Skeletal Dysplasia Involving the Subaxial Cervical Spine
Skeletal Dysplasia Involving the Subaxial Cervical Spine
Because skeletal dysplasias are primary disorders of bone, they have not been commonly understood as neurosurgical diseases. Nevertheless, neurosurgical complications are commonly encountered in many cases of dysplasia syndromes. The authors present two cases of skeletal dysplasia that caused overt instability of the cervical spine. One patient with a diagnosis of Gorham disease of the cervical spine was treated with prolonged fixation in a halo brace after an initial attempt at instrumentation with a posterior occiput-C4 fusion. The other patient, who at birth was identified to have camptomelic dysplasia, has been treated conservatively from the outset. Although these two patients presented with different disorders−in one patient adequate mature bone never formed and in the other patient progressive bone loss became apparent after a seemingly normal initial development−these cases demonstrate unequivocally that surgical options for fusion are ultimately limited by the quality of the underlying bone. In patients in whom the bone itself is inadequate for use as a substrate for fusion, there are currently limited treatment options. Future improvements in our understanding of chondrogenesis and ossification may lead to the design of superior methods of encouraging fusion in these patients; however, at the present time, long-term maintenance in a halo brace may, in fact, be the only treatment.
Skeletal dysplasias are a heterogeneous group of disorders that have in common abnormal bone formation or remodeling (such as ossification or osteolysis). Although many types of dysplasia are quite rare, in aggregate they represent a significant disease burden, especially in the pediatric population. Skeletal dysplasias may be generalized conditions involving the entire skeleton, such as osteochondral dysplasias, or they may be limited to involvement of single bones or malformations of single groups of bones, such as fibrous dysplasia or cleidocranial dysplasia (collectively considered dysostoses). The traditional classification of skeletal dysplasias is dependent on x-ray studies of the skeleton and a description of the abnormality as it relates to the location of the bone. The need for a comprehensive classification of skeletal dysplasias prompted the creation of the "International Nomenclature of Constitutional Diseases of Bones." According to this classification, skeletal dysplasias, of which more than 200 have been described, are categorized into five primary groups: osteochondral dysplasias, dysostoses, idiopathic osteolytic syndromes, primary chromosomal abnormalities, and primary metabolic abnormalities.
In all skeletal dysplasias, the primary pathophysiological process is an abnormality of the underlying bone; neurological morbidity, when it occurs, is secondary to the underlying pathological bone process. Thus skeletal dysplasias have not been commonly understood as neurosurgical diseases. Nevertheless, neurosurgical complications caused by craniocervical junction instability, associated spinal dysraphism, secondary cranial and peripheral neuropathies, and hydrocephalus occur in conjunction with many skeletal dysplasias. Although atlantooccipital instability and thoracic kyphoscoliosis are relatively common findings among the various skeletal dysplasias (specifically the osteochondral dysplasias and metabolic diseases of bone), subaxial instability is less well recognized as a feature of these disease processes. In addition, because by definition the involved bone is an abnormal substrate for fusion, treatment of these patients can be extremely challenging.
We present two cases that represent opposite ends of the spectrum of skeletal dysplasias: an infant presenting with cervical kyphosis due to a congential defect in the development of bone (camptomelic syndrome, an osteochondral dysplasia), and a patient with Gorham disease of the cervical spine (an idiopathic osteolytic disease). Together these patients illustrate clinical challenges in the neurosurgical management of the subaxial spine in children with constitutional diseases of the bone.
Abstract and Introduction
Abstract
Because skeletal dysplasias are primary disorders of bone, they have not been commonly understood as neurosurgical diseases. Nevertheless, neurosurgical complications are commonly encountered in many cases of dysplasia syndromes. The authors present two cases of skeletal dysplasia that caused overt instability of the cervical spine. One patient with a diagnosis of Gorham disease of the cervical spine was treated with prolonged fixation in a halo brace after an initial attempt at instrumentation with a posterior occiput-C4 fusion. The other patient, who at birth was identified to have camptomelic dysplasia, has been treated conservatively from the outset. Although these two patients presented with different disorders−in one patient adequate mature bone never formed and in the other patient progressive bone loss became apparent after a seemingly normal initial development−these cases demonstrate unequivocally that surgical options for fusion are ultimately limited by the quality of the underlying bone. In patients in whom the bone itself is inadequate for use as a substrate for fusion, there are currently limited treatment options. Future improvements in our understanding of chondrogenesis and ossification may lead to the design of superior methods of encouraging fusion in these patients; however, at the present time, long-term maintenance in a halo brace may, in fact, be the only treatment.
Introduction
Skeletal dysplasias are a heterogeneous group of disorders that have in common abnormal bone formation or remodeling (such as ossification or osteolysis). Although many types of dysplasia are quite rare, in aggregate they represent a significant disease burden, especially in the pediatric population. Skeletal dysplasias may be generalized conditions involving the entire skeleton, such as osteochondral dysplasias, or they may be limited to involvement of single bones or malformations of single groups of bones, such as fibrous dysplasia or cleidocranial dysplasia (collectively considered dysostoses). The traditional classification of skeletal dysplasias is dependent on x-ray studies of the skeleton and a description of the abnormality as it relates to the location of the bone. The need for a comprehensive classification of skeletal dysplasias prompted the creation of the "International Nomenclature of Constitutional Diseases of Bones." According to this classification, skeletal dysplasias, of which more than 200 have been described, are categorized into five primary groups: osteochondral dysplasias, dysostoses, idiopathic osteolytic syndromes, primary chromosomal abnormalities, and primary metabolic abnormalities.
In all skeletal dysplasias, the primary pathophysiological process is an abnormality of the underlying bone; neurological morbidity, when it occurs, is secondary to the underlying pathological bone process. Thus skeletal dysplasias have not been commonly understood as neurosurgical diseases. Nevertheless, neurosurgical complications caused by craniocervical junction instability, associated spinal dysraphism, secondary cranial and peripheral neuropathies, and hydrocephalus occur in conjunction with many skeletal dysplasias. Although atlantooccipital instability and thoracic kyphoscoliosis are relatively common findings among the various skeletal dysplasias (specifically the osteochondral dysplasias and metabolic diseases of bone), subaxial instability is less well recognized as a feature of these disease processes. In addition, because by definition the involved bone is an abnormal substrate for fusion, treatment of these patients can be extremely challenging.
We present two cases that represent opposite ends of the spectrum of skeletal dysplasias: an infant presenting with cervical kyphosis due to a congential defect in the development of bone (camptomelic syndrome, an osteochondral dysplasia), and a patient with Gorham disease of the cervical spine (an idiopathic osteolytic disease). Together these patients illustrate clinical challenges in the neurosurgical management of the subaxial spine in children with constitutional diseases of the bone.
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