Multi-factorial considerations for intra-thoracic lymph node evaluations of healthy cats on computed tomographic images

Abstract

Background: It is difficult to examine mild to moderate feline intra-thoracic lymphadenopathy via and thoracic radiography. Despite previous information from computed tomographic (CT) images of intra-thoracic lymph nodes, some factors from animals and CT setting were less elucidated. Therefore, this study aimed to investigate the effect of internal factors from animals and external factors from the CT procedure on the feasibility to detect the intra-thoracic lymph nodes. Twenty-four, client-owned, clinically healthy cats were categorized into three groups according to age. They underwent pre- and post-contrast enhanced CT for whole thorax followed by inter-group evaluation and comparison of sternal, cranial mediastinal, and tracheobronchial lymph nodes.

Results: Post contrast-enhanced CT appearances revealed that intra-thoracic lymph nodes of kittens were invisible, whereas the sternal, cranial mediastinal, and tracheobronchial nodes of cats aged over 7 months old were detected (6/24, 9/24 and 7/24, respectively). Maximum width of these lymph nodes were 3.93 ± 0.74 mm, 4.02 ± 0.65 mm, and 3.51 ± 0.62 mm, respectively. By age, lymph node sizes of these cats were not significantly different. Transverse lymph node width of males was larger than that of females (P = 0.0425). Besides, the detection score of lymph nodes was affected by slice thickness (P < 0.01) and lymph node width (P = 0.0049). Furthermore, an irregular, soft tissue structure, possibly the thymus, was detected in all juvenile cats and three mature cats.

Conclusions: Despite additional information on intra-thoracic lymph nodes in CT images, which can be used to investigate lymphatic-related abnormalities, age, sex, and slice thickness of CT images must be also considered.

Keywords: Cat; Computed tomography; Lymph node; Slice thickness; Thorax; Thymus.

Fig. 1

The comparative effect of gender (a) and gonadal status (b) on the body weight and the effect of gonadal status on body condition score (c) (asterisk: significant differences were detected)

Fig. 2

The soft tissue window (window width: 350 Hounsfield Unit (HU) and window level: 40 HU), transverse computed tomographic post-contrast image of feline thorax indicated the sternal lymph node (white dash line; a) the cranial mediastinum lymph node (white dash line; b), the tracheobronchial lymph node (white dash line; c), and suspected thymus (asterisk; d)

Fig. 3

The presence of intra-thoracic lymph nodal hilus fat on each plane of transverse, sagittal or dorsal computed tomographic image. The nodal hilus fat was scored as 0, no evidence of nodal hilus fat (a, b, c); 1, evidence of nodal hilus fat but intranodal fat outline was not distinct (d, e, f); and 2, obvious evidence of nodal hilus fat with clear intranodal fat outline (g, h, i)