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Imaging of the cranium: Pictorial essay
Imaging of the Cranium: Pictorial Essay 1 Thu T. Tang, MD, Michael S. McLeary, MD
The calvaria and its contours can be distorted by a number of diseases. Often the involvement is so characteristic that the pathologic diagnosis can be suggested simply from the cranial imaging. Occasionally the skull is deformed secondarily, reflecting only the status of the brain or meninges. In either case the radiologist is the primary person able to detect the abnormality, assess its importance, and suggest further definitive testing. In this pictorial essay, we will demonstrate 22 different entities that involve the cranium. The primary imaging modalities will be conventional radiography, axial and three-dimensional computed tomography (CT), magnetic resonance (MR) imaging, and ultrasound (US) imaging.
Anencephaly is the most common congenital malformation of the brain. The calvarial vault is absent above the orbit, and the cerebral hemispheres are replaced by malformed brain or angiodysplastic tissue (1). When this condition is diagnosed in utero, US shows no echogenic evidence of an overlying calvaria. Large tufts of moderately echogenic tissue extending superiorly from the top of the head, consistent with the appearance of angiodysplastic tissue, are often seen (Fig 1) (2).
Acad Radio11999; 6:132-140
1From the Division of Pediatric Radiology, Loma Linda University Children's Hospital, 11234 AndersonSt, Loma Linda, CA 92354. ReceivedMarch 16, 1998; revision requested March 19; revision received June 19; accepted
August 19. Address reprint requests to M.S.M. ©AUR, 1999
132
Figure 1. Anencephaly. Lateral plain radiograph of a stillborn neonate shows that the calvaria is absent and the basal bones of the skull are thickened. The orbits are shallow, and the eyes are protuber-
ant.
Craniosynostosis or premature closure of one or more sutures results in distortion of the calvarial configuration. Craniosynostosis is classified as a primary, isolated event of unknown etiology or as secondary to other disease processes, such as rickets and hypophosphatasia (3). It results in a decrease in the skull diameter perpendicular to the closed suture or sutures and compensatory growth in the remaining sutures, causing characteristic skull deformities (4). Dolichocephaly (premature closure of the sagittal suture) accounts for 50% of all cases of craniosynostosis and an increased anteroposterior and decreased biparietal diameter (Fig 2). Brachycephaly (premature bilateral closure of the coronal or lambdoid sutures or
Vol 6, No 2, February 1999
Figure2. Dolichocephaly. Three-dimensional CT scan of the skull of a 5-month-old male infant demonstrates mild elongation of the skull, with open coronal and lambdoidal sutures and fusion of the sagittal suture. The calvaria is elongated ventrodorsally, and the coronal suture is mildly widened.
IMAGING OF THE CRANIUM
Figure4. Plagiocephaly. Three-dimensionaICT scan of the skull of a 3-month-old female infant shows premature fusion of the right coronal suture and mild asymmetry to the orbits and skull.
in expansion of the greater wings of the sphenoid and elevation of the lesser wings, giving a "harlequin" appearance to the orbits (4). The orbits are often shallow, with maxillary hypoplasia (3). Plagiocephaly (unilateral premature closure of the coronal or lambdoid sutures or both) results in asymmetric deformity of the skull (Fig 4). Trigonocephaly results from fusion of the metopic suture in utero, causing a decrease in the transverse dimension of the anterior cranium. The forehead is triangular in shape, and the interorbital distance is decreased (Fig 5). Kleeblattsch~del or "cloverleaf' skull is the result of premature fusion of all the cranial sutures. It is often accompanied by facial dysmorphism, hypotelorism, hydrocephalus, and mental retardation. Radiographic studies show the classical trilobed configuration of the skull with increased convolutional markings (Fig 6) (4). Figure3. Brachycephaly. Three-dimensional CT scan of the skull of a 3-month-old female infant shows a shallow anterior cranial fossa, with bilateral fused coronal sutures and marked diastasis of the sagittal suture. Additional views (not shown) showed a decrease in the anteroposterior diameter of the skull and an apparent increase in the craniocaudal dimension of the skull.
both) results in a decreased anteroposterior diameter of the skull (Fig 3). In bilateral coronal craniosynostosis, the compensatory growth in the transverse dimension results
Permanent calvarial markings can be secondary to liickensch~idel, increased intracranial pressure, or a normal growth spurt. Lacunar skull, or liickensch~idel, is a bone dysplasia of the calvaria that is present at birth and usually disappears by 4-6 months of age. It is not related to hydrocephalus and is almost always associated with meningocele or encephalomeningocele and an ArnoldChiari type 2 malformation (2,4). Plain skull radiographs
133
Figure 5. Trigonocephaly. Three-dimensional CT scan of the skull of a 5-month-old female infant demonstrates hypotelodsm and prominent ridging of the fused metopic suture.
Figure 6. Kleeblattsch&del. Axial CT scan of the skull of a 24-day-old male infant shows calvarial scalloping and bulging of the temporal bones, causing a trilobed (cloverleaf) appearance.
show a characteristic "soap bubble" appearance, usually involving the parietal and occipital bones (Fig 7) (4). Increased intracranial pressure in a child may be accompanied by calvarial changes. The cranial vault may be enlarged, and the sutures, including the fontanelle, may be diastatic on plain radiographs of the skull. In addition, there may be enlargement and deformity of the sella and an increase in the convolutional markings of the calvaria. CT imaging is helpful in showing early changes, such as subtle spreading of the sutures and mild ventriculomegaly. Late findings are obvious on axial CT
134
Figure 7. L0ckensch&del. Lateral skull radiograph of a 4-month-old female infant with Chiari malformation in whom a spinal myelomeningocele had been repaired at birth shows a scalloped appearance throughout the skull, most prominent in the parieto-occipital regions.
Figure 8. Hydrocephalus. Lateral skull radiograph of a 23-month-old girl with hydrocephalus secondary to shunt malfunction demonstrates widening of the coronal and lambdoidal sutures and slight enlargement of the sella turcica. No convolutional markings are seen.
images, which show severe ventricular dilatation (Fig 8) (2). DIFFUSE SKULL THICKENING In fetal life, hematopoiesis occurs throughout the reticuloendothelial system. Shortly after birth, however, the terminal differentiation of blood precursors resides
Vol 6, No 2, February 1999
IMAGING OF THE CRANIUM
Figure 9. Thalassemia. Lateral skull radiograph demonstrates a widened spiculated calvaria, the "hairon-end" appearance to the skull, secondary to expansion of the marrow space.
Figure 10. Cleidocranial dysplasia. Lateral skull radiograph of an 18-year-old man shows thickening of the frontal bone and multiple wormian bones in the larnbdoidal suture. Note that the permanent teeth have failed to erupt.
predominantly in the marrow cavities of the axial skeleton and the skull. The diploic space is highly expandable when the demand for blood cell production is increased, as it is in patients with chronic hemolytic anemias from inheritable hemoglobinopathies, such as thalassemia, sickle cell anemia, and spherocytosis (Fig 9) (1,5). CONGENITAL
SKELETAL
DYSPLASIAS
Cleidocranial dysostosis is an autosomal dominant disorder with a wide range of manifestations (3). At birth, the cranial sutures widen and the fontanelles enlarge, reflecting the incomplete ossification of the cranial bones. These changes may persist into adult life (2). As the child grows, the skull is often large and brachycephalic, with frontal and parietal bossing. Other features may include persistently widened sutures or delayed closure, wormian bones, and delayed eruption of the supernumerary teeth, as well as rudimentary small clavicles. In severe cases, the basilar angle is increased (Fig 10) (3). Osteogenesis imperfecta is an inheritable disorder of collagen formation, which results in fragile, lax ligaments. Four main types of osteogenesis imperfecta exist; type 1 (an autosomal-dominant disorder) is the most common. Regardless of the type, if the affected child survives the neonatal period, the cranium assumes a "tamo'shanter" shape and is osteopenic, with the presence of multiple wormian bones and basilar invagination (Fig 11) (4,5).
Figure 11. Osteogenesis imperfecta. Lateral skull radiograph of an 18-year-old man with osteogenesis imperfecta (tarda type) shows areas of undermineralization involving the anterior parietal and occipital regions with basilar invagination.
Mucopolysaccharidoses are a group of closely related syndromes that result from genetic deficiencies of specific lysosomal enzymes involved in the degradation of acid mucopolysaccharides (6). The most common mucopolysaccharidosis is Hurler syndrome, previously called "dysostosis multiplex," which is an autosomal-recessive disorder. The features in Hurler syndrome occur to a varying degree in the other disorders. The skull is large and dolichocephalic, and the calvaria is thickened.
135
Figure 12. Hurler syndrome. Lateral skull radiograph of a 16-month-old girl shows a mild increase in the ventrodorsal dimension of the calvaria and a Jshaped configuration to the sella. Hypoplasia of the maxillary sinuses was also noted.
The sinuses are poorly developed. The sella is enlarged anteriorly and is referred to as "J-shaped" (Fig 12) (2). Fibrous dysplasia is a benign disorder of bone characterized by slow, progressive replacement of a localized area of bone by abnormal fibrous tissue. Fibrous dysplasia occurs in three distinctive, but sometimes overlapping, patterns: monostotic dysplasia (70%), polyostotic dysplasia (25%), and polyostotic fibrous dysplasia or McCune-Albright syndrome (3%-5%), which is characterized by caf6 au lait skin pigmentation and endocrine dysfunction (1). All forms of fibrous dysplasia may involve the skull. Thickening and sclerosis can affect the calvaria, skull base, and facial bones (2). In some instances, the lesions may be a mixture of sclerotic and lytic (4). Extensive sclerosis and bone expansion predominates in the skull base and sphenoid wings. The lesions may show increased activity at radionuclide bone scanning (Fig 13) (3). Neurofibromatosis is a neurocutaneous syndrome that is inherited by autosomal dominant transmission (1). Neurofibromatosis is divided into type 1 (von Recklinghausen disease) and type 2 (7). Skeletal features are common in patients with type 1 neurofibromatosis. With type 1, there is usually a unilateral dysplasia of the greater and lesser wings of the sphenoid, with subsequent asymmetry of the cranial vault and orbit and enlargement of the ipsilateral middle cranial fossa. Hypoplasia of the ipsilateral ethmoid and maxillary sinuses may also be noted. Optic neuromas and acoustic neuromas produce changes in the
136
Figure 13. Fibrous dysplasia. Frontal skull radiograph of a 4-year old girl with McCune-Albright syndrome shows thickening and sclerosis of the lateral roof of the left orbit (arrow).
adjacent bone. A unilateral bone defect along the lambdoid suture is highly suggestive of neurofibromatosis (Fig 14) (1,5). Encephaloceles are herniations of the brain and leptomeninges through a skull defect (cranium bifidum), secondary to failure of the skull and dura to close over the brain (2,7). Occasionally, hemorrhage may occur within the sac. The calvarial defects are most often midline; occipital encephaloceles are the most common (4,7). Uncommonly, the bone defect may be located laterally or in the skull base, with herniation of brain contents into the orbits, paranasal sinuses, or nasopharynx (4). Cranium bifidum occultum is a small cranial defect without associated herniation (Fig 15) (2).
Caput succedaneum, or scalp swelling, is commonly seen in newborn babies and results from subcutaneous edema and hemorrhage. Caput succedaneum disappears after several days without underlying calvarial changes. Subgaleal hematoma is a hematoma underneath the aponeurosis of the scalp and may be severe, resulting in marked blood loss. Caput succedaneum and subgaleal hematoma can cross suture lines and, if severe, can extend to the face and neck. In comparison, a cephalohematoma
Vol 6, No 2, February 1999
IMAGING OF THE CRANIUM
Figure14. Neurofibromatosis. (a) Plain radiograph of a 16-year-old boy show an enlarged left orbit. The lesser wing of the sphenoid was not visualized ("empty orbit sign"). (b) T1 -weighted (repetition time, 500 msec; echo time, 12 msec) axial MR image of same patient shows left sphenoid wing hypoplasia, with compensatory enlargement of the subarachnoid space.
a,
b.
Figure 15. Nasoethmoidal encephaloceles, Threedimensional CT scan of the skull of a 14-year-old boy born with hypertelorism and a facial mass between the orbits demonstrates the defects in the medial orbital walls (arrow).
is subperiosteal and is confined by the sutural margins because of fixation of the periosteum at the sagittal, coronal, and lambdoidal sutures. Occasionally, an associated fracture in the underlying bone or cortical offset of the suture represents molding of the calvaria during delivery. Cephalohematomas start to ossify peripherally at about 2-3 weeks; this gives rise to irregular areas of radiolucency defect in the calvaria when seen en face. This defect gradually ossifies centrally over a period of months. Most of the smooth, convex bone thickening of the skull
Figure 16. Cephalohematoma. Axial CT scan of the skull of a 6-month-old female infant with a cephalohematema at birth shows widening and sclerosis of the left posterior parietal portion of the skull, consistent with an ossified cephalohematoma
that is produced will be absorbed gradually over months or, in some cases, years. In some cases, a defect is formed at the site and is seen as radiolucent cystlike changes to the calvaria (Fig 16) (2,8). This defect may persist for months or years. Leptomeningeal cysts are caused by a traumatic tear in the dura, with outpouching of arachnoid membrane through the overlying fracture line, The suture or fracture
137
Figure17, Leptomeningeal cyst. (a) Frontal skull radiograph of 9-month-old male infant involved in a motor vehicle accident shows a left parietal linear skull fracture. (b) Frontal skull radiograph obtained from same patient 4 months later shows an interval enlargement of the anterior fontanelle and an increase in separation of the left parietal fracture fragments (growing fracture).
a,
b.
is eventually widened secondary to cerebrospinal fluid pulsations--hence, the term "growing fracture." This fracture appears as a growing lytic skull defect on CT scans or plain radiographs. Partially healed fractures are the clue to the diagnosis (Fig 17) (2).
Osseous hemangiomas are infrequently encountered (3). They are composed of fibrous tissue and fat interspersed between vascular spaces. They are usually solitary, and the skull, facial bones, and vertebrae are common sites of involvement. On plain skull radiographs, they appear as lytic lesions with radial striations (Fig 18) (4). Epidermoidomas, or cholesteatomas, are ectodermal rests that may be located within the scalp, diploic space of the skull, or the dura. Regardless of location, they may produce local bone destruction and usually appear as well-defined, round or oval radiolucent loci with sclerotic margins. They are usually benign and slow growing (Fig 19) (4). Histiocytosis X, or Langerhans cell histiocytosis, is a disease characterized by proliferation of a specific histiocyte called the Langerhans cell. Histiocytosis X was previously divided into three overlapping entities: (a) Letterer-Siwe disease, or systemic histiocytosis, which oc-
138
Figure 18. Hemangioma. Lateral skull radiograph of a 15-year-old girl with a chief complaint of headaches shows a large stellate radiolucent defect (arrow) in the left parietal bone, with a radial "sunburst" pattern.
curs in infants and is manifested mostly by rapid progression and visceral involvement, (b) Hand-Schtiller-Christian syndrome, which is a triad of lytic skull lesions, exophthalmos, and diabetes insipidus, and (c) eosinophilic granuloma, which occurs in older children and adults and manifests as single or multiple bone lesions (6). Lesions in the skull are common and appear as punched-out radiolucent defects (Fig 20). Calvarial lesions are more fre-
a.
b.
Figure 21. Metastatic neuroblastoma. (a) Lateral skull radiograph of a 4-year-old boy with a history of abdominal neuroblastoma shows a widened and sclerotic coronal suture. Patient had undergone surgical resection and was currently undergoing chemotherapy, (b) Tl-weighted sagittal MR image (repetition time, 500 msec; echo time, 12 msec) of same patient obtained after injection of gadopentetate dimeglumine shows a subdural metastasis with extension into the coronal suture.
Figure 19. Epidermoid tumor. Lateral skull radiograph from a 21/2-year-old girl with a 6-month history of a left occipital scalp mass shows a small rounded defect in the left occipital area of the skull (arrow). A sclerotic margin is not well seen.
quent than basilar lesions, with 30% occurring in the temporal bone. Activity on a bone scan is often increased (2). Neuroblastoma is the most c o m m o n metastatic tumor to the skull in children. In cases of neuroblastoma, an associated tumor mass usually exists deep to the affected calvaria, with generalized dural metastasis. Neuroblastoma tumor plaques may show hyperattenuation on unenhanced CT studies. Plain skull radiographs show one or
Figure 20. Histiocytosis X. Axial CT scan of the skull of an 8-month-old girl shows a 2-cm lytic lesion of the left frontal bone; differential erosion of the outer and inner tables gives the appearance of a "beveled edge."
several poorly marginated lyric lesions, with apparent widening of the involved suture (Fig 21) (4). Metastasis to the skull may also be seen in leukemia, Wilms tumor, osteosarcoma (often blastic), and Ewing sarcoma (2). Retinoblastomas are the most common intraocular tu-
139
mors in children. When inherited by autosomal dominance transmission, two-thirds of these tumors are bilateral. Plain radiographs of these tumors show intraorbital calcifications, and the diagnosis is often made with CT imaging (Fig 22) (4). Osteosarcomas are rare complications in nonirradiated patients with retinoblastoma. However, they are the most common radiation-induced malignant tumors in those patients with retinoblastoma who have been treated with radiation (9). IEFERENCE~
1. Resnick D. Diagnosis of bone and joint disorder. Philadelphia, Pa: Saunders, 1995. 2. Silverman F, ed. Caffey's pediatric x-ray diagnosis: an integrated imaging approach. 8th ed. Chicago, II1: Year Book Medical, 1985. 3. Blickman J. Pediatric radiology. St Louis, Mo: Mosby-Year Book, 1994. 4. Silverman F, Kuhn J, eds. Essentials of Caffey's pediatric x-ray diagnosis. St Louis, Me: Mosby-Year Book, 1990. 5. Wyngaarden J, Smith L, Bennett JC, eds. Cecil textbook of medicine. Philadelphia, Pa: Saunders, 1992. 6. Cotran R, Kumar V, Robbins S. Robbins pathologic basis of disease. 4th ed. Philadelphia, Pa: Saunders, 1989. 7. Brant W, Helms C. Fundamentals of diagnostic radiology. Baltimore, Md: Williams & Wilkins, 1994. 8. Reed M. Pediatric skeletal radiology. Baltimore, Md: William & Wilkins, 1992. 9. Miller J. Imaging in pediatric oncology. Baltimore, Md: Williams & Wilkins, 1985.
140
F i g u r e 22. Retinoblastorna. Frontal skull radiograph in a 1-year-old child with bilateral retinoblastoma. Note the calcifications (arrows) in both orbits.
The calvaria and its contours can be distorted by a number of diseases. Often the involvement is so characteristic that the pathologic diagnosis can be suggested simply from the cranial imaging. Occasionally the skull is deformed secondarily, reflecting only the status of the brain or meninges. In either case the radiologist is the primary person able to detect the abnormality, assess its importance, and suggest further definitive testing. In this pictorial essay, we will demonstrate 22 different entities that involve the cranium. The primary imaging modalities will be conventional radiography, axial and three-dimensional computed tomography (CT), magnetic resonance (MR) imaging, and ultrasound (US) imaging.
Anencephaly is the most common congenital malformation of the brain. The calvarial vault is absent above the orbit, and the cerebral hemispheres are replaced by malformed brain or angiodysplastic tissue (1). When this condition is diagnosed in utero, US shows no echogenic evidence of an overlying calvaria. Large tufts of moderately echogenic tissue extending superiorly from the top of the head, consistent with the appearance of angiodysplastic tissue, are often seen (Fig 1) (2).
Acad Radio11999; 6:132-140
1From the Division of Pediatric Radiology, Loma Linda University Children's Hospital, 11234 AndersonSt, Loma Linda, CA 92354. ReceivedMarch 16, 1998; revision requested March 19; revision received June 19; accepted
August 19. Address reprint requests to M.S.M. ©AUR, 1999
132
Figure 1. Anencephaly. Lateral plain radiograph of a stillborn neonate shows that the calvaria is absent and the basal bones of the skull are thickened. The orbits are shallow, and the eyes are protuber-
ant.
Craniosynostosis or premature closure of one or more sutures results in distortion of the calvarial configuration. Craniosynostosis is classified as a primary, isolated event of unknown etiology or as secondary to other disease processes, such as rickets and hypophosphatasia (3). It results in a decrease in the skull diameter perpendicular to the closed suture or sutures and compensatory growth in the remaining sutures, causing characteristic skull deformities (4). Dolichocephaly (premature closure of the sagittal suture) accounts for 50% of all cases of craniosynostosis and an increased anteroposterior and decreased biparietal diameter (Fig 2). Brachycephaly (premature bilateral closure of the coronal or lambdoid sutures or
Vol 6, No 2, February 1999
Figure2. Dolichocephaly. Three-dimensional CT scan of the skull of a 5-month-old male infant demonstrates mild elongation of the skull, with open coronal and lambdoidal sutures and fusion of the sagittal suture. The calvaria is elongated ventrodorsally, and the coronal suture is mildly widened.
IMAGING OF THE CRANIUM
Figure4. Plagiocephaly. Three-dimensionaICT scan of the skull of a 3-month-old female infant shows premature fusion of the right coronal suture and mild asymmetry to the orbits and skull.
in expansion of the greater wings of the sphenoid and elevation of the lesser wings, giving a "harlequin" appearance to the orbits (4). The orbits are often shallow, with maxillary hypoplasia (3). Plagiocephaly (unilateral premature closure of the coronal or lambdoid sutures or both) results in asymmetric deformity of the skull (Fig 4). Trigonocephaly results from fusion of the metopic suture in utero, causing a decrease in the transverse dimension of the anterior cranium. The forehead is triangular in shape, and the interorbital distance is decreased (Fig 5). Kleeblattsch~del or "cloverleaf' skull is the result of premature fusion of all the cranial sutures. It is often accompanied by facial dysmorphism, hypotelorism, hydrocephalus, and mental retardation. Radiographic studies show the classical trilobed configuration of the skull with increased convolutional markings (Fig 6) (4). Figure3. Brachycephaly. Three-dimensional CT scan of the skull of a 3-month-old female infant shows a shallow anterior cranial fossa, with bilateral fused coronal sutures and marked diastasis of the sagittal suture. Additional views (not shown) showed a decrease in the anteroposterior diameter of the skull and an apparent increase in the craniocaudal dimension of the skull.
both) results in a decreased anteroposterior diameter of the skull (Fig 3). In bilateral coronal craniosynostosis, the compensatory growth in the transverse dimension results
Permanent calvarial markings can be secondary to liickensch~idel, increased intracranial pressure, or a normal growth spurt. Lacunar skull, or liickensch~idel, is a bone dysplasia of the calvaria that is present at birth and usually disappears by 4-6 months of age. It is not related to hydrocephalus and is almost always associated with meningocele or encephalomeningocele and an ArnoldChiari type 2 malformation (2,4). Plain skull radiographs
133
Figure 5. Trigonocephaly. Three-dimensional CT scan of the skull of a 5-month-old female infant demonstrates hypotelodsm and prominent ridging of the fused metopic suture.
Figure 6. Kleeblattsch&del. Axial CT scan of the skull of a 24-day-old male infant shows calvarial scalloping and bulging of the temporal bones, causing a trilobed (cloverleaf) appearance.
show a characteristic "soap bubble" appearance, usually involving the parietal and occipital bones (Fig 7) (4). Increased intracranial pressure in a child may be accompanied by calvarial changes. The cranial vault may be enlarged, and the sutures, including the fontanelle, may be diastatic on plain radiographs of the skull. In addition, there may be enlargement and deformity of the sella and an increase in the convolutional markings of the calvaria. CT imaging is helpful in showing early changes, such as subtle spreading of the sutures and mild ventriculomegaly. Late findings are obvious on axial CT
134
Figure 7. L0ckensch&del. Lateral skull radiograph of a 4-month-old female infant with Chiari malformation in whom a spinal myelomeningocele had been repaired at birth shows a scalloped appearance throughout the skull, most prominent in the parieto-occipital regions.
Figure 8. Hydrocephalus. Lateral skull radiograph of a 23-month-old girl with hydrocephalus secondary to shunt malfunction demonstrates widening of the coronal and lambdoidal sutures and slight enlargement of the sella turcica. No convolutional markings are seen.
images, which show severe ventricular dilatation (Fig 8) (2). DIFFUSE SKULL THICKENING In fetal life, hematopoiesis occurs throughout the reticuloendothelial system. Shortly after birth, however, the terminal differentiation of blood precursors resides
Vol 6, No 2, February 1999
IMAGING OF THE CRANIUM
Figure 9. Thalassemia. Lateral skull radiograph demonstrates a widened spiculated calvaria, the "hairon-end" appearance to the skull, secondary to expansion of the marrow space.
Figure 10. Cleidocranial dysplasia. Lateral skull radiograph of an 18-year-old man shows thickening of the frontal bone and multiple wormian bones in the larnbdoidal suture. Note that the permanent teeth have failed to erupt.
predominantly in the marrow cavities of the axial skeleton and the skull. The diploic space is highly expandable when the demand for blood cell production is increased, as it is in patients with chronic hemolytic anemias from inheritable hemoglobinopathies, such as thalassemia, sickle cell anemia, and spherocytosis (Fig 9) (1,5). CONGENITAL
SKELETAL
DYSPLASIAS
Cleidocranial dysostosis is an autosomal dominant disorder with a wide range of manifestations (3). At birth, the cranial sutures widen and the fontanelles enlarge, reflecting the incomplete ossification of the cranial bones. These changes may persist into adult life (2). As the child grows, the skull is often large and brachycephalic, with frontal and parietal bossing. Other features may include persistently widened sutures or delayed closure, wormian bones, and delayed eruption of the supernumerary teeth, as well as rudimentary small clavicles. In severe cases, the basilar angle is increased (Fig 10) (3). Osteogenesis imperfecta is an inheritable disorder of collagen formation, which results in fragile, lax ligaments. Four main types of osteogenesis imperfecta exist; type 1 (an autosomal-dominant disorder) is the most common. Regardless of the type, if the affected child survives the neonatal period, the cranium assumes a "tamo'shanter" shape and is osteopenic, with the presence of multiple wormian bones and basilar invagination (Fig 11) (4,5).
Figure 11. Osteogenesis imperfecta. Lateral skull radiograph of an 18-year-old man with osteogenesis imperfecta (tarda type) shows areas of undermineralization involving the anterior parietal and occipital regions with basilar invagination.
Mucopolysaccharidoses are a group of closely related syndromes that result from genetic deficiencies of specific lysosomal enzymes involved in the degradation of acid mucopolysaccharides (6). The most common mucopolysaccharidosis is Hurler syndrome, previously called "dysostosis multiplex," which is an autosomal-recessive disorder. The features in Hurler syndrome occur to a varying degree in the other disorders. The skull is large and dolichocephalic, and the calvaria is thickened.
135
Figure 12. Hurler syndrome. Lateral skull radiograph of a 16-month-old girl shows a mild increase in the ventrodorsal dimension of the calvaria and a Jshaped configuration to the sella. Hypoplasia of the maxillary sinuses was also noted.
The sinuses are poorly developed. The sella is enlarged anteriorly and is referred to as "J-shaped" (Fig 12) (2). Fibrous dysplasia is a benign disorder of bone characterized by slow, progressive replacement of a localized area of bone by abnormal fibrous tissue. Fibrous dysplasia occurs in three distinctive, but sometimes overlapping, patterns: monostotic dysplasia (70%), polyostotic dysplasia (25%), and polyostotic fibrous dysplasia or McCune-Albright syndrome (3%-5%), which is characterized by caf6 au lait skin pigmentation and endocrine dysfunction (1). All forms of fibrous dysplasia may involve the skull. Thickening and sclerosis can affect the calvaria, skull base, and facial bones (2). In some instances, the lesions may be a mixture of sclerotic and lytic (4). Extensive sclerosis and bone expansion predominates in the skull base and sphenoid wings. The lesions may show increased activity at radionuclide bone scanning (Fig 13) (3). Neurofibromatosis is a neurocutaneous syndrome that is inherited by autosomal dominant transmission (1). Neurofibromatosis is divided into type 1 (von Recklinghausen disease) and type 2 (7). Skeletal features are common in patients with type 1 neurofibromatosis. With type 1, there is usually a unilateral dysplasia of the greater and lesser wings of the sphenoid, with subsequent asymmetry of the cranial vault and orbit and enlargement of the ipsilateral middle cranial fossa. Hypoplasia of the ipsilateral ethmoid and maxillary sinuses may also be noted. Optic neuromas and acoustic neuromas produce changes in the
136
Figure 13. Fibrous dysplasia. Frontal skull radiograph of a 4-year old girl with McCune-Albright syndrome shows thickening and sclerosis of the lateral roof of the left orbit (arrow).
adjacent bone. A unilateral bone defect along the lambdoid suture is highly suggestive of neurofibromatosis (Fig 14) (1,5). Encephaloceles are herniations of the brain and leptomeninges through a skull defect (cranium bifidum), secondary to failure of the skull and dura to close over the brain (2,7). Occasionally, hemorrhage may occur within the sac. The calvarial defects are most often midline; occipital encephaloceles are the most common (4,7). Uncommonly, the bone defect may be located laterally or in the skull base, with herniation of brain contents into the orbits, paranasal sinuses, or nasopharynx (4). Cranium bifidum occultum is a small cranial defect without associated herniation (Fig 15) (2).
Caput succedaneum, or scalp swelling, is commonly seen in newborn babies and results from subcutaneous edema and hemorrhage. Caput succedaneum disappears after several days without underlying calvarial changes. Subgaleal hematoma is a hematoma underneath the aponeurosis of the scalp and may be severe, resulting in marked blood loss. Caput succedaneum and subgaleal hematoma can cross suture lines and, if severe, can extend to the face and neck. In comparison, a cephalohematoma
Vol 6, No 2, February 1999
IMAGING OF THE CRANIUM
Figure14. Neurofibromatosis. (a) Plain radiograph of a 16-year-old boy show an enlarged left orbit. The lesser wing of the sphenoid was not visualized ("empty orbit sign"). (b) T1 -weighted (repetition time, 500 msec; echo time, 12 msec) axial MR image of same patient shows left sphenoid wing hypoplasia, with compensatory enlargement of the subarachnoid space.
a,
b.
Figure 15. Nasoethmoidal encephaloceles, Threedimensional CT scan of the skull of a 14-year-old boy born with hypertelorism and a facial mass between the orbits demonstrates the defects in the medial orbital walls (arrow).
is subperiosteal and is confined by the sutural margins because of fixation of the periosteum at the sagittal, coronal, and lambdoidal sutures. Occasionally, an associated fracture in the underlying bone or cortical offset of the suture represents molding of the calvaria during delivery. Cephalohematomas start to ossify peripherally at about 2-3 weeks; this gives rise to irregular areas of radiolucency defect in the calvaria when seen en face. This defect gradually ossifies centrally over a period of months. Most of the smooth, convex bone thickening of the skull
Figure 16. Cephalohematoma. Axial CT scan of the skull of a 6-month-old female infant with a cephalohematema at birth shows widening and sclerosis of the left posterior parietal portion of the skull, consistent with an ossified cephalohematoma
that is produced will be absorbed gradually over months or, in some cases, years. In some cases, a defect is formed at the site and is seen as radiolucent cystlike changes to the calvaria (Fig 16) (2,8). This defect may persist for months or years. Leptomeningeal cysts are caused by a traumatic tear in the dura, with outpouching of arachnoid membrane through the overlying fracture line, The suture or fracture
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Figure17, Leptomeningeal cyst. (a) Frontal skull radiograph of 9-month-old male infant involved in a motor vehicle accident shows a left parietal linear skull fracture. (b) Frontal skull radiograph obtained from same patient 4 months later shows an interval enlargement of the anterior fontanelle and an increase in separation of the left parietal fracture fragments (growing fracture).
a,
b.
is eventually widened secondary to cerebrospinal fluid pulsations--hence, the term "growing fracture." This fracture appears as a growing lytic skull defect on CT scans or plain radiographs. Partially healed fractures are the clue to the diagnosis (Fig 17) (2).
Osseous hemangiomas are infrequently encountered (3). They are composed of fibrous tissue and fat interspersed between vascular spaces. They are usually solitary, and the skull, facial bones, and vertebrae are common sites of involvement. On plain skull radiographs, they appear as lytic lesions with radial striations (Fig 18) (4). Epidermoidomas, or cholesteatomas, are ectodermal rests that may be located within the scalp, diploic space of the skull, or the dura. Regardless of location, they may produce local bone destruction and usually appear as well-defined, round or oval radiolucent loci with sclerotic margins. They are usually benign and slow growing (Fig 19) (4). Histiocytosis X, or Langerhans cell histiocytosis, is a disease characterized by proliferation of a specific histiocyte called the Langerhans cell. Histiocytosis X was previously divided into three overlapping entities: (a) Letterer-Siwe disease, or systemic histiocytosis, which oc-
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Figure 18. Hemangioma. Lateral skull radiograph of a 15-year-old girl with a chief complaint of headaches shows a large stellate radiolucent defect (arrow) in the left parietal bone, with a radial "sunburst" pattern.
curs in infants and is manifested mostly by rapid progression and visceral involvement, (b) Hand-Schtiller-Christian syndrome, which is a triad of lytic skull lesions, exophthalmos, and diabetes insipidus, and (c) eosinophilic granuloma, which occurs in older children and adults and manifests as single or multiple bone lesions (6). Lesions in the skull are common and appear as punched-out radiolucent defects (Fig 20). Calvarial lesions are more fre-
a.
b.
Figure 21. Metastatic neuroblastoma. (a) Lateral skull radiograph of a 4-year-old boy with a history of abdominal neuroblastoma shows a widened and sclerotic coronal suture. Patient had undergone surgical resection and was currently undergoing chemotherapy, (b) Tl-weighted sagittal MR image (repetition time, 500 msec; echo time, 12 msec) of same patient obtained after injection of gadopentetate dimeglumine shows a subdural metastasis with extension into the coronal suture.
Figure 19. Epidermoid tumor. Lateral skull radiograph from a 21/2-year-old girl with a 6-month history of a left occipital scalp mass shows a small rounded defect in the left occipital area of the skull (arrow). A sclerotic margin is not well seen.
quent than basilar lesions, with 30% occurring in the temporal bone. Activity on a bone scan is often increased (2). Neuroblastoma is the most c o m m o n metastatic tumor to the skull in children. In cases of neuroblastoma, an associated tumor mass usually exists deep to the affected calvaria, with generalized dural metastasis. Neuroblastoma tumor plaques may show hyperattenuation on unenhanced CT studies. Plain skull radiographs show one or
Figure 20. Histiocytosis X. Axial CT scan of the skull of an 8-month-old girl shows a 2-cm lytic lesion of the left frontal bone; differential erosion of the outer and inner tables gives the appearance of a "beveled edge."
several poorly marginated lyric lesions, with apparent widening of the involved suture (Fig 21) (4). Metastasis to the skull may also be seen in leukemia, Wilms tumor, osteosarcoma (often blastic), and Ewing sarcoma (2). Retinoblastomas are the most common intraocular tu-
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mors in children. When inherited by autosomal dominance transmission, two-thirds of these tumors are bilateral. Plain radiographs of these tumors show intraorbital calcifications, and the diagnosis is often made with CT imaging (Fig 22) (4). Osteosarcomas are rare complications in nonirradiated patients with retinoblastoma. However, they are the most common radiation-induced malignant tumors in those patients with retinoblastoma who have been treated with radiation (9). IEFERENCE~
1. Resnick D. Diagnosis of bone and joint disorder. Philadelphia, Pa: Saunders, 1995. 2. Silverman F, ed. Caffey's pediatric x-ray diagnosis: an integrated imaging approach. 8th ed. Chicago, II1: Year Book Medical, 1985. 3. Blickman J. Pediatric radiology. St Louis, Mo: Mosby-Year Book, 1994. 4. Silverman F, Kuhn J, eds. Essentials of Caffey's pediatric x-ray diagnosis. St Louis, Me: Mosby-Year Book, 1990. 5. Wyngaarden J, Smith L, Bennett JC, eds. Cecil textbook of medicine. Philadelphia, Pa: Saunders, 1992. 6. Cotran R, Kumar V, Robbins S. Robbins pathologic basis of disease. 4th ed. Philadelphia, Pa: Saunders, 1989. 7. Brant W, Helms C. Fundamentals of diagnostic radiology. Baltimore, Md: Williams & Wilkins, 1994. 8. Reed M. Pediatric skeletal radiology. Baltimore, Md: William & Wilkins, 1992. 9. Miller J. Imaging in pediatric oncology. Baltimore, Md: Williams & Wilkins, 1985.
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F i g u r e 22. Retinoblastorna. Frontal skull radiograph in a 1-year-old child with bilateral retinoblastoma. Note the calcifications (arrows) in both orbits.