Diagnostic ultrasonography in cattle with abdominal fat necrosis

Abstract

This study describes the ultrasonographic findings in 14 cows with abdominal fat necrosis. Ultrasonography of the abdomen revealed the presence of heterogeneous hyperechoic masses and hyperechoic omentum with localized masses floating in a hypoechoic peritoneal fluid. A hyperechogenic rim was imaged around both kidneys. The intestines were coated with hyperechoic capsules and the intestinal lumens were constricted. Ultrasonographic examination of the pancreatic parenchyma showed an overall increased echogenicity which was homogenously distributed in 3 cases. A diagnosis of abdominal fat necrosis was made with ultrasound-guided biopsy of the echogenic masses, and thereafter at postmortem examination. Results from this study demonstrate the efficacy of ultrasonography as an imaging modality for antemortem diagnosis of abdominal lipomatosis in cattle. To the authors’ knowledge, this study is the first that illustrates ultrasonographic findings in cattle affected with abdominal lipomatosis.

Introduction

Necrosis of mesenteric or other abdominal or retroperitoneal fat is a common finding in domestic animals and humans (1). The pathogenesis is poorly understood but there appears to be a number of causes. In humans, the condition may be encountered following localized trauma to fat tissue as a complication of pancreatitis (2). In domestic animals, the condition is usually attributed to the liberation of pancreatic enzymes in pancreatitis, pressure and trauma, febrile conditions, grazing on tall fescue grass, rapid cachexia, or genetic predisposition (1–3). Excessive fattiness of abdominal adipose tissue in the growing stage and subsequent disturbances in lipid metabolism are also related to the occurrence of fat necrosis in cows (4). The composition of the fatty deposits is identical with the fat of normal cows, and there is no suggestion that the disease is neoplastic (3). Prognosis for cattle affected with fat necrosis is highly variable. In some cases, the disease is an incidental finding (5) that has no impact on health but in some cases the prognosis is hopeless and the affected cow is salvaged (3,6).

Abdominal fat necrosis may be discovered incidentally during an attempt at rectal examination which may fail because of the stricture of the rectum due to perirectal fat necrosis (7). Transrectally, the disease is characterized by the presence of hard masses of various sizes and shapes located in the mesentery of the spiral colon, mesorectum, and perirenal tissues (8,9). Abdominal fat necrosis can also be infrequently diagnosed in cattle during laparotomy to replace displaced abomasum, during exploratory laparotomy, or when performing a cesarean section. In every case, firm masses are palpated in the abdominal fat during the surgical procedure (5). The differential diagnosis includes lymphosarcoma, intestinal adenocarcinoma, abdominal abscesses, developing or mummified fetuses, and peritoneal tumors such as mesothelioma (3).

In valuable cattle with severe clinical signs due to the disease, ultrasound examination and ultrasound-guided biopsy to confirm fat necrosis can be of value to avoid an exploratory laparotomy and to salvage the cow if the prognosis is poor. To the authors’ knowledge, ultrasonographic diagnosis of lipomatosis in cows has not been reported. This study was therefore designed to describe the ultrasonographic findings in cattle with abdominal lipomatosis and to confirm the diagnosis antemortem using a free-hand, ultrasound-guided biopsy technique.

Materials and methods

Animals, history, clinical and postmortem examinations

Fourteen cows aged 4 to 8 y and weighing 390 to 540 kg were examined in this study. Nine were examined at the Veterinary Teaching Hospital, Rakuno Gakuen University, Hokkaido, Japan, during 2000 to 2004. Three cows were examined at Zagazig University, Veterinary Teaching Hospital, Egypt, between 2004 and 2007 and 2 cows were examined at Qassim University, Veterinary Teaching Hospital, Saudi Arabia, between 2008 and 2010. All animals underwent a thorough clinical examination as described previously (10,11), which included general behavior and condition, auscultation of the heart, lungs, rumen, and intestine, measurement of heart rate, respiratory rate, and rectal temperature, swinging auscultation, percussion auscultation of both sides of the abdomen, and rectal examination. Based on the owners’ decision, the animals were not treated, and therefore scheduled for necropsy when a confirmed diagnosis was made. Ten cattle were categorized as healthy, based on the clinical examination and laboratory variables, and therefore enrolled in the study as controls.

Hematological and biochemical analyses

Blood samples were collected from the controls and diseased cattle by puncture of the jugular vein. Hematocrit, hemoglobin, total and differential leucocytes were determined from samples of blood with ehtylenediamine tetra-acetic acid (EDTA) using an automated veterinary hematological analyzer (Vet Scan HM5; Abaxis, Budapest, Hungary). After centrifugation of a second blood sample, serum was collected and frozen for subsequent biochemical analyses. Commercial kits were used to determine the serum concentrations of total protein, albumin, calcium, phosphorus, total bilirubin, total cholesterol, triglycerides, phospholipids, free fatty acids (FFA), glucose, urea nitrogen, creatinine, β-hydroxy butyric acid (BHBA), sodium, potassium, and chloride. The serum activities of aspartate aminotransferase, γ-glutamyl transferase, pancreatic amylase, lipase, creatine kinase, and lactate dehydrogenase (LDH) were also measured. An automated biochemical analyzer (Biosystems A15, Barcelona, Spain) was used for measurement of all serum parameters. Serum protein fractions were determined by electrophoresis.

Ultrasonographic examination

As described previously (12–14), abdominal and thoracic ultrasonography were carried out while the animals were standing, using 3.5 and 5.0 MHz transducers (Model EUB-26; Hitachi Co., Tokyo, Japan; Pie Medical 240 Parus, The Netherlands; SSD-500, Aloka, Tokyo, Japan). In preparation for ultrasonography, the intercostal spaces and the entire abdomen were clipped, shaved, and swabbed with alcohol, and coupling gel was finally applied. To obtain adequate restraint, cows were lightly sedated with xylazine (0.04 mg/kg body weight, intravenously). The heart and its major blood vessels, lungs, pleura, mediastinum, peritoneum, rumen, reticulum, omasum, abomasum, spleen, small and large intestines, liver, pancreas, and right kidney were examined transcutaneously. The left kidney and urinary bladder were examined transrectally. The pancreas was imaged as previously reported (15). The right lobe and body of the pancreas were imaged between the right 10th to 12th intercostal spaces. However, because of its dorsomedial location, the left lobe could not be visualized (16).

Ultrasound-guided biopsy

The biopsy of the fat masses was carried out as described previously (12,16). Briefly, after standard surgical disinfection, the area was infiltrated with 10 mL procaine HCl 2%. Ten minutes later, a small incision was made with the point of a scalpel blade immediately adjacent to the transducer through the skin in either the abdominal or thoracic wall. A 14G × 150 mm spinal biopsy needle (Kurita Co., Tokyo, Japan) was introduced and sonographically guided toward the mass. The plain stylet was then withdrawn and a forked stylet inserted and pushed in a further 1–2 cm in a twisted fashion. Both the needle and forked stylet were then removed with a sample of the lesion. Immediately after biopsy, the samples were fixed in 10% neutral buffered formalin and subsequently embedded in paraffin, sectioned at 4 μm, stained with hematoxylin and eosin, and examined by light microscopy.

Statistical analysis

Data are presented as means ± standard deviation and the analysis was conducted using SPSS program, version 16.0 (IBM, Armonk, New York, USA). Hematological and biochemical data were compared between diseased and control cattle, using Student’s t-test. The level of significance was set at P < 0.05.

Results

Clinical, hematological, and biochemical findings

Of the 14 cattle, 7 were Japanese black, 4 were Holsteins, 2 were Friesian, and 1 was Holstein-Friesian. Five cows were pregnant and 9 were non-pregnant. The cattle had been ill for 2 to 6 wk before they were admitted with a history of anorexia, decreased milk production, long-standing diarrhea, attacks of moderate abdominal pain, and passage of small amounts of feces. The most noticeable clinical presentations were anorexia in 11 cows, decreased milk production in 7, long-standing diarrhea in 6, attacks of moderate abdominal pain in 4 and passage of small amounts of feces in 5 cows. Compared with the controls, complete blood cell count identified a neutrophilic leukocytosis (P < 0.05) in 10 animals. Abnormalities identified from the chemistry profile included elevated total serum proteins (P < 0.05) in 6 cows, hyper <-globulinemia (P < 0.01) in 9, decreased concentration of phospholipids and total cholesterol (P < 0.01) and elevated concentration of FFA and BHBA (P < 0.01) in 7 and elevated serum activities of LDH (P < 0.01) in 4 cows. Compared to controls, other measured serum parameters did not differ significantly.

Ultrasonographic findings

Of the 14 cows with fat necrosis, ultrasonography was valuable in detecting lesions in 13 (93%) cases by either transcutaneous or transrectal examination. In 1 cow, transcutaneous examination revealed nothing abnormal and transrectal examination was impossible because of the severe narrowing of the rectum. Transcutaneous abdominal ultrasonography of the right flank revealed the presence of heterogeneous hyperechoic masses in 6 cows (Figure 1A). In these cows, transrectal examination by ultrasonography revealed nothing valuable, and in 2 of them, rectal examination was impossible because of the detected narrowing of the rectum. In 7 cows transrectal examination showed hyperechoic omentum with localized, non-capsulated masses floating in a hyperechoic peritoneal fluid (Figure 1B). In 5 of the latter cases, rectal examination was very difficult. In 4 of the cases, the left kidney was scanned and hyperechoic surrounding masses were imaged. The right kidney was imaged directly in the right flank or through a diagonal transhepatic window in the 12th intercostal space. A hyperechogenic rim (diameter of 6.7 ± 3.9 cm) was imaged around the kidneys in 8 cows. The cortex and medulla were not easily differentiated in any of these cows (Figure 2). The jejunum was imaged at the right ventral abdomen and the duodenum in the 9th to 11th intercostal spaces. The intestinal loops were coated with a hyperechoic capsule and their lumens were restricted in 5 cows (Figure 3).

Figure 1.

Ultrasonograms in 2 cows with fat necrosis. Echogenic masses are visualized within the omentum. Image A was taken transabdominally from the right flank, while image B was taken during transrectal examination. FN — fat necrosis masses; PF — peritoneal fluid.

Figure 2.

Ultrasonogram in a cow with fat necrosis. Echogenic masses are visualized around the kidney. Images were taken from the 12th intercostal space on the right side. 1 — fat necrosis masses; 2 — cortex and medulla; 3 — renal sinus.

Figure 3.

Ultrasonograms in a cow with fat necrosis. Echogenic masses are visualized around the duodenum. The duodenal wall is severely thickened. Images were taken from the 9th intercostal space on the right side. D — duodenum; L — liver; FN — fat necrosis masses.

Ultrasound-guided biopsy

Transcutaneous ultrasound-guided biopsy of fat necrosis lesions was possible in 8 cows in which lesions were detected through the right flank or around the right kidney. Histologically, biopsy specimens showed only extensive areas of coagulative necrosis of adipocytes that contained foci of saponification. It was not possible to carry out the procedure in the 7 cows in which lesions were detected only transrectally. In 3 of the biopsied cows, compared to the normal imaging textural pattern of the pancreas, the pancreatic parenchyma showed an overall increased echogenicity which was homogenously distributed throughout the organ (Figure 4). Differential diagnosis in these cases included acute pancreatitis. Microscopic examination of pancreatic specimens revealed diffuse and extensive infiltration of giant fat cells within the pancreatic parenchyma that were separated and surrounded by bands of mature fibrous connective tissue. Inflammation was not a prominent feature. No scanning abnormalities were detected while imaging the heart and its major blood vessels, lungs, pleura, mediastinum, rumen, reticulum, omasum, abomasum, and spleen.

Figure 4.

Pancreatic ultrasonogram in a cow with abdominal fat necrosis. An overall pancreatic hyperechogenicity is apparent. Images were taken in the right 11th intercostal space with a 3.5 MHz linear transducer. 1 — liver; 2 — pancreas.

Postmortem findings

In the 14 cows with fat necrosis, collected lesions at necropsy weighed 7 to 15 kg (12 ± 2 kg). In 10 cases, hard necrotic fat masses were found surrounding the duodenum, jejunum, ileum, cecum, colon, and rectum. A transverse section through the affected intestines revealed severely constricted lumens. In 12 cows, the omentum was thick with presence of necrotic fat masses throughout. In 8 cows, both kidneys were coated with hard masses of necrotic fat (Figure 5). As detected antemortem, on histological examination of the fat necrotic masses, there were extensive areas of coagulative necrosis of adipocytes that contain foci of saponification. Inflammation was not a prominent feature.

Figure 5.

Postmortem findings in a cow with abdominal fat necrosis. Image A shows necrotic fat masses surrounding the small intestine while image B shows necrotic fat masses surrounding the kidney.

Discussion

To the best of the authors’ knowledge, this study is the first to address the ultrasonographic findings in cattle with abdominal lipomatosis. Fat necrosis, or lipomatosis, is a clinical entity described in several species (9,17–20). Cases of abdominal fat necrosis are usually sporadic but there are reports of herd prevalence as high as 67% when tall fescue toxicosis is present (21). The disorder causes a variety of clinical syndromes such as intestinal stenosis, urinary retention, dystocia, and infertility (1,18). Small areas of fat necrosis can be discovered when performing routine right flank laparotomy (5). In domestic animals, abdominal lipomatosis is often associated with pancreatitis (22); however, pancreatitis is a rare condition in cattle (15). None of the 14 cows in this study had pancreatitis. This was supported antemortem by the normal serum activities of pancreatic amylase and lipase and by the pancreatic ultrasonograms. Definitive diagnosis was made after examination of pancreatic biopsy specimens in the 3 cows with increased pancreatic echogenicity.

In this study no historical, physical, or laboratory abnormalities were helpful in making a diagnosis in the cattle with abdominal fat necrosis. Results of a serum lipid profile pointed to the presence of a disturbance of lipid metabolism but the serum activities of amylase and lipase were within reference ranges. In agreement with a previous study (8) the serum concentrations of total cholesterol, triglycerides, and phospholipids were lower than the control data, while the serum concentration of FFA was higher. The serum concentration of cholesterol was also low in cattle fed tall fescue (21).

In contrast with the hematological and biochemical findings, the ultrasonographic results were helpful for diagnosing lesions of abdominal fat necrosis. Ultrasonographic examination determined the extent of the fat necrosis lesions around the right kidney, intestines, and within the pancreas and the omentum. Both transcutaneous and transrectal ultrasonography revealed the presence of heterogeneous hyperechoic masses. However, ultrasonography alone cannot ensure an accurate diagnosis and a differential diagnosis must include lymphosarcoma, intestinal adenocarcinoma, and peritoneal tumors such as mesothelioma (3).

A free-hand biopsy technique with ultrasound guidance was used in 8 cows (12,16). This was accomplished by holding the transducer with one hand while inserting the needle with the other. It enabled good visualization of the needle and it entered at an oblique angle to the long axis of the transducer. The procedure requires more experience than using a biopsy needle guide. The user should pay attention not only to ultrasound anatomy, but also to hand–eye coordination and confidence that the needle will not only pass at an appropriate angle, but also remain within the plane parallel with the ultrasound beam. There was a definite learning curve, but once mastered, the technique was relatively straightforward. If the needle cannot be seen during ultrasonography, moving the transducer slightly into the path of the needle, gently agitating the needle or injecting air or microbubbles in saline solution through the needle usually allows the needle’s position to be determined (15,16).

In the normal cow, the echogenic pattern of the pancreas is homogeneous and it is slightly hyperechoic compared to the liver parenchyma (16,23). One of the most interesting sonographic findings reported here was pancreatic lipomatosis. The ultrasonographic pattern of the pancreatic parenchyma here was hyperechogenic and homogenously distributed over the entire pancreas. The fat echogenicity is higher than normal parenchymal echogenicity as in cases of fatty deposits in the liver (24). Acute pancreatitis was excluded by histopathologic examination of biopsy specimens and by the normal activities of serum amylase and lipase. Although histological examination of the pancreas showed atrophy of pancreatic acini, pancreatic enzymes remained within reference ranges. It was shown previously in cows with experimentally induced pancreatitis that the serum amylase and lipase concentrations appear to be of little value in diagnosing bovine pancreatitis. Elevations may be used in support of a diagnosis, but evidence indicates that they cannot be used as a standard for a definitive diagnosis, at least for experimentally induced pancreatitis (15).

This study showed that ultrasonography can be used as an effective noninvasive tool to lead to a diagnosis of potential abdominal fat necrosis in cattle. Ancillary procedures, such as ultrasound-guided biopsy and histological examination of biopsy specimens are required for the antemortem verification of abdominal fat necrosis in cattle and may avoid exploratory laparotomy in cases with a perceived poor prognosis.