# Ultrasonography in Avian Patients

## Quick Answer

- Ultrasonography in avian patients requires high-frequency transducers, typically 10 to 18 MHz, to resolve the small coelomic structures of birds, and patient positioning must account for the air sac system that blocks sound wave transmission.
- The normal avian coelomic ultrasound examination follows a systematic cranial-to-caudal sweep that identifies the liver, gastrointestinal tract, kidneys, and reproductive organs, with the proventriculus and ventriculus recognized by their distinct wall layers.
- Interpretation is limited by the acoustic shadowing created by air-filled lungs and air sacs, the small size of avian organs, and the need for species-specific reference values, such as the mean jejunal wall thickness of 2.1 mm reported in healthy chickens.

## Indications for Avian Ultrasonography

Ultrasonography serves as a primary diagnostic imaging tool in avian medicine when radiographic findings are inconclusive or when soft tissue detail is required. The modality provides real-time evaluation of coelomic organs without ionizing radiation, which matters for serial monitoring of chronic conditions. Birds present unique challenges because their respiratory system includes air sacs that extend throughout the coelomic cavity, creating acoustic interfaces that reflect sound waves and obscure deeper structures.

Common indications for avian ultrasound include weight loss with unknown cause, palpable coelomic mass, suspected reproductive disease in female birds, gastrointestinal signs such as regurgitation or changes in droppings, and monitoring of confirmed conditions like hepatomegaly or renomegaly. The American Veterinary Medical Association emphasizes the importance of regular veterinary examinations for pet birds, and ultrasound often forms part of the diagnostic workup when physical examination findings suggest internal disease [1].

The avian patient requires a different approach than mammals because the air sac system limits acoustic windows. The liver, gastrointestinal tract, and reproductive organs are the primary targets of examination. The heart can be evaluated through a specialized window, but echocardiography in birds demands advanced training and equipment. The kidneys are located within the synsacrum and are partially obscured by the air sacs, making complete evaluation difficult.

Ultrasound is particularly valuable for guiding aspiration or biopsy procedures in birds. The real-time nature of the examination allows the clinician to visualize the needle tip as it enters the target organ, reducing the risk of hemorrhage or inadvertent puncture of adjacent structures. This application requires careful patient stabilization and often benefits from sedation or anesthesia to minimize movement.

The decision to perform ultrasound instead of computed tomography or endoscopy depends on the suspected disease process, the stability of the patient, and the equipment available. Ultrasound provides excellent soft tissue detail for the liver, spleen, and reproductive tract. Computed tomography provides superior bone detail and is not limited by air interfaces, but it requires general anesthesia and specialized equipment that may not be available in general practice [4].

## Avian Anatomy Relevant to Ultrasound

The avian coelomic cavity differs substantially from the mammalian abdominal cavity. Birds lack a diaphragm, and the coelomic cavity extends from the thoracic inlet to the vent. The air sac system, consisting of the cervical, clavicular, cranial thoracic, caudal thoracic, and abdominal air sacs, occupies significant portions of the cavity. These air-filled structures reflect ultrasound waves completely, creating shadowing artifacts that obscure organs positioned behind them.

The liver is the largest organ in the avian coelomic cavity and is positioned cranially and ventrally. It consists of two lobes that surround the heart and proventriculus. The right lobe is typically larger than the left lobe in most species. The liver is the primary acoustic window for examining the coelomic cavity because it transmits sound waves well and displaces the air sacs ventrally.

The gastrointestinal tract includes the proventriculus, ventriculus, small intestine, and large intestine. The proventriculus is a glandular stomach located cranial to the ventriculus. The ventriculus, also called the gizzard, is a muscular organ with thick walls that varies in size depending on the species and diet. Granivorous birds have large, muscular ventriculi, while carnivorous birds have smaller, thinner-walled ventriculi.

The reproductive tract differs between males and females. Female birds typically have only a left ovary and oviduct, although some species retain a vestigial right ovary. The ovary is located cranial to the kidney and caudal to the lung. The oviduct extends from the ovary to the cloaca and consists of the infundibulum, magnum, isthmus, shell gland, and vagina. Male birds have paired testes located cranial to the kidneys.

The kidneys are located in the renal fossae of the synsacrum, which is the fused caudal vertebrae. Each kidney has three divisions: cranial, middle, and caudal. The kidneys are partially covered by the abdominal air sacs, which limits ultrasound evaluation of their dorsal aspects. The ureters extend from the kidneys to the urodaeum of the cloaca.

The spleen is a small, rounded organ located on the right side of the coelomic cavity, adjacent to the proventriculus and the right liver lobe. It is often difficult to identify in normal birds because of its small size and variable position. The pancreas is located within the duodenal loop and is also difficult to identify ultrasonographically in normal birds.

## Transducer Selection and Equipment

Transducer selection is the most critical equipment decision in avian ultrasonography. The small size of avian organs and the superficial location of most target structures require high-frequency transducers to achieve adequate resolution. Linear array transducers with frequencies between 10 and 18 MHz provide the best image quality for most avian applications. These transducers produce a rectangular image with excellent near-field resolution, which is ideal for examining superficial structures.

Microconvex transducers with frequencies between 8 and 12 MHz are useful for examining deeper structures and for imaging through small acoustic windows. The curved array produces a sector-shaped image that allows the operator to image through the intercostal spaces or the ventral midline. These transducers are particularly useful for cardiac evaluation and for imaging the cranial coelomic cavity.

The choice between linear and microconvex transducers depends on the target organ and the size of the patient. Linear transducers provide superior resolution for superficial structures such as the liver, gastrointestinal tract, and reproductive organs in small birds. Microconvex transducers are preferred for larger birds and for structures that require a wider field of view, such as the kidneys or the heart.

Ultrasound biomicroscopy represents a specialized application of high-frequency ultrasound that uses frequencies above 30 MHz to image microscopic structures. A study of ophthalmologically normal pigeons demonstrated that ultrasound biomicroscopy could be used to evaluate the anterior ocular segment, providing measurements of the ciliary cleft and iridocorneal angle [7]. This technique requires specialized equipment that is not commonly available in general veterinary practice, but it demonstrates the potential of high-frequency ultrasound for detailed avian imaging.

The ultrasound machine settings must be adjusted for avian patients. The depth should be set to the minimum that allows visualization of the target structure, typically 2 to 5 cm for small birds. The gain should be adjusted to produce a uniform image without excessive brightness or shadowing. The focus should be set at the level of the target structure to optimize lateral resolution.

Coupling gel is applied to the transducer and the patient's skin. Feathers must be parted or removed to allow direct contact between the transducer and the skin. Alcohol can be used to wet the feathers and improve contact, but it evaporates quickly and may cause hypothermia in small patients. Warm coupling gel is preferred to minimize heat loss.

## Patient Preparation and Positioning

Patient preparation is essential for successful avian ultrasonography. Feathers are the primary obstacle to sound wave transmission because they trap air and create acoustic shadowing. The feathers over the ventral coelomic region must be parted or plucked to expose the skin. Plucking is preferred for repeated examinations because it provides a consistent acoustic window, but it removes insulation and increases heat loss.

The ventral approach is the standard positioning for avian coelomic ultrasound. The bird is placed in dorsal recumbency with the wings gently extended and the legs positioned caudally. This position provides access to the ventral midline, which is the primary acoustic window for the liver, gastrointestinal tract, and reproductive organs. The bird must be restrained securely to prevent movement during the examination.

The bird should be positioned on a warm surface to minimize heat loss during the examination. A circulating warm water blanket or a heated examination table is recommended. The ambient temperature of the examination room should be increased to compensate for the loss of feather insulation. Hypothermia is a significant risk in small birds, and the examination should be completed as quickly as possible.

Sedation or anesthesia may be required for uncooperative patients or for prolonged examinations. The choice of sedation protocol depends on the species, the patient's condition, and the anticipated duration of the examination. Light sedation is often sufficient for ultrasound because the procedure is noninvasive and does not cause significant pain. General anesthesia may be required for birds that are fractious or for procedures such as ultrasound-guided biopsy.

The examination should be performed in a quiet, dimly lit room to minimize stress to the patient. The ultrasound machine should be positioned so that the operator can view the screen while maintaining control of the transducer. A second person may be needed to restrain the bird and monitor its condition during the examination.

The ventral approach provides access to the liver, which serves as the primary acoustic window for the coelomic cavity. The transducer is placed on the ventral midline, just caudal to the keel bone, and angled cranially to image the liver and heart. The transducer is then moved caudally to image the gastrointestinal tract, reproductive organs, and kidneys.

## Normal Sonographic Appearance of Avian Organs

### Liver

The liver appears as a homogeneous, moderately echogenic structure with a smooth contour. The hepatic parenchyma has a uniform echotexture that is similar to or slightly more echogenic than the spleen. The hepatic vessels appear as anechoic tubular structures within the parenchyma. The gallbladder, when present, appears as an anechoic, fluid-filled structure with a thin wall.

The liver is the primary acoustic window for the coelomic cavity because it transmits sound waves well and displaces the air sacs ventrally. The right liver lobe is typically larger than the left lobe and extends further caudally. The liver surrounds the heart cranially and the proventriculus and ventriculus caudally.

Hepatomegaly is a common finding in avian patients and can be detected by assessing the liver size relative to the coelomic cavity. The liver should not extend beyond the caudal border of the sternum in normal birds. The liver margins should be sharp and well-defined. Rounding of the liver margins or extension beyond the sternum suggests hepatomegaly.

The hepatic parenchyma should be evaluated for focal or diffuse changes in echogenicity. Diffuse hyperechogenicity may indicate fatty infiltration or fibrosis. Focal hypoechoic or hyperechoic lesions may indicate abscesses, neoplasia, or granulomas. The presence of free fluid around the liver suggests coelomic effusion.

### Gastrointestinal Tract

The proventriculus appears as a tubular structure with a thin, moderately echogenic wall and a lumen that may contain ingesta or fluid. The proventricular wall consists of multiple layers that can be distinguished with high-frequency transducers. The mucosal layer appears as a thin, hyperechoic line, while the muscular layer appears as a thicker, hypoechoic band.

The ventriculus appears as a rounded or oval structure with a thick, muscular wall. The ventricular wall is typically more echogenic than the proventricular wall because of the dense muscular layer. The lumen of the ventriculus contains ingesta and grit, which appear as hyperechoic material with acoustic shadowing. The ventriculus is located caudal and slightly to the left of the proventriculus.

The small intestine appears as multiple tubular structures with a characteristic layered appearance. The intestinal wall consists of five layers that can be distinguished with high-frequency transducers: the mucosal surface, mucosa, submucosa, muscularis, and serosa. The normal intestinal wall thickness varies by species and location within the intestinal tract.

A study of 89 clinically normal chickens found that the mean jejunal wall thickness was 2.1 mm, with a standard error of 0.08 mm [11]. The study found no statistically significant correlation between body weight and jejunal wall thickness in the chickens examined [11]. This finding suggests that body weight should not be used to predict normal intestinal wall thickness in chickens, and species-specific reference values are needed for accurate interpretation.

The intestinal lumen may contain fluid, gas, or ingesta. Gas within the intestinal lumen appears as hyperechoic foci with distal shadowing or reverberation artifacts. Fluid within the intestinal lumen appears as anechoic material. The intestinal wall should be evaluated for thickening, loss of the normal layered appearance, or the presence of masses.

### Reproductive Organs

The ovary in female birds appears as a cluster of small, rounded follicles of varying sizes. The follicles appear as anechoic to hypoechoic structures with thin, echogenic walls. The size and number of follicles vary with the reproductive status of the bird. Active follicles are larger and more numerous than inactive follicles.

The oviduct appears as a tubular structure with a thick, layered wall. The oviduct is not always visible in nonlaying birds because it is small and collapsed. In laying birds, the oviduct is enlarged and contains eggs at various stages of development. An egg within the oviduct appears as a large, rounded structure with a hyperechoic shell and anechoic contents.

The testes in male birds appear as oval, homogeneous structures located cranial to the kidneys. The testes have a moderately echogenic parenchyma with a smooth contour. The size of the testes varies with the reproductive status of the bird. Active testes are larger and more echogenic than inactive testes.

Reproductive disease is a common indication for avian ultrasound. Egg binding, egg peritonitis, and reproductive neoplasia can be detected with ultrasound. Egg binding appears as an egg within the oviduct that is not progressing normally. Egg peritonitis appears as free fluid and echogenic material within the coelomic cavity. Reproductive neoplasia appears as masses within the ovary, oviduct, or testes.

### Kidneys

The kidneys are located in the renal fossae of the synsacrum and are partially obscured by the abdominal air sacs. The cranial division of the kidney is the most accessible for ultrasound examination. The kidneys appear as moderately echogenic structures with a smooth contour and a homogeneous echotexture.

The renal parenchyma is typically more echogenic than the liver and less echogenic than the spleen. The renal vessels and ureters may be visible as anechoic tubular structures within the parenchyma. The kidneys are difficult to evaluate completely because of the overlying air sacs, which create acoustic shadowing.

Renomegaly can be detected by assessing the kidney size relative to the synsacrum. The kidneys should not extend beyond the borders of the synsacrum in normal birds. The renal parenchyma should be evaluated for focal or diffuse changes in echogenicity. The presence of hydronephrosis or renal calculi can be detected with ultrasound.

### Spleen

The spleen is a small, rounded organ located on the right side of the coelomic cavity, adjacent to the proventriculus and the right liver lobe. The spleen appears as a homogeneous, moderately echogenic structure with a smooth contour. The spleen is often difficult to identify in normal birds because of its small size and variable position.

Splenomegaly can be detected by assessing the spleen size relative to the coelomic cavity. The spleen should not exceed the size of the proventriculus in normal birds. The splenic parenchyma should be evaluated for focal or diffuse changes in echogenicity. The presence of nodules or masses within the spleen suggests neoplasia or granulomatous disease.

## Ultrasound-Guided Procedures

Ultrasound-guided aspiration and biopsy are valuable diagnostic procedures in avian medicine. These procedures allow the clinician to obtain samples from coelomic organs with minimal trauma and reduced risk of complications. The real-time nature of ultrasound allows the clinician to visualize the needle tip as it enters the target organ, reducing the risk of inadvertent puncture of adjacent structures.

Ultrasound-guided fine-needle aspiration is used to obtain samples for cytologic evaluation. A small-gauge needle, typically 22 to 25 gauge, is advanced through the skin and body wall into the target organ under ultrasound guidance. The needle is moved back and forth within the organ to dislodge cells, and suction is applied to aspirate the sample. The sample is then expelled onto a slide for cytologic evaluation.

Ultrasound-guided biopsy is used to obtain larger samples for histopathologic evaluation. A biopsy needle, typically 18 to 20 gauge, is advanced through the skin and body wall into the target organ under ultrasound guidance. The biopsy needle is fired to obtain a core sample of tissue. The sample is then placed in formalin for histopathologic evaluation.

The liver is the most common target for ultrasound-guided biopsy in avian patients. The liver is large, accessible, and frequently affected by disease. The biopsy needle is advanced through the ventral body wall into the liver parenchyma under ultrasound guidance. The needle should be directed away from the gallbladder and major hepatic vessels to reduce the risk of hemorrhage or bile leakage.

The coelomic cavity should be evaluated for the presence of free fluid before performing an ultrasound-guided procedure. Free fluid may indicate coelomic effusion, which increases the risk of complications. The presence of free fluid may also provide an opportunity for diagnostic abdominocentesis, which can be performed with ultrasound guidance to avoid puncturing organs.

Ultrasound-guided procedures require careful patient preparation and monitoring. The bird should be fasted for several hours before the procedure to reduce the risk of regurgitation and aspiration. The bird should be positioned in dorsal recumbency with the ventral coelomic region exposed. The skin over the puncture site should be prepared aseptically.

The bird should be monitored closely during and after the procedure for signs of hemorrhage, respiratory distress, or other complications. The bird should be kept warm and quiet after the procedure to minimize stress and reduce the risk of complications. The owner should be instructed to monitor the bird for signs of lethargy, anorexia, or respiratory distress for 24 to 48 hours after the procedure.

## Common Artifacts and Limitations

Air is the primary limitation of avian ultrasonography. The air sac system and air-filled lungs create acoustic shadowing that obscures organs positioned behind them. The liver is the primary acoustic window because it displaces the air sacs ventrally and transmits sound waves well. Organs that are not adjacent to the liver, such as the dorsal aspects of the kidneys, are difficult to evaluate.

Reverberation artifacts are common in avian ultrasound because of the multiple air-tissue interfaces within the coelomic cavity. Reverberation appears as multiple, equally spaced, hyperechoic lines that extend from the air-tissue interface. These artifacts can obscure underlying structures and make interpretation difficult.

Acoustic shadowing is caused by structures that reflect or absorb sound waves completely. The ventriculus with its dense muscular wall and gritty contents creates acoustic shadowing that obscures structures positioned behind it. The keel bone and other bony structures also create acoustic shadowing.

The small size of avian organs limits the resolution of ultrasound images. High-frequency transducers provide better resolution but have limited penetration. The depth of penetration decreases as the frequency increases, which limits the use of very high-frequency transducers in larger birds. The operator must balance the need for resolution against the need for penetration.

The normal sonographic appearance of avian organs varies by species. The size, shape, and echogenicity of organs differ between species and between individuals within a species. The operator must be familiar with the normal anatomy of the species being examined to interpret the images accurately.

The lack of species-specific reference values for many avian ultrasound measurements limits the interpretation of findings. A study of jejunal wall thickness in chickens found a mean thickness of 2.1 mm, but the study did not find a correlation with body weight [11]. This finding highlights the need for species-specific reference values and suggests that extrapolation from other species may not be appropriate.

The ultrasound examination is operator-dependent, and the quality of the images depends on the skill and experience of the operator. The operator must be able to recognize normal anatomy, identify artifacts, and obtain images in the correct planes. Training and experience are essential for accurate interpretation of avian ultrasound images.

## Comparison with Other Imaging Modalities

Radiography is the most commonly used imaging modality in avian medicine because it is widely available, relatively inexpensive, and provides excellent detail of bony structures and air-filled organs. Radiography is useful for evaluating the respiratory system, the skeletal system, and the presence of metallic foreign bodies. However, radiography provides limited soft tissue detail, and the air sac system can obscure soft tissue structures.

Ultrasonography provides superior soft tissue detail compared with radiography and is particularly useful for evaluating the liver, gastrointestinal tract, and reproductive organs. Ultrasound provides real-time imaging, which allows the operator to evaluate organ movement and blood flow. Ultrasound does not use ionizing radiation, which makes it safe for serial monitoring of chronic conditions.

Computed tomography provides excellent detail of both bony and soft tissue structures and is not limited by air interfaces. Computed tomography is particularly useful for evaluating the respiratory system, the skeletal system, and the coelomic cavity. However, computed tomography requires general anesthesia and specialized equipment that may not be available in general practice.

A study comparing computed tomography and high-resolution ultrasound for the evaluation of brain tumors in dogs found that ultrasound was able to define tumor location, size, and geometry in tumors that were missed or incompletely imaged by computed tomography [9]. The study found that all tumors were hyperechoic on ultrasound, and secondary characteristics such as hemorrhage, cyst formation, and necrosis were more accurately defined by ultrasound compared with computed tomography [9]. This study demonstrates the complementary nature of these imaging modalities.

Magnetic resonance imaging provides the best soft tissue detail of any imaging modality but requires specialized equipment and general anesthesia. Magnetic resonance imaging is rarely used in avian medicine because of the small size of avian patients and the limited availability of equipment. The long acquisition times and the need for specialized coils limit the use of magnetic resonance imaging in birds.

Endoscopy provides direct visualization of the coelomic cavity and allows for biopsy of visible lesions. Endoscopy requires general anesthesia and specialized equipment, and the procedure is invasive compared with ultrasound. Endoscopy is particularly useful for evaluating the respiratory system and the coelomic cavity, but it does not provide information about the internal structure of organs.

The choice of imaging modality depends on the suspected disease process, the stability of the patient, and the equipment available. Ultrasound is often the first choice for evaluating soft tissue structures in the coelomic cavity because it is noninvasive, does not require general anesthesia, and provides real-time imaging. Computed tomography and magnetic resonance imaging are reserved for cases where ultrasound is inconclusive or where the disease process requires cross-sectional imaging.

## Clinical Decision-Making and Escalation Criteria

The decision to perform ultrasonography in an avian patient should be based on the history, physical examination findings, and results of other diagnostic tests. Ultrasound is indicated when there is suspicion of disease affecting the liver, gastrointestinal tract, reproductive organs, or kidneys. Ultrasound is also indicated for monitoring known conditions and for guiding interventional procedures.

The American Veterinary Medical Association recommends that pet birds receive regular veterinary examinations to maintain health and detect disease early [1]. The World Small Animal Veterinary Association provides global guidelines for companion animal care, including preventive care and clinical guidance [3]. These guidelines emphasize the importance of diagnostic testing when clinical signs suggest disease.

The American Animal Hospital Association provides practice guidance for companion animal care, including preventive care and life-stage considerations [2]. These guidelines emphasize the importance of tailoring diagnostic testing to the individual patient and the clinical situation. The decision to perform ultrasound should be based on the clinical judgment of the veterinarian and the needs of the individual patient.

The World Organisation for Animal Health provides official guidance on animal health and welfare, including surveillance and reporting requirements [6]. These guidelines emphasize the importance of accurate diagnosis and reporting of notifiable diseases. Ultrasound can contribute to the diagnosis of diseases that may have public health or trade implications.

The Cornell University College of Veterinary Medicine provides educational resources for veterinarians and animal owners [5]. These resources emphasize the importance of evidence-based medicine and the use of diagnostic testing to guide treatment decisions. The Merck Veterinary Manual provides authoritative information on avian diseases and diagnostic techniques [4].

Veterinarians should escalate to advanced imaging or referral when ultrasound findings are inconclusive or when the disease process requires specialized expertise. Computed tomography or magnetic resonance imaging may be indicated when ultrasound cannot fully evaluate the coelomic cavity because of air interfaces or when the disease process involves bony structures. Referral to a specialist may be indicated for complex cases or for procedures that require specialized equipment or expertise.

Veterinarians should escalate to emergency care when the bird shows signs of respiratory distress, severe hemorrhage, or other life-threatening conditions. The bird should be stabilized before diagnostic testing is performed. The owner should be instructed to seek emergency veterinary care if the bird's condition deteriorates.

## Record Keeping and Documentation

Accurate record keeping is essential for avian ultrasonography. The ultrasound images should be saved and stored in the patient's medical record. The images should be labeled with the patient's identification, the date of the examination, and the transducer and settings used. The images should be reviewed and interpreted by the veterinarian performing the examination.

The ultrasound report should include a description of the patient, the indication for the examination, the findings, and the interpretation. The report should describe the sonographic appearance of each organ evaluated, including the size, shape, echogenicity, and echotexture. The report should note any abnormalities and the location and characteristics of any lesions.

The ultrasound report should include a comparison with previous examinations when available. The report should note any changes in the size, shape, or echogenicity of organs or lesions. The report should include recommendations for further diagnostic testing or treatment based on the findings.

The ultrasound report should be communicated to the owner in a clear and understandable manner. The owner should be informed of the findings, the implications for the bird's health, and the recommended next steps. The owner should be instructed to monitor the bird for specific signs and to return for follow-up examinations as recommended.

The ultrasound images and report should be retained in the patient's medical record for future reference. The images should be stored in a format that can be retrieved and reviewed at a later date. The report should be updated as new information becomes available or as the patient's condition changes.

## Common Failure Patterns and Troubleshooting

Poor image quality is the most common problem encountered in avian ultrasonography. The most common cause of poor image quality is inadequate coupling between the transducer and the patient's skin. Feathers must be parted or plucked to expose the skin, and coupling gel must be applied generously. Air bubbles in the coupling gel can create artifacts that degrade image quality.

Inadequate transducer frequency is another common cause of poor image quality. Low-frequency transducers provide inadequate resolution for the small structures of avian patients. High-frequency transducers, typically 10 to 18 MHz, are required for adequate resolution. The operator should select the highest frequency transducer that provides adequate penetration for the target structure.

Incorrect machine settings can degrade image quality. The depth should be set to the minimum that allows visualization of the target structure. The gain should be adjusted to produce a uniform image without excessive brightness or shadowing. The focus should be set at the level of the target structure to optimize lateral resolution.

Patient movement is a common cause of image degradation. The bird should be restrained securely to minimize movement during the examination. Sedation or anesthesia may be required for uncooperative patients. The examination should be completed as quickly as possible to minimize stress and heat loss.

Air artifacts are a common limitation of avian ultrasonography. The air sac system and air-filled lungs create acoustic shadowing that obscures organs positioned behind them. The operator should use the liver as the primary acoustic window and should angle the transducer to avoid air-filled structures when possible.

The inability to identify a specific organ is a common problem in avian ultrasonography. The operator should be familiar with the normal anatomy of the species being examined and should use systematic scanning techniques to identify organs. The operator should use landmarks such as the liver, the ventriculus, and the synsacrum to orient the examination.

## Welfare and Safety Considerations

The welfare of the avian patient should be a primary consideration during ultrasonography. The examination should be performed as quickly as possible to minimize stress and heat loss. The bird should be handled gently and securely to prevent injury. The bird should be monitored closely for signs of distress, such as increased respiratory rate, vocalization, or struggling.

Hypothermia is a significant risk in small birds during ultrasonography. The bird should be positioned on a warm surface, and the ambient temperature of the examination room should be increased. The feathers should not be plucked unnecessarily, and the examination should be completed as quickly as possible. The bird should be warmed after the examination if hypothermia is suspected.

Stress is a significant concern in avian patients. The bird should be handled in a quiet, dimly lit room to minimize stress. The bird should be allowed to acclimate to the examination room before the procedure. The bird should be monitored for signs of stress, such as increased respiratory rate, vocalization, or struggling.

The use of sedation or anesthesia should be considered for uncooperative patients or for prolonged examinations. The choice of sedation protocol depends on the species, the patient's condition, and the anticipated duration of the examination. The bird should be monitored closely during and after sedation or anesthesia.

The ultrasound machine should be maintained and calibrated regularly to ensure optimal image quality. The transducer should be inspected for damage and cleaned after each use. The coupling gel should be warmed before use to minimize heat loss.

The veterinarian should follow standard precautions to prevent the transmission of zoonotic diseases. Gloves should be worn when handling birds and when performing ultrasound-guided procedures. The ultrasound machine and transducer should be cleaned and disinfected after each use.

## At a Glance

| Aspect | Recommendation | Clinical Rationale |
|--------|----------------|-------------------|
| Transducer selection | Linear array, 10 to 18 MHz for most avian patients | High frequency provides adequate resolution for small avian organs, linear array provides excellent near-field resolution for superficial structures |
| Patient positioning | Dorsal recumbency with ventral coelomic region exposed | Provides access to the ventral midline, the primary acoustic window for the liver, gastrointestinal tract, and reproductive organs |
| Primary acoustic window | Liver | The liver displaces the air sacs ventrally and transmits sound waves well, allowing evaluation of adjacent organs |
| Jejunal wall thickness reference | Mean 2.1 mm in healthy chickens | Species-specific reference value, body weight does not predict jejunal wall thickness in chickens [11] |
| Common limitation | Air sac system creates acoustic shadowing | Air-filled structures reflect sound waves completely, obscuring organs positioned behind them |
| Escalation criterion | Advanced imaging or referral when ultrasound is inconclusive | Computed tomography or magnetic resonance imaging may be needed when air interfaces limit ultrasound evaluation |

## Practical Implementation Steps

The following steps outline a systematic approach to performing ultrasonography in avian patients:

1. Review the patient's history and physical examination findings to determine the indication for ultrasound and the target organs.
2. Select the appropriate transducer based on the size of the patient and the target organs. Use a linear array transducer with a frequency of 10 to 18 MHz for most avian patients.
3. Prepare the patient by parting or plucking the feathers over the ventral coelomic region. Position the bird in dorsal recumbency on a warm surface.
4. Apply warm coupling gel to the transducer and the patient's skin. Adjust the machine settings, including depth, gain, and focus, to optimize image quality.
5. Perform a systematic examination of the coelomic cavity, starting with the liver and moving caudally to evaluate the gastrointestinal tract, reproductive organs, and kidneys.
6. Document the findings with saved images and a written report. Communicate the findings to the owner and recommend appropriate next steps.

## Records and Measurements

The following measurements should be recorded during avian ultrasonography:

| Measurement | Normal Finding | Clinical Significance |
|-------------|----------------|----------------------|
| Liver size | Should not extend beyond the caudal border of the sternum | Hepatomegaly suggests liver disease |
| Jejunal wall thickness | Mean 2.1 mm in healthy chickens [11] | Thickening suggests gastrointestinal disease |
| Ovarian follicle size | Varies with reproductive status | Enlarged follicles suggest reproductive activity or disease |
| Testicular size | Varies with reproductive status | Enlarged testes suggest reproductive activity or neoplasia |
| Kidney size | Should not extend beyond the borders of the synsacrum | Renomegaly suggests kidney disease |
| Spleen size | Should not exceed the size of the proventriculus | Splenomegaly suggests systemic disease |

## Frequently Asked Questions

### What transducer frequency is recommended for avian ultrasonography?

Linear array transducers with frequencies between 10 and 18 MHz are recommended for most avian patients. High-frequency transducers provide the resolution needed to evaluate the small organs of birds. The operator should select the highest frequency transducer that provides adequate penetration for the target structure.

### How should a bird be positioned for coelomic ultrasonography?

The bird should be positioned in dorsal recumbency with the ventral coelomic region exposed. The feathers over the ventral midline should be parted or plucked to allow direct contact between the transducer and the skin. The bird should be positioned on a warm surface to minimize heat loss.

### What is the primary acoustic window in avian ultrasonography?

The liver is the primary acoustic window in avian ultrasonography. The liver displaces the air sacs ventrally and transmits sound waves well, allowing evaluation of adjacent organs. The operator should use the liver as a starting point for the systematic examination of the coelomic cavity.

### What is the normal jejunal wall thickness in chickens?

The mean jejunal wall thickness in healthy chickens is 2.1 mm, with a standard error of 0.08 mm [11]. A study of 89 clinically normal chickens found no statistically significant correlation between body weight and jejunal wall thickness [11]. Species-specific reference values are needed for accurate interpretation.

### What are the main limitations of avian ultrasonography?

The air sac system is the main limitation of avian ultrasonography. Air-filled structures create acoustic shadowing that obscures organs positioned behind them. The small size of avian organs limits resolution, and the lack of species-specific reference values limits interpretation of findings.

### Can ultrasound be used to guide biopsy procedures in birds?

Yes, ultrasound can be used to guide aspiration and biopsy procedures in birds. The real-time nature of ultrasound allows the operator to visualize the needle tip as it enters the target organ, reducing the risk of complications. The liver is the most common target for ultrasound-guided biopsy in avian patients.

### When should advanced imaging be considered in avian patients?

Advanced imaging should be considered when ultrasound findings are inconclusive or when the disease process requires cross-sectional imaging. Computed tomography provides excellent detail of bony and soft tissue structures and is not limited by air interfaces. Referral to a specialist may be indicated for complex cases.

### What are the welfare considerations for avian ultrasonography?

Hypothermia and stress are the primary welfare considerations for avian ultrasonography. The bird should be positioned on a warm surface, and the examination should be completed as quickly as possible. The bird should be handled gently and monitored closely for signs of distress.

## Related Veterinary Guides

- [Ultrasonography of the Equine Abdomen: Indications and Findings](/knowledge/veterinary-medicine/diagnostic-imaging/ultrasonography-equine-abdomen-indications-findings)
- [Avian Diagnostic Imaging: Radiography and Ultrasonography in Birds](/knowledge/veterinary-medicine/backyard-poultry/avian-diagnostic-imaging-radiography-ultrasonography-birds)
- [Abdominal Ultrasound in Cats: Normal Findings and Common Abnormalities](/knowledge/veterinary-medicine/diagnostic-imaging/abdominal-ultrasound-cats-normal-findings-common-abnormalities)
- [Thoracic Radiography in Exotic Pets: Techniques and Normal Anatomy](/knowledge/veterinary-medicine/diagnostic-imaging/thoracic-radiography-exotic-pets-techniques-normal-anatomy)
- [Ultrasound of the Canine and Feline Gastrointestinal Tract: Normal and Abnormal Findings](/knowledge/veterinary-medicine/diagnostic-imaging/ultrasound-canine-feline-gastrointestinal-tract-normal-abnormal-findings)

## References and Further Reading

- [Pet Care](https://www.avma.org/resources-tools/pet-owners). American Veterinary Medical Association.
- [AAHA Guidelines](https://www.aaha.org/resources). American Animal Hospital Association.
- [Global Guidelines](https://wsava.org/global-guidelines). World Small Animal Veterinary Association.
- [Merck Veterinary Manual](https://www.merckvetmanual.com/). Merck Veterinary Manual.
- [Cornell University College of Veterinary Medicine](https://www.vet.cornell.edu/). Cornell University.
- [Animal Health and Welfare](https://www.woah.org/en/what-we-do/animal-health-and-welfare). World Organisation for Animal Health.
- [Ultrasound biomicroscopy and tonometry in ophthalmologically normal pigeon eyes.](https://pubmed.ncbi.nlm.nih.gov/28074538). Veterinary ophthalmology, 2017.
- [Hyolaryngeal Movement During Normal and Effortful Swallows Determined During Ultrasonography.](https://pubmed.ncbi.nlm.nih.gov/37668547). Journal of speech, language, and hearing research : JSLHR, 2023.
- [Correlation of neuropathologic findings, computerized tomographic and high-resolution ultrasound scans of canine avian sarcoma virus-induced brain tumors.](https://pubmed.ncbi.nlm.nih.gov/3031228). Journal of neuro-oncology, 1987.
- [High-frequency ultrasound, computed tomography and computed tomography arthrography of the cranial cruciate ligament, menisci and cranial meniscotibial ligaments in 10 radiographically normal canine cadaver stifles.](https://pubmed.ncbi.nlm.nih.gov/31088469). BMC veterinary research, 2019.
- [Ultrasound evaluation of small intestinal thickness and a comparison to body weight in normal chickens (Gallus gallus domesticus).](https://pubmed.ncbi.nlm.nih.gov/30693498). Australian veterinary journal, 2019.

> This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.