Lumbar and radial bone mineral density in children and adolescents with X-linked hypophosphatemia: evaluation with dual X-ray absorptiometry.

OBJECTIVE: To evaluate the bone mineral status of children being treated for X-linked hypophosphatemia, including potential differences between cortical bone in the radial diaphysis and combined cortical and trabecular bone in the lumbar spine. DESIGN AND PATIENTS: Forty-four bone mineral evaluations were performed in 11 children and adolescents with X-linked hypophosphatemia. Bone mineral density (BMD) of the lumbar spine and the radial diaphysis were measured by dual X-ray absorptiometry (DXA), second metacarpal cortical thickness was measured on hand radiographs, and these results were expressed as Z-scores (standard deviations from the mean). RESULTS: For the 11 initial examinations, Z-scores (mean+/-SD) were: radial BMD, -2.73+/-1.15, lumbar BMD, +1.28+/-1.53; and cortical thickness, -2.21+/-0.95. Lumbar BMD Z-scores were significantly greater than those for radial BMD and cortical thickness. On follow-up examinations there was a mild increase in radial BMD and decrease in lumbar BMD. Although these changes were statistically significant, they were quite small and the discordance between radial and lumbar BMD was not corrected. CONCLUSIONS: Children and adolescents who are being treated for X-linked hypophosphatemia manifest a bone mineral disorder characterized by decreased BMD in the appendicular skeleton and increased BMD in the lumbar spine. Although current therapy is successful in its anti-rachitic effects, it does not correct this bone mineral disorder and additional therapeutic trials should be considered.

Bone mineral disorders in children: evaluation with dual x-ray absorptiometry.

PURPOSE: To evaluate the utility of dual x-ray absorptiometry (DXA) in children with bone mineral disorders. MATERIALS AND METHODS: In phase 1, radial DXA was compared with single-energy photon absorptiometry (SPA) (n = 117). In phase 2, radial and lumbar bone mineral density (BMD) measured with DXA and second metacarpal cortical thickness were compared (254 examinations, 224 children). RESULTS: For radial BMD, DXA and SPA correlated well (r = .956) and SPA-equivalent values could be calculated from DXA measurements (mean residual error = 0.024 g/cm2). After controlling for age, sex, weight, and height, partial correlations were very small for lumbar BMD with radial BMD (r = .186) and lumbar BMD with cortical thickness (r = .158), and slightly better for radial BMD with cortical thickness (r = .544). Z scores also correlated poorly with no meaningful correlation for lumbar BMD with radial BMD (r = .07) CONCLUSION: In children with bone mineral disorders, radial DXA and SPA measurements correlate well. However, lumbar BMD, radial BMD, and cortical thickness correlate poorly and lumbar BMD frequently does not identify abnormality in patients with abnormal radial BMD. Lumbar BMD alone is not adequate for evaluation of bone mineral status in these patients.

Arterial and venous compromise by an osteochondroma.

A 9.5-year-old girl had popliteal arterial and venous compression by a distal femoral osteochondroma. Magnetic resonance imaging demonstrated the relation of the vessels to the osteochondroma and a three-phase bone scintigram showed asymmetry of arterial perfusion and evidence of venous stasis.

Massive jugular and dural sinus reflux associated with cerebral death.

Radionuclide cerebral angiograms demonstrated massive jugular venous reflux in two children with clinical and electroencephalographic evidence of cerebral death. With an antecubital injection, the tracer flowed up the jugular vein, through the transverse dural sinus, and down the contralateral jugular vein. No arterial flow was seen. We hypothesize that this unusual pattern reflects the absence of normal antegrade flow through the venous system. The appearance of jugular reflux is distinct from arterial flow and should not be confused with it. These cases illustrate communication between the systemic venous system and the dural sinuses. Although this pattern in not diagnostic of cerebral death, the appearance of radiotracer in the dural sinuses does not establish the presence of cerebral perfusion.

Glomerular filtration rate in children: validation and longitudinal use of determination from the 99mTc DTPA renogram.

The glomerular filtration rate (GFR) was estimated from the technetium diethylenetriaminepentacetic (99mTc DTPA) renogram by empirically correlating the renogram and clearance of the tracer as measured by plasma disappearance kinetics. To expand the potential application of this technique from its original description, minor changes in methodology were made; a new regression was generated with 30 subjects, and that formula was then validated prospectively. For the 50 children and adolescents in the prospective series whose GFR normalized for surface area (NGFR = GFR X 1.73 m2/SA; SA, surface area) was less than 120 mL/min/1.73 m2; renal function was estimated with a mean residual error of 8.0 mL/min/1.73 m2, and a mean relative error of 11%. These results are at least as good as those in the initial report, thus validating this method in a prospective series. To examine the use of this method longitudinally, 129 examinations were reviewed in 55 subjects who had NGFR estimated from the renogram (estimated) on at least two occasions. For 28 sets of serial examinations, NGFR was also measured by the plasma disappearance of 99mTc DTPA (measured). The true change in function for each set of serial examinations was defined as the increment for whichever method (estimation or measurement) was more stable. The mean longitudinal errors were 2.1 and 4.8 mL/min/1.73 m2 for measured and estimated NGFR, respectively. The increments in NGFR for these methods were correlated with a regression line near identity and r = .852. This indicates that a change in estimated NGFR reflects a change in measured NGFR of similar magnitude. This method can accurately estimate GFR from the 99mTc DTPA renogram, and it can be used longitudinally to follow children with renal disorders.

Radiopharmaceutical dosage selection for pediatric nuclear medicine.

To identify the most rational method for adjusting adult radiopharmaceutical dosages for children, four methods of dosage computation were examined from the perspectives of diagnostic adequacy and radiation absorbed dose. For static imaging, information density is the most important factor in study quality, and adjustment of dosage by body weight (Wt) for "thick" organs, and body surface area (BSA) for "thin" organs is recommended. Compared with adults, small children receive less radiation exposure if radiopharmaceutical dosages are adjusted by Wt, and slightly greater exposure if dosages are adjusted by BSA. For dynamic imaging studies, dosage requirements are governed by the spatial resolution needed for region of interest assignment, and the statistical reliability of the time-activity data. For dynamic renal imaging, renograms of similar quality are obtained if dosages are adjusted by height (Ht). Dynamic cardiac studies might appear to require dosages even larger than those adjusted by Ht which would result in higher radiation absorbed doses to pediatric patients. However, smaller dosages can be used in children by prolonging the imaging time and accepting lower temporal resolution. Dosage requirements for dynamic studies depend on which physiologic characteristics are measured from the time-activity data. Since the measurements of some characteristics demand higher count rates than others, dosage requirements ultimately depend on which measurements are clinically necessary. Close attention to the factors that determine these requirements may yield significant reduction in dosages, and thus in radiation exposure, for patients of all ages.

Secondary ossification center of transverse process: a bone-scan normal variant.

This report describes the bone-scan appearance of significantly increased activity in a lumbar transverse process of a 15-year-old boy; we believe it represents a normal variant related to the secondary ossification center.

Uterine hyperemia simulating rapid urinary excretion.

Uterine hyperemia in a menstruating adolescent girl was visualized on a renal transplant evaluation. This mimicked early excretion into the urinary bladder.

Diuretic radionuclide localization of upper urinary tract obstruction.

In 59 children with proved upper urinary tract obstruction diuretic radionuclide ureteral scans provided an accurate assessment of ureteral dilatation sufficient to distinguish ureteropelvic from ureterovesical obstruction. As a result, this test may be used instead of more invasive studies, such as retrograde or antegrade pyelography, to determine the site of obstruction in many cases of hydronephrosis.

Glomerular filtration rate in children: determination from the Tc-99m-DTPA renogram.

Analysis of the Tc-99m-DTPA renogram is usually limited to calculating the relative function of each kidney. To develop a method to determine the absolute glomerular filtration rate (GFR), various methods of analyzing the renogram were examined to determine which gave the best correlation with GFR. That regression could then be used to predict GFR without the need for blood samples. Fifty children were studied using Tc-99m-DTPA renograms and GFR measured simultaneously by plasma disappearance. The renogram variables were adjusted for detector sensitivity and for dose divided by weight, which was used as an index of plasma concentration. GFR correlated better with the slope of the second phase than with the area under the renogram curve. For the best correlation with GFR (using background subtraction and depth correction) r = .971 and the mean residual = 4.8 ml/min. For GFR normalized for body surface area (using background subtraction and no depth correction) r = .954 and the mean residual = 9.1 ml/min/1.73 m2. This method can accurately estimate GFR from the renogram in children.

Evaluation of obstructive uropathy with diuretic renography.

Diuretic renography has been recommended as a useful test to distinguish obstructed from dilated, but not obstructed, urinary systems. Twenty-four diuretic renograms were performed in 20 children, and a good correlation was found with other indicators of obstruction. The sensitivity for identifying obstruction was 83%, with a specificity of 94%. Severe hydroureteronephrosis may blunt or even mask the effect of diuresis on causing emptying of the tracer from the renal pelvis. Some kidneys did not drain well with the patient in a supine position but did empty with a change of position; these kidneys should be regarded as nonobstructed.

Diuretic radionuclide urography.

Diuretic radionuclide urography is a modification of conventional renography which utilizes the administration of intravenous furosemide to distinguish dilated, non-obstructed, hydronephrotic systems from those with significant mechanical obstruction. Diagnostic patterns are derived from computer generated time-activity histograms that depict the accumulation and washout of radiotracer before and after diuretic injection. In dilated but non-obstructed systems, diuresis produces a decline in activity. In obstructed systems, there is a failure of radiotracer washout in response to diuresis and no decline in activity is observed. The procedure is applicable to patients of all ages with suspected upper urinary tract obstruction. Clinical and experimental data support the accuracy and utility of this methodology and define its limitations and pitfalls.

Dual radiopharmaceutical imaging in congenital asplenia syndrome.

Asplenia was suspected in one patient with combined immunodeficiency syndrome and 5 with congenital cardiac anomalies who had Howell-Jolly bodies on peripheral blood smears. 99mTc-sulfur colloid scans were equivocal for absence of the spleen. When they were compared with the 99mTc-PIPIDA hepatobiliary images, a discrepancy in organ morphology between the two scans indicated that the spleen was present, whereas similarity of the two images suggested asplenia. This procedure was useful in establishing asplenia in 4 patients and confirming the presence of a rudimentary or ectopic spleen in 2 others. Unequivocal demonstration of the spleen on the sulfur colloid scans makes the hepatobiliary study unnecessary, while unequivocal demonstration of a normal-appearing liver without splenic activity may warrant a tagged red-cell study for a more complete evaluation.

Lateral cervical meningocele.

Although lateral meningoceles have been described in the thorax, they have not been previously reported in the neck. We describe an infant who was born with a lateral meningocele in the cervical posterior triangle that was felt clinically to be cystic hygroma. Surgical excision was complicated by a cerebral spinal fluid fistula and subsequent meningitis. Problems that this patient presented and potential complications in management are discussed. Although the clinical manifestations of lateral meningoceles and extradural cysts are quite different, there are many anatomic similarities between these entities and other cervical masses that confuse diagnosis and nosology. Their differential diagnosis is reviewed.