Radiology

Kiran M. Sargar

William H. McAlister

ORDERING A RADIOLOGY EXAMINATION

Imaging procedures may be requested depending on the clinical condition of the patient. Recommendations for imaging may represent either optimal selection (based on availability) or complementary examinations that build on each other.
The radiologist may customize the examination or even suggest a different one to answer the specific clinical question. Key information should be provided:
- Radiologic procedure requested
- Specific clinical question or clinical situation
  - Gastrointestinal (GI) conditions (see Table 25-1)
  - Other conditions (see Table 25-2)
- Relevant clinical history, diagnoses, and surgeries
  - Cancer patients: last chemotherapy or radiation therapy
- Prior imaging studies and the reports (especially if studies were performed elsewhere)
- Allergy to iodinated intravenous (IV) contrast
- Renal function (serum creatinine) if IV contrast is to be used
- IV access (location and gauge)
- Patient factors: stability (examination at bedside or in radiology department), nothing by mouth (NPO) status, mechanical ventilation, cooperativeness, and need for sedation

Safety Considerations

Monitored conscious sedation with agents such as IV pentobarbital, midazolam, or propofol is appropriate for young patients who cannot stay still, for uncooperative patients, and for potentially painful procedures.
Make patients NPO when ordering any sedated examination, computed tomography (CT) that involves IV contrast, MRI with IV contrast, or a GI fluoroscopic examination.

Radiation Considerations

Radiography, fluoroscopy, and CT expose the patient to ionizing radiation, whereas ultrasound and magnetic resonance imaging (MRI) do not.
At children’s hospitals and imaging centers, radiation doses can be, and often are, significantly reduced by modification of imaging technique.

Gastrointestinal Contrast Considerations

Barium and water-soluble contrast agents
- Barium is usually the GI contrast of choice but should not be used if a leak is suspected because it can cause peritonitis or mediastinitis or if surgery is imminent. Also, barium can limit future abdominal CT imaging because of scatter artifact from retained material.
- Water-soluble ionic contrast agents (e.g., Hypaque, Gastroview) are used when barium is contraindicated. Their advantage over barium is that they reabsorb from body cavities, but the disadvantage is that image quality is poorer.
  - They are hyperosmolar and may cause fluid shifts into the GI tract. This is usually well tolerated by the patient.
  - They should not be used when large volume aspiration is a possibility, as they may cause pulmonary edema.
- Water-soluble nonionic low-osmolar contrast agents (e.g., Omnipaque, Optiray) may be used orally in infants when the risk of aspiration is high or when GI leak is suspected. Nonionic contrast agents can be diluted to make them isotonic and still produce satisfactory image quality.

TABLE 25-1 Gastrointestinal Conditions: Recommended Imaging

Condition	Imaging used
Necrotizing enterocolitis	Serial abdominal radiographs every 4-6 hr may demonstrate pneumatosis, free peritoneal air, and portal vein gas.
Intussusception	Obstructive series may be useful in suggesting (mass effect) or excluding (air or stool in right colon and terminal ileum). Ultrasound should establish the diagnosis.
Malrotation	Obstructive series is usually normal unless midgut volvulus is present; upper gastrointestinal (GI) study is required. Urgent imaging is a must.
Appendicitis	Abdominal radiographs are often nonspecific, although occasionally appendicoliths may be seen (15%). Ultrasound is imaging study of choice in young, thin children. Computed tomography (CT) is study of choice in older children with moderate body fat. Typically, intravenous contrast is used. MRI can be used to diagnose appendicitis.
Bowel perforation	Obstructive series may show free air. Erect and decubitus radiographs are needed. CT may be useful in demonstrating small amounts of free air and suggesting a cause.
Pyloric stenosis	Ultrasound is procedure of choice, which shows the thickened pyloric muscle. Upper GI examination is comparable.
Esophageal atresia/tracheoesophageal fistula	Chest and abdominal radiographs may show dilated proximal pouch and coiled proximal nasogastric tube. Abdominal gas is seen in atresia with tracheoesophageal fistula, while absence of abdominal gas indicates atresia without fistula. Upper GI is the study of choice for looking for “H-type” fistula. It is associated with VACTERL (vertebral, anorectal, cardiac, tracheoesophageal, renal and limb anomalies).
Duodenal atresia	Abdominal radiograph is diagnostic (distended stomach and proximal duodenum with an otherwise gasless abdomen).
Meckel diverticulum	Often difficult to diagnose. Nuclear medicine “Meckel scan” may demonstrate ˜80%-90% sensitivity and 90%-95% specificity if there is gastric mucosa. CT with oral and IV contrast or MRI may demonstrate diverticulum.
Biliary atresia	Ultrasound is useful to assess for presence of the gallbladder and its size (often < 1.5 cm) as well as to exclude biliary obstruction from choledochal cysts. “Triangular cord sign,” which is tubular echogenic cord of fibrous tissue at porta hepatis. HIDA scan is useful in diagnosing obstruction.
Ascites	Ultrasound can diagnose and localize for drainage.
Inflammatory bowel disease	MR enterography is preferred over small bowel follow-through and useful to evaluate extent and degree of bowel inflammation and complications like abscess, fistula, and stricture. Diffusionweighted MRI can distinguish acute vs. chronic inflammation.
Neuroblastoma	CT is recommended for initial staging and shows heterogeneous mass with enhancement and calcifications. The mass often crosses the midline and encases the vessels. CT is also helpful to asses osseous and liver metastasis. MRI is useful to evaluate intraspinal extension of the mass. MIBG scan is helpful to detect metastatic disease.
Wilms tumor	It is the most common renal malignancy in young children, and CT scan of chest and abdomen is done for initial staging. CT scan reveals enhancing renal mass, which tends to displace the adjacent vessels. Calcifications are rare, and it can extend along the renal vein. Lung metastases are common at presentation. MRI can be used for abdominal involvement.
Hepatoblastoma	It is the most common pediatric hepatic malignancy. US shows heterogeneous mass in the liver with moderate vascularity and mass effect. CT scan reveals predominantly hypodense mass, which can contain calcification. CT as well as MRI are accurate to assess the extent of liver involvement, portal vein invasion, and lymph nodal metastasis.
Henoch-Schonlein purpura	Most common pediatric vasculitis. US is helpful to assess the bowel involvement and shows bowel wall thickening, gall bladder hydrops, scrotal involvement, and complications like intussusception. MRI and CT can be used.
Adrenal hemorrhage	Most common in neonates and US is the first modality to evaluate and show heterogeneous suprarenal mass without vascularity. Follow-up US after 3-4 weeks reveals resolution or decrease in size of the mass, helping to exclude neuroblastoma. MRI is useful to confirm hemorrhage in equivocal cases and helps to exclude neuroblastoma.

TABLE 25-2 Selected Nongastrointestinal Conditions: Recommended Imaging

Condition	Imaging used
Stridor/croup, epiglottitis	Frontal and lateral soft tissue neck and chest radiographs show steeple sign of croup and the thumb sign of epiglottitis.
Pleural effusion	Frontal and lateral chest radiographs may be sufficient. Decubitus radiographs may demonstrate fluid mobility. Use ultrasound if they are inconclusive or localization for drainage is required. Use computed tomography (CT) with contrast if there is concern for empyema, loculated fluid, or necrotizing pneumonia.
Pulmonary embolism	CT with pulmonary embolism protocol is necessary, which requires excellent intravenous (IV) access for contrast. If such CT is not available, nuclear ventilation-perfusion scan is a less specific option.
Orbital cellulitis	Orbital CT with IV contrast
Abdominal trauma	CT with IV contrast is the study of choice.
Thoracic trauma	CT with IV contrast is the study of choice. In patients with minor trauma, chest radiographs may be useful.
Head trauma, epidural/subdural hematoma	CT with and without IV contrast is used, with magnetic resonance imaging (MRI) if CT is inconclusive.
Stroke	CT without IV contrast is used to evaluate for bleeding and edema, MRI without contrast and magnetic resonance arteriogram for suspected hemorrhagic etiology, and for patient with sickle cell disease.
Extremity deep vein thrombosis	Use venous ultrasound with Doppler.
Ventriculoperitoneal shunt malfunction	Shunt series (radiographs of skull, chest, and abdomen) to access for discontinuity is useful, with noncontrast head CT to evaluate hydrocephalus.
Retropharyngeal abscess	Soft tissue neck AP and lateral radiographs for initial evaluation. Typically, CT neck with IV contrast is used to further identify.
Cervical spine trauma	Anteroposterior (AP) and lateral cervical spine radiographs (also odontoid view in children >age 6 years) are useful. Use CT if there is still question of fracture. If there is concern for ligamentous injury, flexion and extension lateral radiographs or MRI without contrast are necessary.
Scoliosis	Use scoliosis survey (AP total spine radiograph), adding lateral view if significant scoliosis, lordosis, or kyphosis.
Developmental dysplasia of the hip	Imaging is not preferable until patient is at least age 2 wk; earlier imaging is often inconclusive because of transient ligamentous laxity as a result of maternal hormones. Ultrasound is the study of choice until age 6 months. AP radiograph of the pelvis after age 6 months
Pyelonephritis	Use ultrasound for evaluation of acute pyelonephritis or complications of pyelonephritis, such as perinephric abscess or pyonephrosis. Contrast CT, and MRI are excellent for this diagnosis. Consider voiding cystourethrogram for evaluation of vesicoureteral reflux once infection has resolved.
Ovarian torsion	Pelvic ultrasound with Doppler to show enlarged ovary, decreased vascularity, and peripheral cysts in ovary
Testicular torsion	Scrotal ultrasound
Septic arthritis	Most common in hip, knee, and ankle joints. US is useful to diagnose the effusions. Effusions can be tapped under US or fluoroscopy guidance to obtain joint fluid for cytology and culture. MRI is useful.
Osteomyelitis	Radiographs are often negative in early acute osteomyelitis, and MRI is preferred for diagnosis of acute osteomyelitis, which shows marrow edema, cortical breaks, subperiosteal and subcutaneous and muscle tissue abscesses, fistulae, and sequestrum.
Slipped capital femoral epiphysis	Adolescent boys and girls. AP and frog leg radiographs show extent and severity of slip, which is medial and posterior.
Child abuse	Complete skeletal survey may show multiple fractures in various stages of healing, metaphyseal corner fractures, posterior rib fractures, sternal, complex skull, and phalangeal fractures, all of which are highly suggestive of child abuse. CT or MRI of the head is useful to assess intracranial hemorrhage and skull fractures.
Vascular and lymphatic malformations	US, CT, and MRI are useful to know the type of vascular and lymphatic malformation, extent of the lesion, and vascularity.
Skeletal dysplasias	Skeletal survey will help establish the diagnosis.
Langerhans cell histiocytosis (LCH)	Can affect single or multiple bones. Most common locations are skull, pelvis, femur, ribs, and humerus. On radiographs show lytic lesions with or without sclerotic rim. In the skull, lytic lesions have beveled edges. Floating tooth appearance may be seen. Vertebra plana or vertebral body compression deformity can be seen in the spine.
Cystic neck lesions	Thyroglossal duct cyst, dermoid, lymphatic malformation, and abscesses are the most common cystic lesions in the neck. US is preferred for initial evaluation of these cystic lesions.

Intravenous Contrast Considerations

The radiologist will help you determine appropriateness based on such factors as clinical indications and renal function.
Contrast power injectors provide optimal imaging for all CT scans, except for head CT scans, but these require a 22-gauge or larger needle, and preferably antecubital IV access. Hand IV lines and most of the central lines should be injected manually, which leads to suboptimal vessel opacification.
Contrast is relatively contraindicated in patients with renal insufficiency (elevated creatinine and GFR), sickle cell crisis, or prior major anaphylactic allergic reaction to contrast.
Patients with prior less severe contrast reactions may have IV contrast if premedicated.
- According to the ACR manual on contrast media recommendations, prednisone 0.5-0.7 mg/kg PO (maximum up to 50 mg) should be given 13 hours, 7 hours, and 1 hour prior to contrast injection. In addition, diphenhydramine 1.25 mg/kg PO (maximum up to 50 mg) should be given 1 hour prior to contrast injection.
- Appropriate IV drug doses may be substituted for patients who cannot ingest PO medication.

Magnetic Resonance Imaging Considerations

Contraindications to MRI include presence of programmable implanted devices (e.g., pacemakers, cochlear implants), MRI-noncompatible aneurysm clips, and metallic fragments in the eye. Compatibility must also be considered for other implants, prostheses, metal objects, and some dark tattoos.
Closed loop wires have a tendency to heat up during the examination. Skin staples are usually tolerated if they are taped securely.
Some stents, filters, coils, and prosthetic valves require 6-8 weeks to allow tissue ingrowth before an MRI may be performed.
IV gadolinium is contraindicated in patients with renal insufficiency due to risk of nephrogenic systemic fibrosis (NSF).
Patients usually must lie flat for 30-90 minutes or more and must be cooperative enough to lie still (or be sedated).

CHEST RADIOGRAPHY

Check for infiltrates, thickened bronchial walls, pulmonary edema, increased or decreased pulmonary vascularity, pleural effusions, pneumothorax, heart size, midline trachea, side of aortic arch, rib fractures, septal lines (Kerley B lines), etc.
Normal cardiothoracic ratio is 65% in infants and 55% in older children. A large thymic shadow is normal under the age of 2 years.
Check aeration. Flattened or inverted diaphragm on lateral view suggests air trapping.
Check for anomalies. Check on which side (left or right) the cardiac apex, aortic arch, stomach bubble, and liver shadow. Note any rib or vertebral anomalies.

Evaluating for Infiltrates

Check for subtle infiltrates behind the diaphragm and heart on the frontal view. Normally, the borders of the heart and diaphragm are sharp, and the right and left heart shadows should be similar in density. Right middle lobe and lingular infiltrates project over the heart on lateral and obscure the heart borders on AP radiographs (silhouette sign).
Infiltrates are present if the lung projecting over the spine does not become increasingly dark inferiorly on lateral radiograph (spine sign).
The normal thymus, which can be large and triangular in young children, is sometimes confused for upper lobe infiltrates, especially on the right.
Classic appearances of common entities
- Viral pneumonia/bronchiolitis: hyperinflation, perihilar infiltrates, and thickened bronchial walls (Fig. 25-1).
- Bacterial pneumonia: focal infiltrate, lobar consolidation with air bronchograms (Fig. 25-2), and parapneumonic pleural fluid.
- Atelectasis: linear opacities and volume loss.
- Round pneumonia: common in children below the age of 8 years due to incomplete development of collateral pathways. On radiographs, it appears as a circumscribed radiopacity with air bronchograms and tends to have slightly irregular margins. Superior segments of the lower lobes are the most common location.
- Acute chest syndrome (ACS): seen in sickle cell patients. Segmental, lobar, or multilobar consolidation with or without pleural effusion is seen on radiographs. The consolidation in ACS can progress rapidly, more so than in other bacterial
  pneumonias. Other radiographic signs of sickle cell disease can be seen such as cardiomegaly and vertebral endplate infarcts (H vertebra), aseptic necrosis of humeral heads, and a small, calcified spleen.
- The appearance of viral or bacterial infiltrates and atelectasis can be similar, especially in infants.

Figure 25-1 Viral bronchiolitis. Frontal view of the chest shows hyperinflation with perihilar infiltrates and peribronchial cuffing consistent with reactive airway disease. Notice associated subsegmental atelectasis in both lower lobes.