Sclerostin is a delayed secreted product of osteocytes that inhibits bone formation

Osteocytes are the most abundant cells in bone and are ideally located to influence bone turnover through their syncytial relationship with surface bone cells. Osteocyte-derived signals have remained largely enigmatic, but it was recently reported that human osteocytes secrete sclerostin, an inhibitor of bone formation. Absent sclerostin protein results in the high bone mass clinical disorder sclerosteosis. Here we report that within adult iliac bone, newly embedded osteocytes were negative for sclerostin staining but became positive at or after primary mineralization. The majority of mature osteocytes in mineralized cortical and cancellous bone was positive for sclerostin with diffuse staining along dendrites in the osteocyte canaliculi. These findings provide for the first time in vivo evidence to support the concept that osteocytes secrete sclerostin after they become embedded in a mineralized matrix to limit further bone formation by osteoblasts. Sclerostin did not appear to influence the formation of osteocytes. We propose that sclerostin production by osteocytes may regulate the linear extent of formation and the induction or maintenance of a lining cell phenotype on bone surfaces. In doing so, sclerostin may act as a key inhibitory signal governing skeletal microarchitecture.

Skeletal overgrowth and deafness in mice lacking fibroblast growth factor receptor 3

Fibroblast growth factor receptor 3 (Fgfr3) is a tyrosine kinase receptor expressed in developing bone, cochlea, brain and spinal cord. Achondroplasia, the most common genetic form of dwarfism, is caused by mutations in FGFR3. Here we show that mice homozygous for a targeted disruption of Fgfr3 exhibit skeletal and inner ear defects. Skeletal defects include kyphosis, scoliosis, crooked tails and curvature and overgrowth of long bones and vertebrae. Contrasts between the skeletal phenotype and achondroplasia suggest that activation of FGFR3 causes achondroplasia. Inner ear defects include failure of pillar cell differentiation and tunnel of Corti formation and result in profound deafness. Our results demonstrate that Fgfr3 is essential for normal endochondral ossification and inner ear development.

The PERK eukaryotic initiation factor 2 alpha kinase is required for the development of the skeletal system, postnatal growth, and the function and viability of the pancreas

Phosphorylation of eukaryotic initiation factor 2 alpha (eIF-2 alpha) is typically associated with stress responses and causes a reduction in protein synthesis. However, we found high phosphorylated eIF-2 alpha (eIF-2 alpha[P]) levels in nonstressed pancreata of mice. Administration of glucose stimulated a rapid dephosphorylation of eIF-2 alpha. Among the four eIF-2 alpha kinases present in mammals, PERK is most highly expressed in the pancreas, suggesting that it may be responsible for the high eIF-2 alpha[P] levels found therein. We describe a Perk knockout mutation in mice. Pancreata of Perk(-/-) mice are morphologically and functionally normal at birth, but the islets of Langerhans progressively degenerate, resulting in loss of insulin-secreting beta cells and development of diabetes mellitus, followed later by loss of glucagon-secreting alpha cells. The exocrine pancreas exhibits a reduction in the synthesis of several major digestive enzymes and succumbs to massive apoptosis after the fourth postnatal week. Perk(-/-) mice also exhibit skeletal dysplasias at birth and postnatal growth retardation. Skeletal defects include deficient mineralization, osteoporosis, and abnormal compact bone development. The skeletal and pancreatic defects are associated with defects in the rough endoplasmic reticulum of the major secretory cells that comprise the skeletal system and pancreas. The skeletal, pancreatic, and growth defects are similar to those seen in human Wolcott-Rallison syndrome.

Achondroplasia: a comprehensive clinical review

Achondroplasia is the most common of the skeletal dysplasias that result in marked short stature (dwarfism). Although its clinical and radiologic phenotype has been described for more than 50 years, there is still a great deal to be learned about the medical issues that arise secondary to this diagnosis, the manner in which these are best diagnosed and addressed, and whether preventive strategies can ameliorate the problems that can compromise the health and well being of affected individuals. This review provides both an updated discussion of the care needs of those with achondroplasia and an exploration of the limits of evidence that is available regarding care recommendations, controversies that are currently present, and the many areas of ignorance that remain.

Assessment of early osteoarthritis in hip dysplasia with delayed gadolinium-enhanced magnetic resonance imaging of cartilage

BACKGROUND

The efficacy of surgical and medical treatment of osteoarthritis is difficult to assess because of the lack of a noninvasive, sensitive measure of cartilage integrity. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) was designed to specifically examine glycosaminoglycan changes in articular cartilage that occur during the development of osteoarthritis. Our primary goal was to compare this technique with measurement of the joint space width on conventional radiographs in patients with hip dysplasia. We performed this comparison by assessing the correlation between the findings of each technique and clinically important factors such as pain, severity of dysplasia, and age.

METHODS

Sixty-eight hips in forty-three patients were included in the study. Clinical symptoms were assessed with use of the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) questionnaire. The width of the joint space as well as the lateral center-edge angle of Wiberg (as a measure of the severity of the dysplasia) was measured on standard standing radiographs. Magnetic resonance imaging maps of glycosaminoglycan distribution were made with T1-calculated images after administration of gadopentetate (2-) (Gd-DTPA (2-) ). The dGEMRIC index was calculated as the average of the T1 values for the acetabular and femoral head cartilages.

RESULTS

The dGEMRIC index correlated with both pain (rs = -0.50, p < 0.0001) and the lateral center-edge angle (rs = 0.52, p < 0.0001), whereas the joint space width did not correlate with either, with the numbers available. There was a correlation between the dGEMRIC index and pain whether or not a labral tear was present. The dGEMRIC index was significantly different (p < 0.0001) among three groups of hips classified according to whether they had mild, moderate, or severe dysplasia, whereas the joint space width did not differ significantly among these three groups. There was no significant correlation between age and any of the other parameters.

CONCLUSIONS

We demonstrated that, in patients with hip dysplasia, the dGEMRIC index-a measure of the biochemical integrity of cartilage-correlates with pain and the severity of the dysplasia and is significantly different among groups of hips with mild, moderate, and severe dysplasia, suggesting that it may be a sensitive measure of early osteoarthritis. Additional studies are needed to determine whether dGEMRIC can be used to predict disease progression in different situations and/or demonstrate responses to therapeutic interventions.

Tartrate-resistant acid phosphatase deficiency causes a bone dysplasia with autoimmunity and a type I interferon expression signature

We studied ten individuals from eight families showing features consistent with the immuno-osseous dysplasia spondyloenchondrodysplasia. Of particular note was the diverse spectrum of autoimmune phenotypes observed in these individuals (cases), including systemic lupus erythematosus, Sjögren's syndrome, hemolytic anemia, thrombocytopenia, hypothyroidism, inflammatory myositis, Raynaud's disease and vitiligo. Haplotype data indicated the disease gene to be on chromosome 19p13, and linkage analysis yielded a combined multipoint log(10) odds (LOD) score of 3.6. Sequencing of ACP5, encoding tartrate-resistant acid phosphatase, identified biallelic mutations in each of the cases studied, and in vivo testing confirmed a loss of expressed protein. All eight cases assayed showed elevated serum interferon alpha activity, and gene expression profiling in whole blood defined a type I interferon signature. Our findings reveal a previously unrecognized link between tartrate-resistant acid phosphatase activity and interferon metabolism and highlight the importance of type I interferon in the genesis of autoimmunity.

ATF4 mediation of NF1 functions in osteoblast reveals a nutritional basis for congenital skeletal dysplasiae

The transcription factor ATF4 enhances bone formation by favoring amino acid import and collagen synthesis in osteoblasts, a function requiring its phosphorylation by RSK2, the kinase inactivated in Coffin-Lowry Syndrome. Here, we show that in contrast, RSK2 activity, ATF4-dependent collagen synthesis, and bone formation are increased in mice lacking neurofibromin in osteoblasts (Nf1(ob)(-/-) mice). Independently of RSK2, ATF4 phosphorylation by PKA is enhanced in Nf1(ob)(-/-) mice, thereby increasing Rankl expression, osteoclast differentiation, and bone resorption. In agreement with ATF4 function in amino acid transport, a low-protein diet decreased bone protein synthesis and normalized bone formation and bone mass in Nf1(ob)(-/-) mice without affecting other organ weight, while a high-protein diet overcame Atf4(-/-) and Rsk2(-/-) mice developmental defects, perinatal lethality, and low bone mass. By showing that ATF4-dependent skeletal dysplasiae are treatable by dietary manipulations, this study reveals a molecular connection between nutrition and skeletal development.

Impaired gastric acidification negatively affects calcium homeostasis and bone mass

Activation of osteoclasts and their acidification-dependent resorption of bone is thought to maintain proper serum calcium levels. Here we show that osteoclast dysfunction alone does not generally affect calcium homeostasis. Indeed, mice deficient in Src, encoding a tyrosine kinase critical for osteoclast activity, show signs of osteopetrosis, but without hypocalcemia or defects in bone mineralization. Mice deficient in Cckbr, encoding a gastrin receptor that affects acid secretion by parietal cells, have the expected defects in gastric acidification but also secondary hyperparathyroidism and osteoporosis and modest hypocalcemia. These results suggest that alterations in calcium homeostasis can be driven by defects in gastric acidification, especially given that calcium gluconate supplementation fully rescues the phenotype of the Cckbr-mutant mice. Finally, mice deficient in Tcirg1, encoding a subunit of the vacuolar proton pump specifically expressed in both osteoclasts and parietal cells, show hypocalcemia and osteopetrorickets. Although neither Src- nor Cckbr-deficient mice have this latter phenotype, the combined deficiency of both genes results in osteopetrorickets. Thus, we find that osteopetrosis and osteopetrorickets are distinct phenotypes, depending on the site or sites of defective acidification.

Delayed gadolinium-enhanced magnetic resonance imaging of cartilage to predict early failure of Bernese periacetabular osteotomy for hip dysplasia

BACKGROUND

Hip dysplasia leads to abnormal loading of articular cartilage, which results in osteoarthritis. Pelvic osteotomies such as the Bernese periacetabular osteotomy can improve the mechanics of the joint, but the results are variable and appear to depend on the amount of preexisting arthritis. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) is a technique designed to measure early arthritis, and it potentially could be used to select hips with too severe arthritis to benefit from a joint-preserving reconstructive procedure. The purpose of our study was to identify radiographic, clinical, and magnetic resonance imaging measurements that predict failure after pelvic osteotomy.

METHODS

We performed a cohort study of forty-seven patients undergoing a Bernese periacetabular osteotomy for the treatment of hip dysplasia. Our goal was to identify preoperative radiographic factors, such as the grade of arthritis, joint congruency, and the dGEMRIC index, that are associated with a poor outcome after osteotomy.

RESULTS

Hips in which the osteotomy did not fail had a significant decrease in pain compared with their status preoperatively (p < 0.0001). Hips in which the osteotomy did fail had had significantly more arthritis on preoperative radiographs (as demonstrated by the joint space width and the Tönnis grade [p = 0.01]), more subluxation (p = 0.02), and a lower dGEMRIC index (p < 0.001) than the hips in which the osteotomy did not fail. Multivariate analysis identified the dGEMRIC index as the most important predictor of failure of the osteotomy.

CONCLUSIONS

Bernese periacetabular osteotomy for the treatment of hip dysplasia can decrease pain and improve function in symptomatic dysplastic hips. The dGEMRIC index, as an early measure of osteoarthritis, appears to be useful for identifying poor candidates for a pelvic osteotomy.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

The tandem CCCH zinc finger protein tristetraprolin and its relevance to cytokine mRNA turnover and arthritis

Tristetraprolin (TTP) is the best-studied member of a small family of three proteins in humans that is characterized by a tandem CCCH zinc finger (TZF) domain with highly conserved sequences and spacing. Although initially discovered as a gene that could be induced rapidly and transiently by the stimulation of fibroblasts with growth factors and mitogens, it is now known that TTP can bind to AU-rich elements in mRNA, leading to the removal of the poly(A) tail from that mRNA and increased rates of mRNA turnover. This activity was discovered after TTP-deficient mice were created and found to have a systemic inflammatory syndrome with severe polyarticular arthritis and autoimmunity, as well as medullary and extramedullary myeloid hyperplasia. The syndrome seemed to be due predominantly to excess circulating tumor necrosis factor-α (TNF-α), resulting from the increased stability of the TNF-α mRNA and subsequent higher rates of secretion of the cytokine. The myeloid hyperplasia might be due in part to increased stability of granulocyte–macrophage colony-stimulating factor (GM-CSF). This review highlights briefly the characteristics of the TTP-deficiency syndrome in mice and its possible genetic modifiers, as well as recent data on the characteristics of the TTP-binding site in the TNF-α and GM-CSF mRNAs. Recent structural data on the characteristics of the complex between RNA and one of the TTP-related proteins are reviewed, and used to model the TTP-RNA binding complex. We review the current knowledge of TTP sequence variants in humans and discuss the possible contributions of the TTP-related proteins in mouse physiology and in human monocytes. The TTP pathway of TNF-α and GM-CSF mRNA degradation is a possible novel target for anti-TNF-α therapies for rheumatoid arthritis, and also for other conditions proven to respond to anti-TNF-α therapy.

Wild-type and brachyolmia-causing mutant TRPV4 channels respond directly to stretch force

Whether animal ion channels functioning as mechanosensors are directly activated by stretch force or indirectly by ligands produced by the stretch is a crucial question. TRPV4, a key molecular model, can be activated by hypotonicity, but the mechanism of activation is unclear. One model has this channel being activated by a downstream product of phospholipase A(2), relegating mechanosensitivity to the enzymes or their regulators. We expressed rat TRPV4 in Xenopus oocytes and repeatedly examined >200 excised patches bathed in a simple buffer. We found that TRPV4 can be activated by tens of mm Hg pipette suctions with open probability rising with suction even in the presence of relevant enzyme inhibitors. Mechanosensitivity of TRPV4 provides the simplest explanation of its various force-related physiological roles, one of which is in the sensing of weight load during bone development. Gain-of-function mutants cause heritable skeletal dysplasias in human. We therefore examined the brachyolmia-causing R616Q gain-of-function channel and found increased whole-cell current densities compared with wild-type channels. Single-channel analysis revealed that R616Q channels maintain mechanosensitivity but have greater constitutive activity and no change in unitary conductance or rectification.

Majewski osteodysplastic primordial dwarfism type II (MOPD II): natural history and clinical findings

A description of the clinical features of Majewski osteodysplastic primordial dwarfism type II (MOPD II) is presented based on 58 affected individuals (27 from the literature and 31 previously unreported cases). The remarkable features of MOPD II are: severe intrauterine growth retardation (IUGR), severe postnatal growth retardation; relatively proportionate head size at birth which progresses to true and disproportionate microcephaly; progressive disproportion of the short stature secondary to shortening of the distal and middle segments of the limbs; a progressive bony dysplasia with metaphyseal changes in the limbs; epiphyseal delay; progressive loose-jointedness with occasional dislocation or subluxation of the knees, radial heads, and hips; unusual facial features including a prominent nose, eyes which appear prominent in infancy and early childhood, ears which are proportionate, mildly dysplastic and usually missing the lobule; a high squeaky voice; abnormally, small, and often dysplastic or missing dentition; a pleasant, outgoing, sociable personality; and autosomal recessive inheritance. Far-sightedness, scoliosis, unusual pigmentation, and truncal obesity often develop with time. Some individuals seem to have increased susceptibility to infections. A number of affected individuals have developed dilation of the CNS arteries variously described as aneurysms and Moya Moya disease. These vascular changes can be life threatening, even in early years because of rupture, CNS hemorrhage, and strokes. There is variability between affected individuals even within the same family.

Sclerosing bone dysplasias--a target-site approach

Sclerosing bone dysplasias are a poorly understood group of developmental anomalies, much of whose etiology is still obscure. The list of conditions constituting this group is relatively short: osteopetrosis (Albers-Schönberg disease), pycnodysostosis (Maroteaux-Lamy disease), enostosis (bone island), osteopoikilosis, osteopathia striata (Voorhoeve disease), progressive diaphyseal dysplasia (Camurati-Engelmann disease), hereditary multiple diaphyseal sclerosis (Ribbing disease), four types of endosteal hyperostosis (van Buchem disease, Worth disease, Nakamura disease, and Truswell-Hansen disease), dysosteosclerosis, metaphyseal dysplasia (Pyle's disease), craniometaphyseal dysplasia, melorheostosis (Leri disease), and craniodiaphyseal dysplasia. There are instances in which two or more of the above disorders coexist. These are termed "overlap syndromes", most commonly involving osteopathia striata, osteopoikilosis, and melorheostosis. A classification of these dysplasias is elaborated based on a targetsite approach that views them as disturbances in development associated with the processes of either endochondral or intramembranous bone formation, or both. Accumulated evidence suggests that many of these disorders stem from common defects in bone resorption and/or formation during the processes of skeletal maturation and modeling. Finally, the subgroup of overlap syndromes is emphasized as indicating a strong interrelationship between the sclerosing dysplasias of bone, with perhaps a common pathogenesis for many.

A new chondrodystrophic mutant in mice. Electron microscopy of normal and abnormal chondrogenesis

The occurrence of a new mutation affecting cartilage and bone in mice is reported. The gene is lethal, shows autosomal recessive inheritance, and has high penetrance. It is not allelic to shorthead and probably not to phocomelia or achondroplasia. It results in a foreshortened face, cleft palate, defective trachea, and shortened long bones with flared metaphyses. Chondrocytes of epiphyseal cartilage from the mutant are not aligned in columns, and there is a decrease in the usual staining of the cartilage matrix. Electron microscope observations show large, wide collagen fibrils with "native" banding in the matrix of mutant cartilage, which are not present in normal cartilage. Possible explanations for the expression of this genetic disorder of cartilage development are put forward.

Distinguishing features of focal cemento-osseous dysplasia and cemento-ossifying fibromas. II. A clinical and radiologic spectrum of 316 cases

The distinguishing histopathologic features of focal cemento-osseous dysplasia (FCOD) (including lesions occurring in both anterior and posterior jaws) and cemento-ossifying fibroma (COF) (ossifying fibroma and cementifying fibroma) were demonstrated in our earlier work. The aim of the current study was to further refine their clinical and radiographic features. We have assessed 18 clinical and radiographic parameters by univariate comparisons (chi-squared and Student t tests), and a multivariate assessment (logistic regression) in 241 cases of FCOD and 75 of COF. These cases were diagnosed from a combination of clinical, radiographic, and histopathologic information. FCOD was seen predominantly in black women, with a peak incidence in the fourth and fifth decades, whereas COF showed no female predilection except in the fourth decade (p < 0.005). COF occurred in patients an average of 10 years younger than patients with FCOD (p < 0.0001). Most patients with FCOD were asymptomatic (62%); the average lesion size was 1.8 cm. More than half of patients with COF displayed jaw expansion and a considerably larger size lesion (mean 3.8 cm, p < 0.001). The mandible was the most frequent site for both FCOD (86%) and COF (70%). Radiographically, a well-defined border was observed in 53% of cases of FCOD and 85% of cases of COF (p < 0.01). Cases of FCOD mostly demonstrated an irregularly mixed radio-opacity (69%), whereas 53% of COFs presented as a radiolucency (p < 0.005). In FCOD, there was a close association with tooth apices (70.6%, p < 0.0001) or with previous extraction sites (21%, p < 0.05); however, the majority of COF cases (86%) showed no relationship with either. Combining the radiographic feature of a periapical location with the pathology of multiple curetted fragments and "ginger root" bony trabeculae, allowed 90% sensitivity and 89% specificity in a logistic regression model to predict the lesion to be an FCOD. These findings provide guidelines not only to distinguish these two entities clinically, but also aid in reaching an accurate diagnosis histopathologically.

The patella morphology in trochlear dysplasia--a comparative MRI study

BACKGROUND

Trochlear dysplasia is suspected to have a genetic basis and causes recurrent patellar instability due to insufficient anatomical geometry. Numerous studies about trochlear morphology and the optimal surgical treatment have been carried out, but no attention has been paid to the corresponding patellar morphology.

PURPOSE

The aim of this study was the evaluation of the patellar morphology in normal and trochlear dysplastic knees.

STUDY DESIGN

Biometric analysis.

METHODS

Twenty two patellae with underlying trochlear dysplasia (study group--SG) were compared with 22 matched knees with normal trochlear shape (control group--CG) on transverse and sagittal MRI slices. We compared transverse diameter, cartilaginous thickness, Wiberg-index and -angle, length and radius of lateral and medial facet, patellar shape and angle, retropatellar length, and type of trochlear dysplasia. For statistical analysis we used the Wilcoxon signed ranks test.

RESULTS

The transverse and sagittal diameter, mean length of medial patellar facet, and mean cartilaginous and subchondral Wiberg-index showed statistical differences between the two groups.

CONCLUSIONS

Although the insufficient trochlear depth and decreased lateral trochlear slope are responsible for patellofemoral instability, the patella shows morphological changes in trochlear dysplastic knees. Its overall size and the medial facet are smaller. Although the femoral sulcus angle is larger, the Wiberg-angle and -index are equal to the control group. This may indicate that the patellar morphology may not be a result of missing medial patellofemoral pressure in trochlear dysplastic knees, but a decreased medial patellofemoral traction. This seems to be caused by hypotrophic medial patellofemoral restraints in combination with an increased lateral patellar tilt, both resulting in a decreased tension onto the medial patella facet. Whether there is a genetic component to the patellar morphology remains open.

Cartilage-bone mismatch in the dysplastic trochlea. An MRI study

Trochlear dysplasia is an important anatomical abnormality in symptomatic patellar instability. Our study assessed the mismatch between the bony and cartilaginous morphology in patients with a dysplastic trochlea compared with a control group. MRI scans of 25 knees in 23 patients with trochlear dysplasia and in 11 patients in a randomly selected control group were reviewed retrospectively in order to assess the morphology of the cartilaginous and bony trochlea. Inter- and intra-observer error was assessed. In the dysplastic group there were 15 women and eight men with a mean age of 20.4 years (14 to 30). The mean bony sulcus angle was 167.9 degrees (141 degrees to 203 degrees), whereas the mean cartilaginous sulcus angle was 186.5 degrees (152 degrees to 214 degrees; p < 0.001). In 74 of 75 axial images (98.7%) the cartilaginous contour was different from the osseous contour on subjective assessment, the cartilage exacerbated the abnormality. Our study shows that the morphology of the cartilaginous trochlea differs markedly from that of the underlying bony trochlea in patients with trochlear dysplasia. MRI is necessary in order to demonstrate the pathology and to facilitate surgical planning.

Distinguishing features of focal cemento-osseous dysplasias and cemento-ossifying fibromas: I. A pathologic spectrum of 316 cases

Focally expressed cemento-osseous dysplasia (periapical cemento-osseous dysplasia and focal cemento-osseous dysplasia) and cemento-ossifying fibroma (ossifying fibroma and cementifying fibroma) are two clinically recognized entities that are not easily differentiated histopathologically because of the lack of recognition of specific microscopic features. We have assessed 20 pathologic parameters for their ability to distinguish reliably between the two. Included in this study were 241 cases of focally expressed cemento-osseous dysplasia and 75 cases of cemento-osseous fibroma diagnosed from a combination of clinical, radiographic, and histopathologic information. Results revealed that 92.5% of focally expressed cemento-osseous dysplasia were composed of multiple small fragments of tissue whereas 88.0% of cemento-osseous fibromas showed a large intact specimen. Thick curvilinear trabeculae ("ginger root" pattern) or irregularly shaped cementum-like masses were typically seen in focally expressed cemento-osseous dysplasia, whereas thin isolated trabeculae with prominent osteoblastic rimming were more commonly observed in cemento-osseous fibroma. The stroma of focally expressed cemento-osseous dysplasia often displayed characteristic cavernous-like vascularity that was almost always associated with bony trabeculae. Free hemorrhage was frequently interspersed in the artifactual spaces throughout focally expressed cemento-osseous dysplasia. In contrast, the cases of cemento-osseous fibroma showed more cellularity in the stroma in which a storiform pattern was present in more than half the lesions studied. Giant cells, when present in cemento-osseous fibroma, were clustered in the center of the cellular stroma. The features described here allowed distinction histopathologically in 94% of cases studied. Three progressive stages of focally expressed cemento-osseous dysplasia and subtypes of cemento-osseous fibroma may be recognizable microscopically.

Sclerosing bone dysplasias: genetic and radioclinical features

Although knowledge of basic genetics in the field of sclerosing bone dysplasias is progressing, the radiologist still plays a pivotal role in the diagnosis of this relatively poorly understood group of disorders. Based on a target site approach, these anomalies are classified into three groups. Within each group, further differentiation can be made by distinctive clinical findings and by mode of inheritance: (a) dysplasias of endochondral bone formation: osteopetrosis (Albers-Schönberg disease), pycnodysostosis, enostosis, osteopoikilosis, osteopathia striata (Voorhoeve disease); (b) dysplasias of intramembranous bone formation: progressive diaphyseal dysplasia (Camurati-Engelmann disease) and variants, hyperostosis corticalis generalisata (Van Buchem disease) and variants; and (c) mixed sclerosing dysplasias: melorheostosis (Leri disease) and overlap syndromes.

Asphyxiating thoracic dysplasia. Clinical, radiological, and pathological information on 10 patients

Review of 10 cases of asphyxiating thoracic dysplasia has shown a wide range of clinical effects and some variability in the radiographic features. Respiratory difficulty was severe in 7 babies and lethal in 6 of these. The seventh child is remarkable for his normal stature and excellent health at 15 years of age. 3 babies had no respiratory difficulty but 2 of them subsequently died of renal failure; one remains alive at 3 years. Microscopical abnormalities in the liver and kidneys were very frequent and appeared to increase progressively with age.

The chondro-osseous dysplasia of adenosine deaminase deficiency with severe combined immunodeficiency

Three children, two of them siblings, with severe combined immunodeficiency and adenosine deaminase deficiency died within the first six months of life from the complications of acute bacterial infections. Subtle radiographic abnormalities were seen at the costochondral junctions, at the apophysis of the iliac bones, and in the vertebral bodies. At autopsy, the thymus showed evidence of early differentiation and, in one instance, aborted Hassall's corpuscles. Histologic study of the bone disclosed lack of organized cartilage columnar formation, large lacuni containing hypertrophied cells, and lack of trabecular formation with uninterrupted areas of calcified cartilage. These changes are distinctly different from those observed in the metaphyseal chondrodysplasias or in other chondrodystrophies.

A case of lethal congenital dwarfism with accelerated skeletal maturation

Details of a female infant, who was born after 29 weeks gestation and who died within minutes of birth, are presented. The infant was hydropic, showed macroglossia and had very short limbs with normal sized hands and feet. Apart from a preductal aortic coarctation the pathological findings were confined to the skeleton. The radiographical and histological findings are described in detail; they differ from those of previous studies of similar conditions.

Radiographic characteristics of lower-extremity bowing in children

Lower-extremity bowing is common in infants and children and can result from a variety of conditions. At radiography, developmental bowing shows varus angulation centered at the knee, "metaphyseal beaking," thickening of the medial tibial cortices, and tilted ankle joints. Tibia vara (Blount disease) demonstrates genu varum and depression of the proximal tibia medially. Congenital bowing manifests as posteromedial bowing with cortical thickening along the concavity of the curvature and, in some cases, diaphyseal broadening. In rickets, radiographic changes occur primarily at sites of rapid growth and are predominantly metaphyseal, with widening of the zone of provisional calcification. Achondroplasia is characterized by shortening and thickening of the long bones with metaphyseal flaring and cupping. In neurofibromatosis, there may be anterolateral bowing of the tibia, and there is often focal narrowing and intramedullary sclerosis or cystic change at the apex of the angulation. The tibia is typically involved at the junction of the middle and distal thirds. Osteogenesis imperfecta demonstrates bowing from softening due to osteoporosis and multiple fractures and typically involves the entire skeleton. In camptomelic dysplasia, lower-extremity bowing is associated with a short trunk, short limbs, and deficiencies in pelvic bone development. Recognition of these pathologic conditions is important for differentiating those that will resolve spontaneously from those that require surgery or other treatment.

Computed tomography and/or magnetic resonance imaging before pediatric cochlear implantation? Developing an investigative strategy

OBJECTIVE

To investigate and compare the usefulness of preoperative magnetic resonance (MR) imaging and high-resolution temporal bone computed tomography (HRCT) in pediatric cochlear implant candidates.

STUDY DESIGN

Prospective.

SETTING

Tertiary referral center.

PATIENTS

A cohort of 92 pediatric patients with profound hearing. Inclusion criteria were MR, computed tomography, and cochlear implantation. INTERVENTION.

DIAGNOSTIC

All patients had preoperative imaging of the petrous temporal bone (HRCT, T2-weighted fast spin echo, axial 3D Fast Imaging Employing Steady-state Acquisition [FIESTA] MR) and brain (Fast Fluid-attenuated Inversion-recovery [FLAIR] MR).

MAIN OUTCOME MEASURE(S)

Overall prevalence of inner ear dysplasias in this population and comparison of detection rates between HRCT, T2 Fast Spin Echo (FSE), and FIESTA MR sequences.

RESULTS

Radiological abnormalities were observed in 32 and 59% of MR and HRCT temporal bone, respectively. Synchronous intracranial findings were noted in 40% on brain MR. Common vestibulocochlear nerve was observed in 3% ears and directed side of implantation. Consistent discrepancies noted on HRCT were inability to diagnose early obliterative labyrinthitis and presence of the cochlear nerve in the internal auditory canal. With respect to MR, enlarged vestibular aqueducts and narrow cochlear nerve canals were consistently under identified.

CONCLUSION

Dual-modality imaging with HRCT and MR of petrous bone and MR brain in the precochlear implant pediatric population detects abnormalities related to deafness, which would not otherwise be found using either modality alone. There is overlap between the imaging modalities in the type of abnormalities detected, and we present a case for selective use of HRCT within a diagnostic algorithm, using the patient risk factors we have identified.