Radiographic Findings in Sickle Cell Disease

Frontal and lateral views of an 11-year-old girl's chest are shown here (Figure 1). What are the findings in the lungs?

A. None. The lungs are normal.

B. Diffuse, faint reticular opacities.

C. Small pleural effusion.

Excluding the central line, these images demonstrate evidence for involvement of 3 organ systems. What are they?

A. GI, skin, and genitourinary.

B. Cardiovascular, GI, and bone.

C. Cardiovascular, genitourinary, and bone.

An image from the patient's MRI brain scan is shown in Figure 2. It demonstrates expansion of what space?

A. Subdural.

B. Subarachnoid.

C. Diploic.

(Answers and discussion begin on the next page.)

Figure 1 shows the frontal and lateral views of an 11-year-old girl's chest. What are the findings in the lungs?

It is always tempting to find something on the chest radiograph that might explain a patient's symptoms. In this instance, however, there are no pathological findings in the lung parenchyma.

A is the correct choice. The lungs appear normal.

These images demonstrate evidence for involvement of which 3 organ systems?

These images provide us with 3 clues about this child's underlying medical condition. First, her cardiac silhouette is a little too generous. On the frontal upright anteroposterior view, her greatest cardiac diameter is 60% of her greatest thoracic diameter. By age 11 and by the looks of her superior mediastinum, this enlarged appearance cannot be attributed to a prominent thymus. (By approximately age 10, the thymus should no longer appear particularly noticeable on a child's chest radiograph.¹) The lateral view confirms the cardiomegaly: the posterior heart border extends quite close to the anterior aspect of the thoracic vertebral bodies.

Possible causes of an enlarged heart in a child include cardiomyopathy, pericardial effusion, high-flow vascular lesions, renal disease, anemia, and congenital heart disease. Congestive heart failure seems unlikely in this case because the pulmonary arteries and veins are normal and there is no pleural effusion. In this child's case, anemia with elevated cardiac output is the culprit, as evidenced by the cardiomegaly.

The second clue to the diagnosis is found in the bones on the lateral view: note the sclerosis and irregular indentation of the vertebral endplates. This is apparent on all of the visualized thoracic and lumbar vertebral bodies and must therefore reflect a diffuse, systemic process rather than something focal, such as trauma or osteomyelitis. In this case, the multiply-affected endplates represent the chronic appearance of vascular insufficiency and/or avascular necrosis.

The third clue is found on the frontal view. A small surgical clip can be seen in the soft tissues of the right upper quadrant--evidence that a surgeon has probably absconded with this patient's gallbladder.

B is the correct choice. There is cardiovascular, GI, and bone involvement.

A fourth clue is the implantable port beneath the patient's skin placed to provide intravenous access when necessary (although technically this is part of the cardiovascular system).

The patient has sickle cell disease.

(Continued on page 606.)

An image from the patient's MRI brain scan (Figure 2) demonstrates expansion of what space?

This is a T1-weighted image of the same child's brain obtained in the sagittal plane. On a T1-weighted sequence, fat is bright and fluid is dark. The subdural and subarachnoid spaces are normal.

Look closely at the occiput; under the bright stripe that reflects the normal subcutaneous fat of the scalp's skin, there is a broad, dark stripe that represents noticeable widening of the diploic space (C). This is a common feature in children with sickle cell disease and is the result of compensatory hematopoiesis. In a healthy child, we would expect that space to be more narrow and also fatty--and therefore bright on T1-weighted images. Instead, the dark, fluid-like signal characteristics of this diploic marrow confirm that this is active, hematopoietic marrow. This preservation of red marrow and failure to convert to fatty marrow is seen in many areas of the skeleton of a patient with sickle cell disease and often persists throughout a patient's lifetime.³

Other typical osseous findings of sickle cell disease include avascular necrosis of the humeral and femoral heads; intramedullary bone infarctions almost anywhere, including the ribs and bones of the hands; and osteomyelitis. Osteomyelitis is a less common event in sickle cell patients than bone infarction, but it may be very difficult to differentiate the 2 entities because there is a significant degree of overlap in clinical, radiological, and laboratory findings.³ Causative organisms of osteomyelitis in this patient population include Salmonella,Staphylococcus aureus, and assorted Gram-negative enteric bacilli.³

Figure 3 shows an earlier chest radiograph from this same child. It was taken 2 years earlier, when she presented with fever, hypoxia, and chest pain. At that time, a diagnosis of acute chest syndrome (ACS) was made. A nuclear medicine bone scan obtained at that time (Figure 4) revealed a mottled appearance of the ribs, reflecting alternating areas of increased or decreased uptake of the radiotracer by the osteoblasts, consistent with scattered bone infarcts of the ribs of varying ages. The calvarium is thickened on the bone scan too--a finding consistent with expansion of the diploic space.

Acute Chest Syndrome

ACS remains a common cause of morbidity and mortality among patients with sickle cell disease. Recurrent episodes are frequent. Thus, ACS is a leading cause of hospitalization--and is often cited as the leading cause of death--in children with this disease.^2,4 The diagnosis is made by identifying a new infiltrate on radiographs, along with dyspnea, fever, leukocytosis, cough, pain, or hypoxia.^2-4

ACS is generally thought to be a multifactorial entity caused by various combinations of infection, rib infarction, chest splinting from pain, and thromboembolic events to the lungs.^1-3 The pulmonary intravascular events include in situ thrombosis with sickling, acute and chronic thrombi, and fat emboli originating from bone infarctions.⁴

Most cases of ACS do not have a clear cause. When infection appears to be the predominant process, the common pathogens include Streptococcus pneumoniae, Haemophilus influenzae, S aureus, Chlamydia pneumoniae, and Salmonella.^3,4 Chest radiographs commonly show multifocal disease, especially in the lower lobes.³ Differentiating between infection and infarction in the lung may be difficult. Some reports suggest that an upper lobe process is more likely to represent an infection, whereas lower lobe processes may be more likely to represent infarction.⁴

ACS places patients at increased risk for the chronic pulmonary manifestations of sickle cell disease, which include pulmonary hypertension, ventilatory compromise, and cor pulmonale.¹ Pulmonary hypertension in children with sickle cell disease is associated with significant morbidity; pulmonary hypertension in adults with sickle cell disease has high rates of both morbidity and mortality.⁵ *

References:

REFERENCES:

1.

Kirks D. Respiratory system. In: Kirks DR, Griscom NT.

Practical Pediatric Imaging: Diagnostic Radiology of Infants and Children.

3rd ed. Philadelphia: Lippincott-Raven; 1998: 619-819.

2.

Melton CW, Haynes J Jr. Sickle acute lung injury: role of prevention and early aggressive intervention strategies on outcome.

Clin Chest Med.

2006;27:487-502.

3.

Lonergan GJ, Cline DB, Abbondanzo SL. Sickle cell anemia.

Radiographics.

2001;21:971-994.

4.

Martin L, Buonomo C. Acute chest syndrome of sickle cell disease: radiographic and clinical analysis of 70 cases.

Pediatr Radiol.

1997;27:637-641.

5.

Onyekwere OC, Campbell A, Teshome M, et al. Pulmonary hypertension in children and adolescents with sickle cell disease.

Pediatr Cardiol.

2007 Aug 7; [Epub ahead of print].