14: Extrathoracic Structures


CHAPTER 14
Extrathoracic Structures


Clifford R. Berry1 and Federico R. Vilaplana Grosso2


1 Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA


2 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA


Overview


The first area to be evaluated using the thoracic interpretation paradigm is the extrathoracic structures. These include the soft tissue and osseous structures of the thoracic limbs, cervical and thoracic spine, sternum and ribs, diaphragm, the organs of the cranial abdomen and the peritoneal space. This chapter reviews the normal radiographic appearance and abnormalities associated with each extrathoracic structure.


Thoracic Limbs


Depending on the size of the dog, there will be a variable amount of the thoracic limb present on the radiographic images. In smaller dogs and cats, the proximal antebrachium through the scapula will be seen and are superimposed over each other on lateral projections. In larger dogs, the scapula and glenohumeral joint may be the only portion of the thoracic limb visualized. Common abnormalities associated with the thoracic limbs include traumatic injury and degenerative joint disease of the glenohumeral or elbow joints. The degenerative change is seen as osteophyte formation of the periarticular structures. For the glenohumeral joint, this would include the caudal aspect of the glenoid cavity and the caudal aspect of the humeral head (Figure 14.1). Other common abnormalities would be fractures related to trauma (Figure 14.2).

Photos depict (A) five-year-old Labrador with an incidental finding of a focal subchondral defect in the caudal humeral head (white arrow). (B) Ten-year-old German shepherd with degenerative periarticular osteophytes of the caudal glenoid cavity and humeral head (white arrows).

FIGURE 14.1 (A) Five‐year‐old Labrador with an incidental finding of a focal subchondral defect in the caudal humeral head (white arrow). (B) Ten‐year‐old German shepherd with degenerative periarticular osteophytes of the caudal glenoid cavity and humeral head (white arrows).

Photos depict six-year-old mixed-breed dog with acute trauma (hit by car).

FIGURE 14.2 Six‐year‐old mixed‐breed dog with acute trauma (hit by car). On the VD (A) and right lateral (B) images there is a comminuted scapular fracture with the spine of the scapula being displaced and angled. (C) A 15‐month‐old Labrador with acute trauma. The right lateral thoracic image is shown and there is ventral displacement (luxation) of the caudal thoracic spine at T11–12 with a caudal ventral endplate fracture of T11 (white arrow). Also notice the pulmonary vessels and the cardiac silhouette are small, consistent with hypovolemia.


Aggressive changes of the osseous structures of the thoracic limb should not be missed. Primary bone tumors are commonly seen in the proximal humeral metaphysis and can have aggressive areas of osteolysis and osteoproliferation (Figure 14.3). Primary tumors of the scapula are less common but should not be missed when evaluating the scapula on lateral images even though they are superimposed. Confirmation of laterality can be done using the ventrodorsal (VD) or dorsoventral (DV) radiograph (Figure 14.4). Palisading periosteal reaction along the diaphyseal cortices of the humeri can be seen in dogs with hypertrophic osteopathy (see Chapter 10).

Photo depicts nine-year-old German shepherd with a proximal right humeral aggressive lesion.

FIGURE 14.3 Nine‐year‐old German shepherd with a proximal right humeral aggressive lesion. There is marked osteolysis and irregular periosteal reaction involving the proximal humeral diaphysis, metaphysis, and epiphysis consistent with a primary bone tumor. In addition, there are multiple pulmonary soft tissue nodules (variably sized) along with a pneumothorax as evidenced by dorsal elevation of the ventral lung lobes and the cardiac silhouette on this right lateral image. There are thickened pleural margins noted ventrally as evidenced by the irregular soft tissue opaque lines. Ventral spondylosis deformans is also noted in the cranial to midthoracic spine.

Photos depict ten-year-old Labrador with an aggressive lesion in the caudal body of the left scapula (ill-defined lysis).

FIGURE 14.4 Ten‐year‐old Labrador with an aggressive lesion in the caudal body of the left scapula (ill‐defined lysis). There are multiple areas of osseous expansion and extrapleural signs involving the ribs (A,B, with close‐ups in C,D). In addition, there is a compression, pathologic fracture of the fourth sternebrae. These changes were all secondary to a primary osteosarcoma of the left scapula with metastatic disease to other osseous structures including the ribs and sternum. In (E) and (F), there is a right‐sided pulmonary mass in this 12‐year‐old MN Havenese. This was a primary lung tumor. In addition, there is extreme periosteal reaction that is smooth along all the bones included in the images. These reactions are consistent with hypertrophic osteopathy.


Thoracic Wall, Vertebral Column, Ribs, and Sternum


A radiolucent space is noted between all thoracic vertebrae and all sternebrae except between S7 and the xiphoid process. This radiolucency represents the intervertebral disc and intersternebral cartilage, respectively. In the thoracic vertebral location, the intervertebral disc is made up of an outer annulus fibrosis and an inner nucleus pulposus, being a fibrocartilaginous joint. A cartilaginous center is noted to the synchondrosis joint of the sternebral discs. Degenerative changes of the intervertebral disc and intersternebral spaces are the most common changes seen involving the vertebrae and the sternum. These changes include intervertebral disc/intersternebral space narrowing, adjacent endplate sclerosis and ventral spondylosis deformans (intervertebral disc space) or ventral/dorsal osseous proliferation (sternal cartilaginous degenerative change). These areas of osteoproliferation are smoothly marginated, are located at the edge of the vertebral body and sternal segment, and do not appear aggressive (Figure 14.5).

Photos depict ten-year-old MN boxer with multifocal areas of degenerative change.

FIGURE 14.5 Ten‐year‐old MN boxer with multifocal areas of degenerative change. These include glenohumeral, elbow, costochondral, intersternebral, sternocostal, and intervertebral disc degenerative changes. These changes are seen on both the right (A) and left lateral (B) images and primarily consist of osteoproliferative changes without aggressive areas of lysis or osseous destruction. Notice there is a small amount of gas present within the cranial thoracic esophagus on the left lateral image (B; white arrow). This results in a “tracheoesophageal stripe sign” (combination of the dorsal wall of the trachea and the ventral wall of the esophagus that border efface with each other). On the right lateral image, there is a focal linear area of plate‐like atelectasis (white arrow) superimposed over the trachea, that represents atelectasis along subpleural margins of the right and/or left cranial lung lobes.


The vertebral bodies of the thoracic spine articulate with the ribs on both the right and left sides. The ribs are uniform in mineral opacity and articulate ventrally with the costal cartilage at the costochondral junction (Figure 14.6). The costal cartilage will mineralize early on in the animal’s life so that a uniform mineral opaque structure is present that articulates with the sternum or with other costal cartilages caudally. The costochondral junctions can undergo enlargement and degenerative changes, creating an extrapleural sign (Box 14.1, Figure 14.7). Bassett hounds routinely have an extrapleural sign on lateral, ventrodorsal or dorsoventral radiographs (Figure 14.8).

Photos depict right lateral images from various dogs (A–C) and a cat (D).

FIGURE 14.6 Right lateral images from various dogs (A–C) and a cat (D). (A) Seven‐year‐old dog with congenital malformation of the sternum including elongation of the manubrium, fusion of the second, third, fourth, and fifth sternebral segments. These are considered incidental findings. (B) Two‐year‐old dog with mineralization of the costal cartilages and normal sternebral development. Note the lack of complete mineralization of the first set of costal cartilages that can be a common finding in younger dogs and cats. (C) Similar changes seen in a different dog that was 3 years old. (D) Normal sternal and costal cartilage appearance in an 11‐year‐old cat.

Photo depicts right lateral radiograph from a 9-year-old bassett hound.

FIGURE 14.7 Right lateral radiograph from a 9‐year‐old bassett hound. Note the costochondral degenerative changes with irregular mineralization and indentation of the pleural space such that an extrapleural sign is noted along the ventral caudal thorax (white arrows). Degenerative ventral spondylosis deformans is noted in the cranial thoracic vertebrae.

Photo depicts ventrodorsal radiograph from an 8-year-old bassett hound.

FIGURE 14.8 Ventrodorsal radiograph from an 8‐year‐old bassett hound. There is increased soft tissue opacity noted along the lateral margins of the thorax because of the indentation from the costochondral junctions (white arrows). Benign soft tissue mineralization is noted lateral to the right seventh intercostal space.


Aggressive lesions of the vertebral bodies, disc spaces, ribs, and sternum are characterized by osteolysis and cortical disruption. Vertebral body tumors can be lytic and result in vertebral body collapse and a compression fracture (Figure 14.9). Discospondylitis is an infection of the intervertebral disc space. The radiographic features of discospondylitis include intervertebral disc space narrowing/collapse, endplate lysis of the caudal and cranial aspects of the vertebral bodies at the intervertebral disc space, and osseous proliferation associated with the vertebral bodies in an attempt to wall off the infectious agent (Figure 14.10) [1]. Infections of the intersternebral disc spaces have similar radiographic abnormalities. Nocardia and Actinomyces sp. infections have been described involving the sternum, vertebrae, pleural space, and the different lung lobes, particularly the accessory lung lobe (Figure 14.11). Primary tumors or secondary soft tissue tumors with sternebral involvement also occur (Figure 14.12).

Photos depict right lateral thoracic (A) and close-up (B) radiographs from a 7-year-old German shepherd with a compression fracture of T2 (white arrow).

FIGURE 14.9 Right lateral thoracic (A) and close‐up (B) radiographs from a 7‐year‐old German shepherd with a compression fracture of T2 (white arrow). This was secondary to a primary bone tumor. In (A) there is a decrease in size of the pulmonary vasculature and cardiac silhouette consistent with hypovolemia. (C) Compression fracture luxation of T2 with dorsal displacement of the caudal thoracic vertebral column relative to T2 (white arrow). There is osteolysis of T2 with lysis of the lamina and spinous process. This was secondary to a primary bone tumor (osteosarcoma). There is a decrease in pulmonary vascular and cardiac silhouette size consistent with hypovolemia.

Photos depict (A) right lateral radiograph from a 7-year-old German shepherd with several areas of discospondylitis. (B,C) Sagittal reconstructions from CT studies from two different dogs with discospondylitis. (D) There is lysis of the endplates noted between the third and fourth sternal segments with surrounding osteosclerosis and ill-defined periosteal reaction. This was secondary to Aspergillus sp. infection.

FIGURE 14.10 (A) Right lateral radiograph from a 7‐year‐old German shepherd with several areas of discospondylitis. There is lysis and osteoproliferation associated with the endplates of T4–5 and T5–6. Collapse of the intervertebral disc spaces is present. (B,C) Sagittal reconstructions from CT studies from two different dogs with discospondylitis. In (B) there is collapse of the T12–13 intervertebral disc space with endplate lysis and ventral periosteal proliferation that is irregular extending from the endplate to the midbody of each vertebra. In (C) there is collapse of the T9–10 intervertebral disc space, endplate lysis and subluxation of T10 relative to T9 with angulation being noted at the site. There is some sclerosis noted within the T9 and T10 vertebral bodies. (D) There is lysis of the endplates noted between the third and fourth sternal segments with surrounding osteosclerosis and ill‐defined periosteal reaction. This was secondary to Aspergillus sp. infection.

Photos depict actinomyces infection with accessory lung lobe mass, pleural effusion with gas (abscess on the left lateral) and smooth periosteal reaction noted along the dorsal aspect of the seventh sternebrae ((A) – right lateral, (B) – left lateral with white arrow over S7).

FIGURE 14.11 Actinomyces infection with accessory lung lobe mass, pleural effusion with gas (abscess on the left lateral) and smooth periosteal reaction noted along the dorsal aspect of the seventh sternebrae ((A) – right lateral, (B) – left lateral with white arrow over S7). (C) Left lateral radiograph from a dog with intersternebral infections at S3–4 and S4–5. Endplate lysis, irregularity, and sclerosis are present. There is mild soft tissue thickening noted dorsal to these areas along the ventral pleural margins. A focal accumulation of gas is present, resulting in a tracheal esophageal stripe sign (white arrow; soft tissue linear shadow of the dorsal wall of the trachea and ventral wall of the esophagus that are border effaced due to both being soft tissue opacity).

Photos depict multiple lateral thoracic radiographic examples of neoplastic and infectious processes involving the sternum.

FIGURE 14.12 Multiple lateral thoracic radiographic examples of neoplastic and infectious processes involving the sternum. (A) Focal soft tissue mass with osteolysis and proliferation of the third sternebrae. Changes involving the fourth sternebrae are also noted. There is focal soft tissue opacity along the floor of the thoracic cavity/pleural space at the sternal abnormalities. These were secondary to a fibrosarcoma with invasion of the sternebrae and thorax. (B) There is lysis and collapse of the third sternebral segment. A focal soft tissue mass is noted extending into the ventral thorax. These changes were secondary to an osteosarcoma of the third sternebral segment. (C) A focal osteoproliferative lesion of the fifth sternebral segment with an associated ventral pleural mass and pleural effusion. (D) There is a focal soft tissue mass effect with involvement of the fourth and fifth sternebral segments. There is osteolysis and osteoproliferation of these sternebrae and ill‐defined periosteal reaction surrounding the sternal segments that are involved. This tumor was a histiocytic sarcoma.


Common rib abnormalities include fractures and tumors. Acute rib fractures can be seen as breaks in the cortices of the rib with displacement of one margin of the fracture relative to the other (Figure 14.13). Chronic rib fractures are characterized by varying degrees of callus formation and healing (Figure 14.13). Chronic rib fractures can also be seen in dogs and cats with thoracic bellows secondary to chronic pulmonary or pleural space abnormalities (Figure 14.14).

Photo depicts ventrodorsal image from a dog with generalized osteopenia secondary to chronic Cushing disease.

FIGURE 14.13 Ventrodorsal image from a dog with generalized osteopenia secondary to chronic Cushing disease. There are multiple rib fractures that are acute (sharply marginated without periosteal reaction) and chronic fractures (ill‐defined margins, callus formation) and extrapleural signs noted on both the left and right sides.

Photos depict thoracic bellows with chronic rib fractures resulting from a chronic pleural effusion (chylothorax) with a restrictive pleuritis and thickening of the visceral pleura, particularly surrounding the left caudal lung lobe.

FIGURE 14.14 Thoracic bellows with chronic rib fractures resulting from a chronic pleural effusion (chylothorax) with a restrictive pleuritis and thickening of the visceral pleura, particularly surrounding the left caudal lung lobe. The lung lobe is restricted by the pleural thickening so that it will not reinflate when the air is withdrawn from the pleural space (pneumothorax). Several gas opacities are noted adjacent to the left side of the thorax consistent with prior thoracocentesis.


Rib tumors can occur anywhere along the osseous portion of the rib and the most common rib tumor is an osteosarcoma. Radiographic features of rib tumors are summarized in Box 14.2. The lesion is aggressive with an expansile appearance that results in cortical lysis (Figures 14.15 and 14.16). Varying degrees of osseous proliferation may be present with an aggressive amorphous appearance. A pleural effusion may or may not be present (Figure 14.17). Metastasis of the primary rib tumor to the lungs can occur. Secondary or metastatic neoplasia of the vertebrae and ribs is common in adenocarcinomas that have osseous metastatic changes (Figure 14.18). A differential for this pattern of metastasis is multiple myeloma (Figure 14.19).

Photos depict right lateral (A) and ventrodorsal (B) thoracic radiographs.

FIGURE 14.15 Right lateral (A) and ventrodorsal (B) thoracic radiographs. Focal osteosclerotic lesion associated with the dorsal body of the right 10th rib from an 11‐year‐old DSH (white arrows). There is smooth periosteal proliferation surrounding the central mineral opaque structures associated with the rib. This was resected and determined to be an osteosarcoma in this cat. There is no radiographic evidence of pulmonary metastatic disease.

Photos depict right lateral (A) and ventrodorsal (B) thoracic radiographs from an 8-year-old dog with a left thoracic wall mass.

FIGURE 14.16 Right lateral (A) and ventrodorsal (B) thoracic radiographs from an 8‐year‐old dog with a left thoracic wall mass. There is complete lysis associated with the left fifth rib centrally with a mass effect extending into the left pleural space. A lobulated soft tissue mass was also present within the caudal segment of the left cranial lung lobe and the ventral segment of the left caudal lobe. The rib mass was determined to be an osteosarcoma with multiple pulmonary metastatic lesions.

Photos depict right lateral (A), left lateral (B), and ventrodorsal (C) thoracic radiographs from a dog with a right-sided pleural effusion (retractions of the lung lobes, multiple pleural fissure lines, soft tissue opacity border effacing the cardiac silhouette and the diaphragm).

FIGURE 14.17 Right lateral (A), left lateral (B), and ventrodorsal (C) thoracic radiographs from a dog with a right‐sided pleural effusion (retractions of the lung lobes, multiple pleural fissure lines, soft tissue opacity border effacing the cardiac silhouette and the diaphragm). There is an irregular ill‐defined area of osteoproliferation associated with the right eighth rib with areas of lysis at the level of the described changes. The rib mass was resected and was an osteosarcoma on histology.

Photo depicts ventrodorsal thoracic radiograph from a 10-year-old terrier that presented for a transitional cell (urothelial) carcinoma.

FIGURE 14.18 Ventrodorsal thoracic radiograph from a 10‐year‐old terrier that presented for a transitional cell (urothelial) carcinoma. There is a focal expansile, osteolytic lesion of the left sixth rib with an extrapleural sign. An ultrasound‐guided aspirate of this lesion was determined to be carcinoma on cytology, presumed to be metastatic from the known urogenital neoplasm.

Photos depict right lateral (A), ventrodorsal (B), and close-up ventrodorsal (C) thoracic radiographs from a 5-year-old Shetland sheepdog.

FIGURE 14.19 Right lateral (A), ventrodorsal (B), and close‐up ventrodorsal (C) thoracic radiographs from a 5‐year‐old Shetland sheepdog. There are multiple osteolytic lesions of the thoracic spine, sternum, and ribs. On the close‐up, ventrodorsal image there are numerous expansile, osteolytic lesions associated with the left ribs. An extrapleural sign is present involving the left third rib secondary to an expansile lesion. These changes were confirmed to be multiple myeloma.

Apr 2, 2023 | Posted by in ANIMAL RADIOLOGY | Comments Off on 14: Extrathoracic Structures

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