1887

Spleen

image of Spleen
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Abstract

The spleen is an elongated, strap-like organ located adjacent to the left mid-abdominal wall, typically aligned in a dorsocranial-ventrocaudal plane. In dogs without hepatomegaly or gastric distension, the head of the spleen is usually located deep to the 11th-13th ribs, cranial to the left kidney, and is often seen to fold medially on to itself. In cats, the entire spleen is usually visible just deep to the left mid-abdominal wall, and the head of the spleen may be partly obscured by the 12th-3th ribs. This chapter looks at indications and the value of ultrasonography compared with radiography and computed tomography. Imaging technique and normal ultrasonographic appearance are explained. Diffuse parenchymal disease, focal parenchymal disease, splenic torsion and particular considerations for sampling are covered. This chapter contains five video clips.

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Figures

Image of 9.1
9.1 CT image showing the location of the canine spleen along the left abdominal wall. The head can be seen to fold on to itself and the tail passes along the floor of the abdomen towards the right side. CT image showing the location of the feline spleen along the left abdominal wall. The head of the spleen is partly overlain by the 13th rib.
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9.2 Lateral abdominal radiograph of a mid-abdominal mass showing displacement of intestines cranially, dorsally and caudally. The primary differential diagnosis for this would be a splenic mass.
Image of 9.3
9.3 Ultrasonograms of the head of the spleen. Intercostal approach with the probe aligned parallel to the ribs: the spleen is seen folding on to itself. Transverse imaging plane: the tip of the head of the spleen is difficult to view and there is shadowing by an overlying rib.
Image of 9.4
9.4 Ultrasonograms of a section through an enlarged canine spleen affected with lymphoma using different transducers. 5 MHz curvilinear probe. The spleen has a variable echogenicity throughout and is less echogenic than a normal spleen. 8 MHz microconvex probe. Numerous small hypoechoic nodules that were not clearly seen in (a) are now visible. 15 MHz linear probe. The hypoechoic nodules are much more clearly seen and appear to be greater in number than in (b).
Image of 9.5
9.5 The normal feline spleen has a fine evenly granular appearance. The normal canine spleen has a fine evenly granular appearance. The hyperechoic line seen along the distal border of the spleen is the splenic capsule, which is at right angles to the beam in this region. In many normal dogs the splenic parenchyma is more echoic than the liver.
Image of 9.6
9.6 Hyperechoic invaginations along the splenic hilus are typical of myelolipidosis and are not felt to be clinically significant.
Image of 9.7
9.7 Ultrasonograms of a dog with immune-mediated haemolytic anaemia and a packed cell volume of 0.17. Hyperechoic blood within a branch of the splenic vein (arrowed). The vessel is not clearly seen until demonstrated with colour Doppler. Colour Doppler identifies the branch of the splenic vein not readily seen in (a).
Image of 9.8
9.8 Ultrasonogram of an 8-year-old Rottweiler with a distal femoral osteosarcoma showing a rounded mass (between the callipers) deep to the spleen, most of which is isoechoic to the spleen. Fine-needle aspiration of the mass confirmed that this was accessory splenic tissue.
Image of 9.9
9.9 Ultrasonogram of a 5-year-old Springer Spaniel with immune-mediated anaemia showing a moderate degree of generalized splenomegaly without alteration of the parenchymal appearance.
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9.10 Ultrasonogram of a dog that developed a hyperechoic spleen with a diffuse granulonodular appearance to its parenchyma. The spleen was not significantly enlarged. Cytology of a fine-needle aspirate confirmed the presence of lymphoma.
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9.11 Hypoechoic splenic mass containing several small hyperechoic flecks (arrowed) indicating the presence of gas. Colour Doppler shows blood flow around but not within the mass. The mass was confirmed as a splenic abscess.
Image of 9.12
9.12 Large hypoechoic mass in a canine spleen containing several anechoic areas representative of intralesional haemorrhage. The mass had a histopathological diagnosis of haemangiosarcoma. Large mixed echogenic mass in a canine spleen containing a small amount of intralesional haemorrhage. The mass had a histopathological diagnosis of benign haemangioma. Large mixed echogenic mass in a canine spleen with a histopathological diagnosis of benign nodular hyperplasia. Large mixed echogenic mass in a canine spleen with a histopathological diagnosis of histiocytic sarcoma.
Image of 9.13
9.13 Ultrasonogram of a bulging nodule (between the callipers) that was isoechoic to the remainder of the cat’s spleen. The mass had a cytological diagnosis of lymphoma.
Image of 9.14
9.14 Canine spleen containing numerous variably sized hypoechoic nodules scattered throughout the parenchyma. Cytological diagnosis was lymphoma. Canine spleen containing numerous variably sized nodules scattered throughout the parenchyma, which range in appearance from hypoechoic to target-type nodules. Cytological diagnosis was metastatic carcinoma secondary to an anal sac tumour.
Image of 9.15
9.15 Small solitary canine splenic nodule with the appearance of a target lesion (between the callipers). Note the hyperechoic core and hypoechoic rim. Cytological diagnosis was nodular hyperplasia.
Image of 9.16
9.16 Hypoechoic nodule (arrowed) in the spleen of an elderly dog. Two hyperechoic nodules (arrowed) in the spleen of an elderly dog. Mixed echogenic nodule (arrowed) in the spleen of an elderly dog. All of these lesions were diagnosed as nodular hyperplasia on fine-needle aspirate cytology.
Image of 9.17
9.17 Ultrasonogram of a 2 cm diameter mass in a cat with immune-mediated haemolytic anaemia. The mass is isoechoic to the remainder of the spleen. Fine-needle aspirate cytology diagnosed the mass as a focal region of extramedullary haemopoiesis. Small hypoechoic nodule representing a focal area of extramedullary haemopoiesis. Mixed echogenic splenic mass (*) diagnosed as a focal area of extramedullary haemopoiesis on fine-needle aspirate cytology.
Image of 9.18
9.18 Ultrasonogram of a canine spleen showing the demarcation line between the normal hyperechoic spleen (to the left of the image) and the hypoechoic infarcted spleen (to the right of the image). Hyperechoic flecks within the infarcted area give it a ‘starry sky’ appearance. Colour flow Doppler assessment shows flow in the normal hyperechoic splenic tissue, but no flow in the infarcted hypoechoic region of spleen.
Image of 9.19
9.19 Ultrasonogram of a large spleen showing the ‘starry sky’ appearance of thrombosis. A laparotomy was performed and splenic torsion was confirmed as the underlying cause.
Image of 9.20
9.20 The splenic vein of this dog with hyperadrenocorticism was thrombosed. The colour flow Doppler shows recanalization of the vein with flow around and through the thrombus.

Supplements

Normal spleen in a cat.

This clip was recorded during the ultrasonographic examination of the cranial abdomen in an elderly cat presented for hyperthyroidism. The spleen is a small, well defined structure lying superficially, with the gastric fundus lying just deep to it. The splenic parenchyma is homogeneous except for a focal echogenic lesion seen towards the tail of the spleen. This was considered unlikely to be of clinical significance. (Courtesy of F. Barr)

Normal spleen in a dog.

The transducer has been placed on the ventral abdominal wall in a left paramedian position in this medium-sized crossbred dog. At the start of the clip, the tip of a liver lobe is seen superficially on the left of the screen, with the head of the spleen lying adjacent to it on the right. Note that the splenic parenchyma is more echogenic and more closely textured than that of the liver. The gastric fundus lies just deep to the liver and spleen. As the clip progresses, the transducer is moved caudally over the body of the spleen, showing a large vein at the splenic hilus. (Courtesy of F. Barr)

Splenic infarction (1).

A 7-year-old crossbred dog with immune haemolytic anaemia, which developed abdominal distension and tachypnoea. This clip shows a small volume of free abdominal fluid surrounding the head of the spleen, superficially and to the left of the screen. As the transducer is moved caudally, the tail of the spleen is seen to be mildly expanded and relatively hypoechoic to the remainder of the organ. (Courtesy of F. Barr)

Splenic infarction (2).

Same dog as in Splenic infarction (1). This clip, using Power Doppler, shows good perfusion in the main part of the spleen. (Courtesy of F. Barr)

Splenic infarction (3).

Same dog as in Splenic infarction (1). This clip, also using Power Doppler, shows no detectable blood flow in the expanded, hypoechoic tail of the spleen, supporting the presumptive diagnosis of splenic infarction. (Courtesy of F. Barr)

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