Skeletal Radiot (1992) 21:396-398
Skeletal Radiology
Case report 746 P.F. Cook, M.D., and S.G. Moore, M.D. Stanford University School of Medicine, Stanford, California, USA
Fig. 1. Anteroposterior radiograph of the arm shows obliteration of the marrow space, osteosclerosis, metaphyseal clubbing, transverse lucent metaphyseal bands (radius), and bone within a bone appearance (metacarpals), which are characteristic Fig. 2. Lateral view of the skull with expansion of the diploic space and prominent hair-on-end appearance
Fig. 3. Midline sagittal Tl-weighted (600/20) magnetic resonance (MR) image reveals alternating bands of low and intermediate signal intensity in the diploic space corresponding to interspersed dense trabeculae and marrow. The base of the skull and inner table are markedly thickened, with low signal intensity dense bone Fig. 4. A Midline sagittal T2-weighted (2500/80) and B short tan inversion recovery (STIR) (1500/30/150) M R images of the head, show alternating bands in the diploic space of thickened trabecular bone seen as low to intermediate signal intensity on Tl-weighted, T2-weighted, and STIR images. Interposed hematopoietic marrow has increased signal intensity on STIR and T2 weighted images 9 1992 International Skeletal Society
P.F. Cook and S.G. Moore: Case report 746 Clinical information
This 14-year-old Hispanic girl was originally diagnosed as having osteopetrosis at the age of 3 months, having presented with hepatosplenomegaly. At age 2 years, she developed pancytopenia, resulting in the institution of steroid therapy. Clinically, her anemia has been mild, and she has only required intraoperative blood transfusions for loss of blood resulting from surgical procedures to liberate her optic nerves and to institute drainage of mastoiditis. She has had multiple fractures. Physical examination was remarkable for an enlarged calvarium, particularly at the vertex, and almost complete blindness. The patient had the following hematological parameters: hemoglobin 11.8 gm/dl, hematocrit 35%, white blood cell count reprint requests to: Sheila G. Moore, M.D., Department of Radiology, S058A, Stanford University Medical Center, Stanford, CA 94305, USA
Address
397 (WBC) 6900/gl (61% neutrophils, 32% lymphocytes, 7% monocytes), platelets 383 K/gl, and mean corpuscular volume (MCV) 84 ft. A skeletal survey revealed the classic features of osteopetrosis: generalized osteosclerosis, bone withina-bone appearance, absence of differentiation of the medullary cavity and the cortex, metaphyseal clubbing, lucent transverse bands in the long bones, prominence of the anterior vascular notches in the vertebral bodies, absence of the paranasal sinuses, and thickening of the base of the skull (Fig. 1). Plain radiographs of the skull showed a markedly widened diploic space, thickening of the base of the skull, and a prominent hair-on-end appearance (Fig. 2). M R examination of the cranium was performed on a 1.5-T superconducting magnet. Sagittal TIweighted (TR 600 TE 20 ms), T2weighted (TR 2500 TE 80 ms), and short tau inversion recovery (STIR) (TR 1500 TE 30 TI 150 ms) images
were obtained. Transverse TIweighted (TR 800 TE 20 ms) and T2weighted fat saturation (TR 2500 TE 80 ms) images were also obtained. The thickening of the base of the skull was characterized by a signal void on both T1- and T2-weighted images, corresponding to the radiographically observed dense bone and obliteration of the marrow space (Fig. 3). The calvarial inner table was also markedly thickened with low signal intensity on both T1- and T2weighted images. Marked expansion of the diploic space and thinning of the outer table were also present. Alternating bands of low (hypointense to muscle) and intermediate (isointense to muscle) signal intensity on Tl-weighted images were seen as alternating bands of low and increased (hyperintense to muscle) signal intensity on T2-weighted, fat saturation, and STIR images (Fig. 4). These findings were believed to represent alternating bands of dense trabecular bone and hematopoietic marrow.
398
Diagnosis: Osteopetrosis We present a case of osteopetrosis in a child with marked expansion of the diploic space and a hair-on-end appearance of the skull in imaging studies.
Discussion This radiographic appearance has apparently not been previously reported in osteopetrosis. This hair-onend pattern is typically seen in sickle cell disease and thalassemia major and uncommonly observed in congenital cyanotic heart disease, severe iron deficiency anemia, leukemia, lymphoma, and renal cell carcinoma producing erythropoietin [3]. This child has none of these disorders to explain the expansion of her diploic space in the cranium. The M R characteristics of the marrow in osteopetrosis have been reported [6]. In 2 patients, a complete signal void was noted on the T1- and T2-weighted images, indicating obliteration of the marrow space. A third patient had "normal vertebral bodies with high signal" on the Tl-weighted images, indicative of fatty marrow [6]. Our patient, in contrast, had intermediate signal intensity of the marrow in the diploic space on the Tl-weighted images, more typical of hematopoietic marrow. The extramedullary cranial hematopoesis appears to be compensating for the lack of normal marrow space elsewhere in the skeleton, resulting in near-normal hematologic parameters.
P.F. Cook and S.G. Moore: Case report 746 Pathologically, the spicules of bone comprising the calvarial hairon-end radiographic appearance represent compensatory hypertrophy of existing trabeculations, which presumably serve as the bony support for increasing hematopoietic activity in the diploic space. The hypertrophied trabeculations are noted on spin echo M R images as low signal intensity on both T1- and T2weighted images. Since the trabecular bone is lamellated bone, this feature is not surprising [5]. The etiology of expansion of the calvarial marrow in this patient is unclear. Osteopetrosis is characterized by intermittent osteoclastic dysfunction with periods of more normal osteoclastic activity. This alteration in osteoclastic activity is often manifested by lucent lines in the otherwise sclerotic long bones [4]. A lack of the " r u f f l e d " osteoclast border associated with normally functioning osteoclasts is present. Absence of collagenase within the bone is also noted [2]. In summary, osteopetrosis is a disorder characterized by osteoclastic dysfunction [4, 7]. The bones of afflicted patients become sclerotic and show modeling defects resulting in either a decrease or obliteration of the marrow cavity and resultant pancytopenia. Other clinical manifestations include bony deformities, cranial nerve palsies from bony overgrowth, pathological fractures, osteomyelitis, and hepatosplenomegaly secondary to extramedullary hematopoiesis. In the skull, the diploic space is usually decreased or obliterated [4].
Absent or decreased marrow space is observed on plain films. On MRI, the marrow cavity very likely will be obliterated with low signal intensity on T1- and T2-weighted images [1, 6, 8]. We report a case of osteopetrosis in which the diploic space is markedly increased, giving a hair-on-end appearance resembling thalassemia major. Perhaps some local factor within the diploic space prevented the expected osteoclastic dysfunction, allowing remodeling and expansion of the cranial vault. Acknowledgements. We would like to thank
Bertil E. Glader, M.D., for his review of the manuscript.
References 1. Adams BK (1989) Scintigraphy in a patient with complicated osteopetrosis. Clin Nucl Med 14:323 2. Bullough PG, Vigorita VJ (1984) Atlas of orthopaedic pathology. University Park Press, Baltimore, p 322 3. Daly D (1987) "Hair-on-end" pattern in the skull. Semin Roentgenol 22:144 4. Milgram JW, Jasty M (1982) Osteopetrosis. J Bone Joint Surg 64:912 5. Moore SG, Sebag GH, Dawson KL (1989) MR evaluation of cortical bone and periosteal reaction in bone lesion: pathologic and radiographic correlation. Soc Magn Reson Med, Book of Abstracts 1:19
6. Rao VM, Dalinka MK, Mitchell DG, Spritzer CE, et al. (1986) Osteopetrosis: MR characteristics at 1.5 T. Radiology 161:217 7. Resnick D, Niwayama G (1988) Diagnosis of bone and joint disorders, 2nd edn. WB Saunders, Philadelphia, p 3478 8. Silverman FN (1985) Caffey's pediatric X-ray diagnosis, 8th edn. Year Book Medical, Chicago, p 623
Skeletal Radiology
Case report 746 P.F. Cook, M.D., and S.G. Moore, M.D. Stanford University School of Medicine, Stanford, California, USA
Fig. 1. Anteroposterior radiograph of the arm shows obliteration of the marrow space, osteosclerosis, metaphyseal clubbing, transverse lucent metaphyseal bands (radius), and bone within a bone appearance (metacarpals), which are characteristic Fig. 2. Lateral view of the skull with expansion of the diploic space and prominent hair-on-end appearance
Fig. 3. Midline sagittal Tl-weighted (600/20) magnetic resonance (MR) image reveals alternating bands of low and intermediate signal intensity in the diploic space corresponding to interspersed dense trabeculae and marrow. The base of the skull and inner table are markedly thickened, with low signal intensity dense bone Fig. 4. A Midline sagittal T2-weighted (2500/80) and B short tan inversion recovery (STIR) (1500/30/150) M R images of the head, show alternating bands in the diploic space of thickened trabecular bone seen as low to intermediate signal intensity on Tl-weighted, T2-weighted, and STIR images. Interposed hematopoietic marrow has increased signal intensity on STIR and T2 weighted images 9 1992 International Skeletal Society
P.F. Cook and S.G. Moore: Case report 746 Clinical information
This 14-year-old Hispanic girl was originally diagnosed as having osteopetrosis at the age of 3 months, having presented with hepatosplenomegaly. At age 2 years, she developed pancytopenia, resulting in the institution of steroid therapy. Clinically, her anemia has been mild, and she has only required intraoperative blood transfusions for loss of blood resulting from surgical procedures to liberate her optic nerves and to institute drainage of mastoiditis. She has had multiple fractures. Physical examination was remarkable for an enlarged calvarium, particularly at the vertex, and almost complete blindness. The patient had the following hematological parameters: hemoglobin 11.8 gm/dl, hematocrit 35%, white blood cell count reprint requests to: Sheila G. Moore, M.D., Department of Radiology, S058A, Stanford University Medical Center, Stanford, CA 94305, USA
Address
397 (WBC) 6900/gl (61% neutrophils, 32% lymphocytes, 7% monocytes), platelets 383 K/gl, and mean corpuscular volume (MCV) 84 ft. A skeletal survey revealed the classic features of osteopetrosis: generalized osteosclerosis, bone withina-bone appearance, absence of differentiation of the medullary cavity and the cortex, metaphyseal clubbing, lucent transverse bands in the long bones, prominence of the anterior vascular notches in the vertebral bodies, absence of the paranasal sinuses, and thickening of the base of the skull (Fig. 1). Plain radiographs of the skull showed a markedly widened diploic space, thickening of the base of the skull, and a prominent hair-on-end appearance (Fig. 2). M R examination of the cranium was performed on a 1.5-T superconducting magnet. Sagittal TIweighted (TR 600 TE 20 ms), T2weighted (TR 2500 TE 80 ms), and short tau inversion recovery (STIR) (TR 1500 TE 30 TI 150 ms) images
were obtained. Transverse TIweighted (TR 800 TE 20 ms) and T2weighted fat saturation (TR 2500 TE 80 ms) images were also obtained. The thickening of the base of the skull was characterized by a signal void on both T1- and T2-weighted images, corresponding to the radiographically observed dense bone and obliteration of the marrow space (Fig. 3). The calvarial inner table was also markedly thickened with low signal intensity on both T1- and T2weighted images. Marked expansion of the diploic space and thinning of the outer table were also present. Alternating bands of low (hypointense to muscle) and intermediate (isointense to muscle) signal intensity on Tl-weighted images were seen as alternating bands of low and increased (hyperintense to muscle) signal intensity on T2-weighted, fat saturation, and STIR images (Fig. 4). These findings were believed to represent alternating bands of dense trabecular bone and hematopoietic marrow.
398
Diagnosis: Osteopetrosis We present a case of osteopetrosis in a child with marked expansion of the diploic space and a hair-on-end appearance of the skull in imaging studies.
Discussion This radiographic appearance has apparently not been previously reported in osteopetrosis. This hair-onend pattern is typically seen in sickle cell disease and thalassemia major and uncommonly observed in congenital cyanotic heart disease, severe iron deficiency anemia, leukemia, lymphoma, and renal cell carcinoma producing erythropoietin [3]. This child has none of these disorders to explain the expansion of her diploic space in the cranium. The M R characteristics of the marrow in osteopetrosis have been reported [6]. In 2 patients, a complete signal void was noted on the T1- and T2-weighted images, indicating obliteration of the marrow space. A third patient had "normal vertebral bodies with high signal" on the Tl-weighted images, indicative of fatty marrow [6]. Our patient, in contrast, had intermediate signal intensity of the marrow in the diploic space on the Tl-weighted images, more typical of hematopoietic marrow. The extramedullary cranial hematopoesis appears to be compensating for the lack of normal marrow space elsewhere in the skeleton, resulting in near-normal hematologic parameters.
P.F. Cook and S.G. Moore: Case report 746 Pathologically, the spicules of bone comprising the calvarial hairon-end radiographic appearance represent compensatory hypertrophy of existing trabeculations, which presumably serve as the bony support for increasing hematopoietic activity in the diploic space. The hypertrophied trabeculations are noted on spin echo M R images as low signal intensity on both T1- and T2weighted images. Since the trabecular bone is lamellated bone, this feature is not surprising [5]. The etiology of expansion of the calvarial marrow in this patient is unclear. Osteopetrosis is characterized by intermittent osteoclastic dysfunction with periods of more normal osteoclastic activity. This alteration in osteoclastic activity is often manifested by lucent lines in the otherwise sclerotic long bones [4]. A lack of the " r u f f l e d " osteoclast border associated with normally functioning osteoclasts is present. Absence of collagenase within the bone is also noted [2]. In summary, osteopetrosis is a disorder characterized by osteoclastic dysfunction [4, 7]. The bones of afflicted patients become sclerotic and show modeling defects resulting in either a decrease or obliteration of the marrow cavity and resultant pancytopenia. Other clinical manifestations include bony deformities, cranial nerve palsies from bony overgrowth, pathological fractures, osteomyelitis, and hepatosplenomegaly secondary to extramedullary hematopoiesis. In the skull, the diploic space is usually decreased or obliterated [4].
Absent or decreased marrow space is observed on plain films. On MRI, the marrow cavity very likely will be obliterated with low signal intensity on T1- and T2-weighted images [1, 6, 8]. We report a case of osteopetrosis in which the diploic space is markedly increased, giving a hair-on-end appearance resembling thalassemia major. Perhaps some local factor within the diploic space prevented the expected osteoclastic dysfunction, allowing remodeling and expansion of the cranial vault. Acknowledgements. We would like to thank
Bertil E. Glader, M.D., for his review of the manuscript.
References 1. Adams BK (1989) Scintigraphy in a patient with complicated osteopetrosis. Clin Nucl Med 14:323 2. Bullough PG, Vigorita VJ (1984) Atlas of orthopaedic pathology. University Park Press, Baltimore, p 322 3. Daly D (1987) "Hair-on-end" pattern in the skull. Semin Roentgenol 22:144 4. Milgram JW, Jasty M (1982) Osteopetrosis. J Bone Joint Surg 64:912 5. Moore SG, Sebag GH, Dawson KL (1989) MR evaluation of cortical bone and periosteal reaction in bone lesion: pathologic and radiographic correlation. Soc Magn Reson Med, Book of Abstracts 1:19
6. Rao VM, Dalinka MK, Mitchell DG, Spritzer CE, et al. (1986) Osteopetrosis: MR characteristics at 1.5 T. Radiology 161:217 7. Resnick D, Niwayama G (1988) Diagnosis of bone and joint disorders, 2nd edn. WB Saunders, Philadelphia, p 3478 8. Silverman FN (1985) Caffey's pediatric X-ray diagnosis, 8th edn. Year Book Medical, Chicago, p 623
