Correlation of helical and incremental high-resolution thin-section computed tomographic imaging with histomorphometric quantitative evaluation of lungs in dogs

Effects of two alveolar recruitment manoeuvres (sustained inflation and stepwise) followed by positive end-expiratory pressure on cardiac output (measured with lithium dilution), invasive blood pressure and arterial oxygen tension in isoflurane-anaesthetised goats

Alveolar recruitment manoeuvres (ARM) performed during general anaesthesia improve oxygenation; however cardiovascular depression may be observed. The aim of the study was to compare the effects of sustained inflation (SI) and stepwise ARMs on cardiac output (CO), mean arterial blood pressure and arterial oxygen tension (PaO2) in ten mechanically ventilated goats anaesthetised with isoflurane. In the SI ARM, peak inspiratory presure (PIP) was increased to 30 cmH2O and sustained for 20 s. In the stepwise ARM, the PIP was increased by 5 cmH2O each minute for three minutes from 10 to 25 cmH2O. Both ARMs were followed by positive end-expiratory pressure of 5 cmH2O. Paired lithium dilution CO measurements and arterial blood samples were obtained before and after each ARM. The order of the ARM was randomised and each goat was subjected to both techniques. Data was reported as median and interquartile range (IQR). Significance was set at 0.05. The median change in CO (measured by subtracting values after and before ARM) was -0.15 L min-1 (IQR -0.51; 0.03) and - 0.90 L min-1 (IQR -1.69; -0.58) for SI and stepwise ARM respectively (p = 0.04). The median change in PaO2 was 3 kPa (IQR -2.7; 7.6) and 0.4 kPa (IQR -3.4; 5.5) for SI and stepwise ARM respectively (p = 0.03). In conclusion, SI ARM causes less impact on CO and provides a better improvement in PaO2 compared to stepwise ARM in goats.

Imaging and endoscopic diagnosis of lung diseases in small animals. A review

Diagnostic imaging plays a fundamental role in the diagnosis of pulmonary diseases. Radiography, ultrasound, computed tomography, and endoscopy are important tools for achieving a diagnosis. The choice of diagnostic procedure varies according to the patient, the suspected diagnosis and the risk/benefit ratio. Culture, cytology and histology are nearly always necessary to obtain a definitive diagnosis. Several biopsy sampling techniques are described. Surgical biopsies are the gold standard for the diagnosis of bronchiolitis or interstitial lung diseases but often not performed due to the high risk. In humans, the introduction of transbronchial cryobiopsies has led to excellent results in the study of interstitial lung diseases.

Minimal atelectasis and poorly aerated lung on thoracic CT images of normal dogs acquired under sedation

General anesthesia optimizes image quality of thoracic CT in dogs by providing patient immobilization and respiratory control. However, it also comes with disadvantages that may serve as a detractor to the use of CT in veterinary practice. With the use of multidetector helical CT combined with injectable sedation for restraint, parameters such as atelectasis and poorly aerated lung should not be appreciably different from what has been observed in dogs under general anesthesia. This prospective pilot study aimed to evaluate the mean lung attenuation and the amount of atelectasis and poorly aerated lung on thoracic CT images acquired under injectable sedation in normal dogs. The entire thorax of 10 client-owned dogs was scanned. Attenuation measurements were generated by three-dimensional reconstruction software. Mean ± SD lung attenuation was -707.0 ± 60.0. Atelectasis was not identified on any of the scans. Hypoinflated lung, the percentage of lung parenchyma with attenuation greater than -500 and -250 Hounsfield units (HU), was 10.7 ± 4.7% and 2.4 ± 1.2% (mean ± SD), respectively. There was no significant change in these percentages over time. Compared to previously published data, thoracic CT images obtained under sedation had mean attenuation comparable to normal expiratory lung and a lower percentage of poorly aerated lung compared to that of anesthetized dogs. Using sedation to complete canine thoracic CT does not itself lead to alterations of lung attenuation and may confer less hypoinflation and atelectasis than general anesthesia.

Lung ultrasound nodule sign for detection of pulmonary nodule lesions in dogs: Comparison to thoracic radiography using computed tomography as the criterion standard

Thoracic radiography (TR), the most common screening test for pulmonary metastases in dogs, can fail to detect small lesions <3 mm. Lung ultrasonography (LUS) is a widely available imaging modality capable of detecting peripheral nodules but is underutilized for this purpose. Thoracic computed tomography (CT) is the criterion standard for diagnosis of lung metastases and nodular disease but is less practical for a variety of reasons. We hypothesized that LUS would be more sensitive but less specific at detecting nodules consistent with metastatic pulmonary disease in dogs compared to TR, using CT as the criterion standard. This was a masked, single-center prospective study of 62 client-owned dogs evaluated for respiratory signs or pulmonary metastatic neoplasia screening using TR, LUS and CT. Dogs were included if metastatic pulmonary disease was a differential. All imaging modalities were scored as having nodules (yes/no) and other types of pathologic lesions were recorded. Sensitivity (Se), specificity (Sp) and positive (LR+) and negative likelihood ratios (LR-) were determined for TR and LUS. For TR, Se and Sp were 64% and 73%, and LR+ and LR- were 2.37 and 0.49, respectively. For LUS, Se and Sp were 60% and 65% and LR+ and LR- were 1.71 and 0.62, respectively. The results of the study indicate that LUS had a similar Se to TR, with both modalities missing nodules when used for screening. The low Sp and LR- suggests caution should be used when assuming TR and LUS rule out the presence of nodules.

Successful Treatment of Congenital Lobar Emphysema in Multiple Lung Lobes in an English Bulldog Puppy

A 5 mo old male intact English bulldog was evaluated at a veterinary referral hospital for acute respiratory distress and chronic difficulty breathing. Thoracic radiographs revealed multifocal pulmonary hyperinflation and hyperlucency suspected in the left caudal and accessory lung lobes. A thoracic computed tomography scan identified severe diffuse enlargement of the caudal subsegment of the left cranial lung lobe and the dorsal process of the accessory lung lobe, with parenchymal hypoattenuation, rounded margins, and thin pulmonary vessels. Based on clinical signs and imaging findings, he was diagnosed with suspect congenital lobar emphysema in multiple lung lobes. A median sternotomy was performed, which revealed a hyperinflated, emphysematous left cranial lung lobe (caudal subsegment) and accessory lung lobe for which two lung lobectomies were performed. The remaining lung lobes were small and atelectatic. Histopathology revealed bronchial cartilage hypoplasia and aplasia and findings consistent with congenital lobar emphysema. The puppy recovered well from surgical treatment of congenital lobar emphysema, requiring multiple lung lobectomies, with subsequent computed tomography-evidenced re-expansion of the remaining lung lobes 3 mo after surgery. The patient is still alive 1 yr after surgery with a normal activity level and no evidence of respiratory compromise.

Effect of body position and time on quantitative computed tomographic measurements of lung volume and attenuation in healthy anesthetized cats

OBJECTIVE To quantify the effect of time and recumbency on CT measurements of lung volume and attenuation in healthy cats under general anesthesia. ANIMALS 8 healthy research cats. PROCEDURES Anesthetized cats were positioned in sternal recumbency for 20 minutes and then in left, right, and left lateral recumbency (40 minutes/position). Expiratory helical CT scan of the thorax was performed at 0 and 20 minutes in sternal recumbency and at 0, 5, 10, 20, 30, and 40 minutes in each lateral recumbent position. For each lung, CT measurements of lung volume and attenuation and the extent of lung areas that were hyperaerated (-1,000 to -901 Hounsfield units [HU]), normoaerated (-900 to -501 HU), poorly aerated (-500 to -101 HU), or nonaerated (-100 to +100 HU [indicative of atelectasis]) were determined with a semiautomatic threshold-based technique. A restricted maximum likelihood analysis was performed. RESULTS In lateral recumbency, the dependent lung had significantly greater attenuation and a lower volume than the nondependent lung. Within the dependent lung, there was a significantly higher percentage of poorly aerated lung tissue, compared with that in the nondependent lung. These changes were detected immediately after positioning the cats in lateral recumbency and remained static with no further significant time-related change. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that once anesthetized healthy cats were positioned in lateral recumbency, the dependent lung lobes underwent a rapid reduction in lung volume and increase in lung attenuation that did not progress over time, predominantly attributable to an increase in poorly aerated lung tissue.

Computed tomography of the thorax in rabbits: a prospective study in ten clinically healthy New Zealand White rabbits

Background

Literature investigating the normal cross-sectional anatomy of rabbits with computed tomography (CT) is sparse and incomplete. The purpose of the present study was to investigate the normal thoracic structures, in particular the cranial thorax, with CT angiography in 10 clinically healthy New Zealand White (NZW) rabbits.

Results

Absolute and relative measurements of the trachea, heart, thoracic caudal vena cava and aorta, right and left principal bronchi, right and left caudal lobar bronchi and the accompanying branches of the right and left pulmonary artery and vein, right and left lung volume and lung density were taken. The three lobes of the thymus (right ventral, right dorsal and left thoracic lobes) were identified in all rabbits. Both the right dorsal and left thoracic lobes of the thymus extended between the heart and thoracic wall in all individuals with the left lobe reaching more caudally in seven animals. Consequently, the craniocaudal extension of the left lung was smaller than the right lung in these rabbits. Volume of the left lung was significantly smaller than the right (P = 0.005). The cranial mediastinal, right and left tracheobronchial and the aortic thoracic lymph nodes were very small and identified in four, four, seven and ten rabbits, respectively. The heart took up a median of 4.0 intercostal spaces, and in seven rabbits, it was located in the 2nd–5th intercostal space. Median relative cardiac height and width measured 74 and 88%, respectively. The median angle of the trachea to the spine was 5°. Median density between the right and left lung did not significantly differ (− 549 and − 583 Hounsfield units, respectively). In all but one rabbit, atelectasis was present and classified as mild, moderate or severe in six, two and one individuals, respectively. Mild subclinical bronchopneumonia was diagnosed in seven rabbits.

Conclusions

The present study provides species-specific anatomical CT information and reference values for structures in the thorax of the NZW rabbit. Subclinical bronchopneumonia appears to be a common CT finding.

Accuracy of a computed tomography bronchial wall thickness to pulmonary artery diameter ratio for assessing bronchial wall thickening in dogs

Computed tomography is increasingly being used in veterinary medicine to evaluate animals with pulmonary signs such as coughing, tachypnea, and exercise intolerance, however, a quantitative measure of bronchial wall thickening has yet to be validated in veterinary medicine. Canine chronic bronchitis is a disease that is characterized histologically by thickening of the bronchial walls. Thoracic CT images of 16 dogs with chronic bronchitis and 72 dogs presenting for conditions unrelated to cough were evaluated. A ratio comparing the bronchial wall thickness to the adjacent pulmonary artery diameter was obtained in the right and left cranial and caudal lung lobes. There was no significant difference in dogs with chronic bronchitis or unaffected dogs between the left and right hemithorax, patient weight, patient age, image slice thickness, or CT machine used. Dogs with chronic bronchitis were found to have a significantly greater ratio than unaffected dogs (P < 0.001). The ratios in the cranial lung lobes were found to be significantly greater than the caudal lung lobes in both chronic bronchitis and unaffected dogs (P < 0.001). A receiver operating characteristic curve of the ratios in the cranial lung lobes had an area under the curve of 0.912, indicating high accuracy in predicting for bronchial wall thickening. A ratio of ≥ 0.6 in the cranial lung lobes was found to have a sensitivity of 77% and specificity of 100% in predicting for the presence of chronic bronchitis, and we propose using this cut-off as supportive of bronchial wall thickening on CT.

Survey radiography and computerized tomography imaging of the thorax in female dogs with mammary tumors

Background

Accurate early diagnosis of lung metastases is important for establishing therapeutic measures. Therefore, the present study aimed to compare survey thoracic radiographs and computerized tomography (CT) scans to specifically identify lung metastases in female dogs with mammary tumors.

Methods

Twenty-one female dogs, weighing 3 to 34 kg and aged from 5 years to 14 years and 10 months, with mammary tumors were studied. In all dogs before the imaging examinations, fine-needle aspiration cytology of the mammary tumors was performed to confirm the diagnosis. Three-view thoracic radiographs were accomplished: right lateral, left lateral and ventrodorsal views. Sequential transverse images of the thorax were acquired on a spiral Scanner, before and after intravenous bolus injection of nonionic iodine contrast. Soft-tissue and lung windows were applied. All the mammary tumors were surgically removed and examined histologically.

Results

The correlation between the cytological and histological results regarding presence of malignancy was observed in only 17 cases. In radiographic examinations, no dog displayed signs of lung metastases or thorax chest lesions. CT detected lung metastasis in two cases, while small areas of lung atelectasis located peripherally were found in 28.57% of the dogs.

Conclusion

In this study population, spiral CT showed higher sensitivity than chest radiographies to detect lung metastasis; this indicates that CT should be performed on all female dogs with malignant mammary tumors.

Computed tomographic analysis of the effects of two inspired oxygen concentrations on pulmonary aeration in anesthetized and mechanically ventilated dogs

OBJECTIVE

To compare the effect of 2 concentrations of oxygen in inspired gas (fraction of inspired oxygen [FIO(2)] 1.0 or 0.4) on pulmonary aeration and gas exchange in dogs during inhalation anesthesia.

ANIMALS

20 healthy dogs.

PROCEDURES

Following administration of acepromazine and morphine, anesthesia was induced in each dog with thiopental and maintained with isoflurane in 100% oxygen (100% group; n = 10) or a mixture of 40% oxygen and air (40% group; 10). Dogs were placed in dorsal recumbency and were mechanically ventilated. After surgery, spiral computed tomography (CT) of the thorax was performed and PaO(2), PaCO(2), and the alveolar-arterial oxygen tension difference (P([A-a])O(2)) were assessed. The lung CT images were analyzed, and the extent of hyperinflated (-1,000 to -901 Hounsfield units [HUs]), normally aerated (-900 to -501 HUs), poorly aerated (-500 to -101 HUs), or nonaerated (-100 to +100 HUs) areas was determined.

RESULTS

Compared with the 100% oxygen group, the normally aerated lung area was significantly greater and the poorly aerated and nonaerated areas were significantly smaller in the 40% oxygen group. The time to CT (duration of surgery) was similar in both groups. Although PaCO(2) was similar in both groups, PaO(2) and P((A-a))O(2) were significantly higher in the 100% oxygen group. In both groups, pulmonary atelectasis developed preferentially in caudal lung fields.

CONCLUSION AND CLINICAL RELEVANCE

In isoflurane-anesthetized dogs, mechanical ventilation with 40% oxygen appeared to maintain significantly better lung aeration and gas exchange than ventilation with 100% oxygen.

Computed tomography in small animals – Basic principles and state of the art applications

Since its clinical introduction, computed tomography (CT) has revolutionized veterinary medicine and is considered to be one of the most valuable tools for the imaging work-up of neurological, oncological and orthopaedic canine and feline patients. In small animals with acute trauma, particularly those involving complex anatomic areas such as the head, spine or pelvis, CT has been established as a standard imaging method. With the increasing availability of radiation therapy in veterinary medicine, CT has also become the principal tool to stage a tumour, assess response, and guide radiation therapy. The increasing availability of helical CT in veterinary medicine has allowed novel techniques such as spiral CT angiography and high-resolution CT. This review provides a brief overview of the historical and technical development of CT and literature reviews of the major clinical CT applications in small animals such as intracranial and extracranial lesions, the spine, the appendicular skeleton, and abdominal and thoracic diseases.

CHARACTERIZATION OF SEVERE SMALL AIRWAY DISEASE IN A PUPPY USING COMPUTED TOMOGRAPHY

A young Golden Retriever dog developed severe respiratory distress following an initial clinical diagnosis of infectious tracheobronchitis. Severe expiratory flow limitation, associated with exertional respiratory distress and hypoxemia was present. Thoracic images obtained with conventional radiography were characterized by hyperinflation and abnormal bronchial and alveolar patterns. Computed tomography was performed and in conjunction with pulmonary functional changes was diagnostic of small airway disease. The dog was treated with a variety of antibiotics, anti-inflammatory agents, and antitussives, but the clinical signs worsened and the puppy was euthanized. Pathologic examination confirmed severe small airway disease, with emphysema and bronchiolitis.

IMAGING DIAGNOSIS: ACUTE LUNG INJURY FOLLOWING MASSIVE BEE ENVENOMATION IN A DOG

A 5-year-old neutered male mixed breed dog presented for increased respiratory effort after being stung by over 100 bees and developing anaphylactic shock. Given the history, clinical signs and thoracic radiographic findings of a mild bilateral interstitial pattern, acute lung injury/acute respiratory distress syndrome (ALI/ARDS) was suspected. Further testing was performed to support this diagnosis. On computed tomographic images, there was a diffuse bilateral opacification of the lungs, with preservation of bronchial and vascular margins. Pulmonary function testing indicated decreased pulmonary compliance, decreased diffusion capacity and decreased functional residual capacity. These results supported the diagnosis of ALI/ARDS secondary to bee sting envenomation and development of anaphylactic shock. After 8 days of treatment with oxygen, steroids, antibiotics, and bronchodilators the dog improved. This case demonstrates the usefulness of computed tomography and pulmonary function testing in the diagnosis of ALI/ARDS.

Computed tomography and cross-sectional anatomy of the thorax in clinically normal dogs

OBJECTIVE

To provide a detailed anatomic description of the thorax in clinically normal dogs by means of computed tomography.

ANIMALS

4 clinically normal adult German Shepherd Dogs weighing 28 to 37 kg.

PROCEDURE

Dogs were anesthetized and positioned in ventral recumbency for computed tomographic (CT) examination of the thorax. A CT image from the thoracic inlet to the diaphragm was made by use of a third-generation scanner with a slice thickness of 5 mm. Individual images were reviewed by use of soft tissue (window width, 250 Hounsfield units; window level, 35 Hounsfield units) and lung (window width, 1,000 Hounsfield units; window level, -690 Hounsfield units) settings. One dog, weighing 28 kg, was euthanatized, bound on a wooden frame in the same position as used for CT examination, and frozen at -14 degrees C until solid. By use of an electric band saw, the frozen thorax was sectioned at 10-mm-thick intervals. Slab sections were immediately cleaned, photographed, and compared with corresponding CT images.

RESULTS

Anatomic sections were studied, and identified anatomic structures were matched with structures on corresponding CT images. Except for some blood vessels and details of the heart, most of the bony and soft tissue structures of the thorax discerned on anatomic slices could be found on matched CT images.

CONCLUSIONS AND CLINICAL RELEVANCE

Because CT images provide detailed information on most structures of the canine thorax, results of our study could be used as a guide for evaluation of CT images of the thorax of dogs with thoracic diseases.

Correlation of helical and incremental high-resolution thin-section computed tomographic and histomorphometric quantitative evaluation of an acute inflammatory response of lungs in dogs

OBJECTIVE

To compare quantitative densitometric computed tomography (CT), morphometric, and histologic data of normal lungs in dogs with similar parameters obtained after induction of an acute inflammatory response and determine whether CT densitometry correlated with histopathologic changes.

ANIMALS

6 healthy adult dogs.

PROCEDURE

After initial CT, 1 mL of 0.1 M hydrochloric acid (HCI) and 3 mL of autologous blood were instilled into the right middle (RM) and caudal segment of the left cranial (LCCd) lung lobes, respectively. Immediately and 24 hours after instillation, CT was repeated. At 24 hours, dogs were euthanatized and lungs were fixed and sampled for morphometric and histologic evaluation. The CT data were compared with lung morphology and morphometry by use of unpaired t tests. Comparison with lungs from control dogs was performed using Spearman rank correlation coefficients.

RESULT

Mean Hounsfield units (HU) from control and baseline HU from experimental dogs were identical. Immediately after instillation of HCI or blood, there was increased attenuation in both lobes. Autologous blood initially induced severe changes that almost completely resolved at 24 hours; HCI induced severe changes at 24 hours. Significant increases in percentage of parenchymal airspace and alveolar diameter resulted in decreased surface area-to-volume ratio in lobes receiving HCl. Histologic scores were significantly higher in the RM lobe, compared with controls.

CONCLUSIONS AND CLINICAL RELEVANCE

Computed tomography attenuation correlated well with histomorphometry and histologic findings in this model. Lung lesions after autologous blood were transient and of limited severity. Lesions induced by HCl were severe; alterations in morphometric and histologic parameters were reflected in CT attenuation measurements.