Point-of-Care Ultrasound Techniques for the Small Animal Practitioner. Группа авторов

fluid scoring system determined using abdominal focused assessment with sonography for trauma in 101 dogs with motor vehicle trauma. J Vet Emerg Crit Care 19(5):426–437.

Chapter Nine POCUS: Spleen

      Stephanie C. Lisciandro and Sarah Young

Introduction

      The POCUS examination of the spleen is a valuable diagnostic tool for guiding clinical care and, with adequate care and awareness, can be effectively performed by a nonradiologist veterinarian. The POCUS spleen examination is not meant to replace a complete detailed abdominal ultrasound study by a veterinarian with advanced training (the veterinary radiologist or internist) but rather serves as a screening test for obvious abnormalities. Ultrasonographic findings involving the spleen may be subjective and nonspecific, including splenic size and generalized changes in echogenicity. Additionally, the frequent close anatomical contact of the spleen and liver can make it difficult to differentiate the origin of a mass, particularly for a less experienced sonographer.

      As stated in Chapter 8, a concurrent AFAST examination should be performed with any of the POCUS abdominal organ examinations to rule out intraabdominal, retroperitoneal, pleural and pericardial effusions, and in the case of the POCUS spleen examination, to rule out splenic hemorrhage. The AFAST not only detects free peritoneal fluid but also semiquantitates its volume using its abdominal fluid scoring system and assigning an abdominal fluid score (see Chapter 6). The abdominal fluid score helps predict the degree of anticipated anemia in cases of hemoabdomen (Lisciandro 2011; Lisciandro et al. 2009). Global FAST is an even better approach to survey for pleural and pericardial effusion, cardiac and pulmonary abnormalities, and patient volume status. Moreover, Global FAST is used as a screening test to rapidly discriminate between localized versus disseminated disease, comorbidities, and complications, which may be especially helpful in hemoabdomen cases.

       What the POCUS Spleen Can Do

       Identify focal or multifocal splenic masses or nodules.

       Identify parenchymal changes by screening for changes in echogenicity associated with diffuse splenic diseases.

       Identify splenic infarction and thrombosis.

       Help the clinician to recognize splenic torsion.

       These last three goals are inherently more difficult for the novice sonographer and abnormalities should prompt referral for a complete detailed abdominal ultrasound examination.

       What the POCUS Spleen Cannot Do

       Differentiate benign from malignant splenic masses. The Global FAST approach is a rapid add‐on assessment screening test for localized versus disseminated disease through surveying the abdomen (AFAST), the thorax (TFAST) including heart (TFAST), and lung (Vet BLUE) as well as for detecting other comorbidities.

       Definitively diagnose diffuse and localized splenic conditions based on echogenicity.

       Reliably determine splenic size (large or small) in dogs (more reliable for size in cats).

       Indications

       Cranial organomegaly or pendulous abdomen.

       Abdominal pain.

       Abdominal trauma.

       Hematological disorders such as anemia or thrombocytopenia.

       Generalized lymphadenopathy.

       Episodes of collapse, lethargy or vomiting.

       Objectives

       Recognize splenic masses (single, multifocal).

       Recognize regional and diffuse changes in splenic echogenicity.

       Recognize splenic venous congestion, thrombosis, and infarction.

       Recognize splenic torsion.

Patient Positioning and Probe Selection

      A curvilinear (microconvex) probe is most frequently used to image the spleen, and the MHz is adjusted for the size of the animal. Smaller dogs and cats are generally imaged using higher frequencies of 7.5–10 MHz (less penetration, better detail) and large dogs are generally imaged using lower frequencies such as 5 MHz (deeper penetration, less detail). In small dogs and cats, a linear probe may also be used in order to maximize image quality (due to the higher resolution) when greater penetration depth is not of concern.

      Patients are most commonly imaged in dorsal recumbency. In large dogs, however, the cranial aspect of the spleen is often located under the ribcage on the left side. Repositioning these patients into right lateral recumbency allows visualization of the cranial aspect or head of the spleen using a left intercostal approach (Hecht 2008). The authors recommend performing a Global FAST to screen for any intrathoracic problems including pleural and pericardial effusion, cardiac and pulmonary conditions, and abnormal volume status that may pose patient risk before moving the patient into dorsal recumbency.

How to Perform the POCUS Spleen

      The patient is placed in dorsal recumbency, the abdomen is shaved, and acoustic coupling gel is applied for best visualization. Although image quality will be diminished, ample application of 70% isopropyl alcohol to haired skin can be utilized in an emergency situation. The spleen is located caudal to the stomach on the patient’s left side and can provide an acoustic window for the left kidney (see also Figures 6.18, 16.3, 16.4, 16.5). The spleen is identified by its hyperechoic (bright white) capsule and blood supply splitting its capsule, unlike the liver. Spleen position and size vary between patients and with the degree of gastric filling. The entire length of the spleen is generally not visualized in one acoustic window and so its entirety must be traced cranially to the head of the spleen and caudally to its tail.

The position of the spleen may vary between patients. The head or cranial aspect of the spleen is generally located on the left side caudal to the last rib. In large dogs, it may be located under the ribcage and therefore, repositioning into right lateral recumbency with a left intercostal approach may be necessary. The spleen is then traced caudally toward its hilus where the splenic vein is imaged and seen branching in a “Y” configuration, referred to by some sonographers as the “whale tail” shaped like the tail fluke (Figure 9.1; see also Figures 39.8 and 39.9). Splenic arteries are usually not visualized (Hecht 2008). Evaluation of the spleen continues as the sonographer follows the spleen distally along the left side of the abdomen to examine the caudal aspect of the spleen to its tail so that the entire organ has been examined. Remember that the spleen is anchored at the head by its short gastric vessels along the greater curvature of the stomach but has a relatively mobile tail. In some patients, the tail of the spleen may be located medial and to the right side of the patient instead of the left. Several sweeps along the length and width of the spleen may be necessary for a thorough interrogation, especially in animals with splenomegaly.

      Pearl: Identify the spleen by its hyperechoic (bright white) capsule and blood supply splitting its capsule, unlike the liver.

Ultrasonographic Findings in a Normal Spleen