasis. Despite the small size of the abscesses, guided needle aspiration was successful in recovering pyogenic organisms in four of the five patients. In our experience, the presence of the cluster sign suggests that the lesions are pyogenic abscesses.     

Solid organizing hepatic abscesses mimic hepatic tumor: Multiphasic computed tomography and magnetic resonance imaging findings with histopathologic correlation

OBJECTIVE: To describe the computed tomography (CT) and magnetic resonance imaging (MRI) findings of solid organizing hepatic abscesses and correlate them with the pathologic findings. METHODS: Ten patients with 10 pathologically proven solid organizing hepatic abscesses who underwent 3-phase CT (n = 10) or MRI (n = 7) were enrolled in this study. Images were retrospectively analyzed by consensus of 2 radiologists for attenuation (signal intensity), shape, and margin of the lesions as well as for their enhancement patterns. Their imaging findings were correlated with their pathologic findings. RESULTS: The main imaging finding on CT or MRI was the well-defined target appearance of a central enhancing area with a low-attenuation (signal intensity) rim on arterial and portal phases. On the delayed phase, most of lesions showed slightly low attenuation (signal intensity) with an enhancing rim, and 1 showed diffuse enhancement. Pathologically, the central areas and peripheral rims corresponded to granulation tissue and fibrosis, respectively. Nine lesions demonstrated a tiny necrotic cystic portion in the center. CONCLUSION: The target appearance of solid organizing hepatic abscesses on CT and MRI can be helpful in differentiating them from other focal liver lesions. These imaging findings are well correlated with the pathologic findings.     

Dual radionuclide subtraction imaging of the spleen

Dual radionuclide subtraction imaging of the spleen using 67Ga citrate and 99mTc is useful in further delineating lesions that are identified on either a routine radiogallium survey or on a conventional sulfur colloid liver-spleen image. Better anatomic localization of left subphrenic abscesses may be obtained. Differentiation of tumors and abscesses from less serious lesions such as cysts, infarcts, and hematomas is possible. We have found this technique to be generally applicable to any organ that can be selectively imaged using a technetium radiopharmaceutical, including the liver, bones, and kidneys. In addition, we are currently evaluating thallium-pertechnetate subtraction imaging in the evaluation of parathyroid adenomata.     

Exophytic spread of hepatobiliary disease via perihepatic ligaments: demonstration with CT and US

Eight cases of hepatobiliary disease located adjacent to or within the perihepatic ligaments (peritoneal reflections surrounding the liver) with exophytic spread along these ligaments (three abscesses from cholecystitis, two bilomas, two hepatic abscesses, and one hematoma from a ruptured hepatocellular carcinoma, with 16 ligamentous lesions: five in the hepatoduodenal ligament, four in the ligamentum teres, three in the falciform ligament, two in the gastrohepatic ligament, one in the transverse mesocolon, and one in the duodenocolic ligament) were studied with sonography and computed tomography. The locations of underlying diseases were the inferior aspect of the left lobe of the liver (three patients), the gallbladder (three patients), and the right hepatic duct (two patients). An understanding of the anatomic detail of the ligamentous attachments of the liver and the continuity of peritoneal ligaments is important in recognizing the ligamentous spread of hepatobiliary disease. This mode of spread of disease should be kept in mind in diagnostic imaging of the abdomen.     

细菌性肝脓肿的低场MRI诊断

目的:探讨低场MRI在细菌性肝脓肿诊断中的临床应用价值.方法:回顾经手术病理或临床治疗证实的19例23个肝脓肿,分析低场MRI平扫及增强影像表现及病理基础.结果:23个肝脓肿14个位于肝右叶,9个位于肝左叶.典型肝脓肿7个,表现环征或双靶征,病灶中心液化坏死,脓肿内小泡状积气或气液平面,病灶周围水肿.不典型肝脓肿16个,不同时期影像表现各异,表现为簇状征,蜂窝征,蜘蛛足征等.结论:低场MRI能较好显示肝脓肿的病理过程中组织结构不同特征,能提高细菌性肝脓肿的诊断正确率.     

Diagnosis and percutaneous treatment of pyogenic hepatic abscesses

Twelve patients with intrahepatic abscesses were examined with computed tomography and ultrasonography between 1979 and 1988. The median size of the lesions was 7 (1-12) cm. They were in 8 patients located only in the right liver lobe and in 3 in both liver lobes. On ultrasonography the echogenicity of the abscesses varied from hypo- to hyperechoic which is consistent with tumours. The final diagnosis of abscess was achieved by fine needle puncture and aspiration for bacterial culture. Nine patients were treated with percutaneous drainage. 3 of them with two catheters, and all received systemic antibiotic treatment. All patients survived the treatment.     

Role of diffusion weighted MR in the discrimination diagnosis of the cystic and/or necrotic head and neck lesions

PURPOSE: The purpose was to determine whether the diffusion weighted imaging (DWI) was able to differentiate necrotic tumor or metastatic lesions from infected necrotic lesions such as abscesses and necrotic lymphadenitis in the neck. MATERIALS AND METHODS: DWI was performed on 37 consecutive patients with 85 head and neck necrotic and cystic lesions. The lesions were classified into four categories: metastatic lymph node involvement including lymphoma, necrotic tumor, abscesses and necrotic lymphadenitis. Each lesion was histopathologically studied and proved. RESULTS: In 12 patients, there were 35 necrotic lymphadenitis (necrotic tuberculosis lymphadenitis, n=18; necrotic nonspecific suppurative lymphadenitis, n=17). Of the 15 necrotic metastatic nodes, 11 lesions were lymphomatous involvement and 4 lesions were other tumor involvement. Other 11 patients have abscesses. Thirteen primary tumoral necrotic lesions arose in the neck of nine patients. All of the abscesses and necrotic lymphadenitis showed hyperintensity on DWI, in contrast to necrotic tumor and necrotic nodal metastasis that showed hypointensity on DWI. DWI successfully differentiated metastatic nodes and necrotic tumors from necrotic lymphadenitis and abscesses. CONCLUSION: DWI may be supportive for differentiating necrotic tumor lesions such as necrotic tumor and metastatic necrotic nodes from the infective necrotic lesions such as necrotic lymphadenitis and abscesses in the head and neck.     

Pyogenic liver abscesses caused by Klebsiella pneumoniae: US appearance and aspiration findings

PURPOSE: To retrospectively compare the ultrasonographic (US) appearance and amount of pus obtained at initial aspiration for liver abscesses caused by Klebsiella pneumoniae with those for liver abscesses caused by other bacterial pathogens. MATERIALS AND METHODS: This study had medical ethics committee approval; informed consent was not required. Asian patients with pyogenic liver abscesses in a 5-year period were included. Abscess clinical, laboratory, and microbiologic characteristics and treatment and outcome were analyzed. US images were classified according to the size of the largest liver abscess, the echogenic pattern of the lesion, the presence of any echogenic debris within the lesion, increased through transmission in the posterior aspect of the lesion, and the lesion margin. Clinical and US characteristics of patients with K pneumoniae monomicrobial liver abscesses and those with non-K pneumoniae monomicrobial or polymicrobial liver abscesses were compared. The chi(2) or Fisher exact test was used for categorical variables; the Student t test was used for continuous variables. RESULTS: There were 120 patients with pyogenic liver abscesses. Median patient age was 69 years (range, 13-94 years). Fifty-nine patients were male, and 61 were female. Fifty patients with K pneumoniae monomicrobial and 33 patients with non-K pneumoniae monomicrobial or polymicrobial liver abscesses underwent US. K pneumoniae monomicrobial liver abscesses were associated with diabetes mellitus (P < .001), higher blood glucose levels at admission (P < .05), predominantly solid US appearances (P < .001), irregular or indistinct lesion margins (P < .05), less than 2 mL of pus aspirated (P < .001), and longer duration of antibiotic treatment (P < .05). CONCLUSION: A predominantly solid appearance at US is associated with K pneumoniae monomicrobial liver abscess. K pneumoniae liver abscess is associated with a much smaller quantity of pus at initial aspiration.     

Pyogenic liver abscess: contrast-enhanced MR imaging in rats

MR imaging was used to evaluate experimentally induced pyogenic liver abscesses in an animal model. Rats were examined before and after IV administration of either gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA), ferrite particles, or both contrast agents together. Pyogenic liver abscesses appeared hypointense on T1-weighted images and hyperintense on T2-weighted images. Bolus administration of Gd-DTPA using a fast spin-echo sequence with repetition time of 250 msec and echo time of 20 msec (SE 250/20) showed transient selective enhancement of normal hepatic tissue and increased lesion conspicuity, quantitatively assessed by the contrast-to-noise ratio, which increased from -35.7 to -59.0. Delayed leakage of Gd-DTPA into the abscess center partially obscured small lesions at 30-60 min. Ferrite particles reduced the signal intensity of normal liver, and the abscess then appeared homogenously hyperintense. Applying the SE 500/32 sequence, the contrast-to-noise ratio increased from -1.2 to +74.0. Coordinated administration of both contrast agents showed a further increase in contrast to +94.0, with a hyperintense abscess rim surrounded by hypointense liver. Gd-DTPA increases abscess-liver contrast by rim enhancement of the abscess wall, and ferrite increases the abscess-liver contrast by selectively decreasing the signal intensity of surrounding normal liver. As a result of increased contrast-to-noise ratio, both contrast agents, alone or in combination, increase the conspicuity of hepatic abscesses.