Journal Club - December 2020 

Changes of ultrasonographic pattern of the spleen examined with a high-frequency linear transducer during growth in puppies 

Research Paper: 

Hwang Y, Noh D, Choi S, Choi H, Lee Y, Lee K. (2020) Changes of ultrasonographic pattern of the spleen examined with a high-frequency linear transducer during growth in puppies. Vet Radiol Ultrasound. 61: 577–582 

In the experience of the study authors, when using a transducer capable of producing frequencies of 12MHz, the splenic parenchyma appeared mottled in puppies but not in adult dogs. The authors hypothesised that the ultrasonographic pattern of the splenic parenchyma using high-frequency transducer gradually changes to a reticulonodular pattern, and after the appearance of the most marked reticulonodular pattern, the pattern of the splenic parenchyma gradually changes to a granular pattern again during growth in a normal puppy. 

The study purpose was to describe the changes in the ultrasonographic pattern of the spleen examined with a high-frequency linear array transducer during growth in normal puppies. 

Study Design: 

• Prospective, longitudinal, descriptive study 
• The study population was nine healthy dogs, each from different litters (4 beagles and 5 mixed breeds) 
• All the puppies were on a strict worming regime and were vaccinated 

• Transabdominal ultrasound was performed every 4 weeks from 4 weeks of age to 60 weeks of age 
• Prior to ultrasound exam each puppy had a physical exam including weight, body condition score and temperature assessment 
• Each puppy was fasted for 4hrs prior to ultrasound examination but was allowed free access to water 
• One clinician performed the ultrasound examination using a 12MHz linear array. The ultrasound machine settings were kept constant for each examination 

Images and videos of the splenic head, body, and tail were obtained on transverse and longitudinal views with the videos used to subjectively evaluate the % of the spleen involved. The Images were evaluated 3 times and graded by 2 observers based on consensus. The grading system for the splenic parenchyma can be seen in the table below: 

Results: 

Paired t-tests were used to compare the difference between grades at different ages, ap-value of <.05 was considered statistically significant. Scatter plots were created to show the association between grade and age. 

• During the study none of the puppies received medication or showed clinical signs of any condition that may have affected the lymphoid system 

• The grade of the splenic parenchyma was significantly different between 4 and 16 weeks (P < 0.001), between 16 and 32 weeks (P = 0.007), between 32 and 48 weeks (P < 0.001), and between 48 and 60 weeks (P = 0.003) 
• In all puppies the grade of the splenic parenchyma increased, then decreased again 
• All puppies were observed as grade 1 at 4 weeks old 
• Over weeks 8 - 24 the grade increased with the most marked pattern at 28 - 36 weeks 
• From 40 - 56 weeks the grade decreased until all puppies had a grade 1 pattern at 60 weeks 

Discussion: 

The study findings supported the authors hypothesis - the ultrasonographic pattern of the splenic parenchyma using high-frequency transducer gradually changes to a reticulonodular pattern, and after the appearance of the most marked reticulonodular pattern, the pattern of the splenic parenchyma gradually changes to a granular pattern again during growth in a normal puppy. 

Considering previous studies in children and the similar structure of human and canine spleens, the authors suggest that the hypoechoic nodules seen in spleen when using high frequency ultrasound transducers represent the lymphoid follicles within the white pulp. 

Limitations: 

This study only used a small number of puppies and results should be interpreted with caution. Larger studies with greater numbers and a wider range of breeds would be needed in further studies.  

As histologic evaluation of the spleens was not carried out, subclinical disease effecting the lymphoid system cannot be ruled out. 

Clinical Relevance: 

As ultrasound technology improves and transducers capable of higher frequencies become more widely available, it is important that normal changes in organs revealed by improved technology are not misinterpreted as signs of disease. 

Current texts will usually describe the spleen as homogenous with an echogenic granular pattern, and a reticulonodular pattern, such as that seen in the puppies in this study, is usually described in cases of pathology such as lymphoma or mast cell tumour. This study is important in revealing that the reticulonodular pattern can be a normal feature and should not be interpreted as indicating a pathological condition.