British Journal of Radiology (2003) 76, 503-504
© 2003 British Institute of Radiology
doi: 10.1259/bjr/56902821
A case of big bad bones
P S Richards, MRCP, FRCR and
A D King, MRCP, FRCR
Department of Diagnostic Radiology and Organ Imaging, Faculty of Medicine, The Chinese University of Hong Kong, Prince of Wales Hospital, Ngan Shing Street, Shatin, New Territories, Hong Kong SAR, China
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Introduction
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This 24-year-old man presented at the age of 9 years with facial deformity and pathological fractures of the humerus and femur. There was no evidence of precocious puberty or skin lesions. At the age of 14 he developed refractory thyrotoxicosis requiring radioactive iodine therapy. At that time he was noted to be tall for his age with large hands and feet and a broad nose (Figures 1–3
). What is the diagnosis?
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Discussion
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The axial CT and MR images of the skull base show diffuse hyperostosis and bony expansion with areas of ground glass texture and several intraosseous cysts in keeping with advanced polyostotic fibrous dysplasia (Figures 1 and 2
). The coronal T1 weighted gadolinium enhanced MRI of the pituitary fossa shows an enlarged pituitary gland elevated by the thickened floor of the sella (Figure 3). There was no evidence of a microadenoma. Serum insulin-like growth factor-1 was mildly elevated and there was failure of growth hormone (GH) suppression during a glucose tolerance test.
The patient suffers from McCune-Albright syndrome (MCAS) associated with thyrotoxicosis and acromegaly. MCAS was classically defined as a triad of polyostotic fibrous dysplasia, café-au-lait pigmentation and precocious puberty [1]. However, it is increasingly recognised as a heterogeneous clinical condition causing autonomous hyperfunction of multiple endocrine systems resulting from the mosaic expression of a post-zygotic activating mutation in the gene that encodes the alpha sub-unit of stimulatory G protein [2].
An association between MCAS and gigantism is well recognised with around 30 reported cases in the literature [3]. Diagnosis is often hampered by the fact that GH levels are usually only mildly elevated in MCAS and may be masked by the presence of precocious puberty or thyrotoxicosis. Furthermore, the clinical features of gigantism are often hidden by craniofacial deformity.
GH hypersecretion is associated with hyperprolactinaemia in 70–80% of cases in MCAS compared with around 40% in isolated acromegaly. The exact pathophysiology is enigmatic. Reported histological findings range from normal (suggesting hypothalamic-pituitary dysfunction) to autonomous hyperplasia of plurimorphous mammosomatotrophs and pituitary adenomas. The latter have been confirmed in around a third of reported cases [3].
Pituitary surgery is hazardous in these patients because the dysplastic bone is highly vascular. Furthermore, hyperostosis and expansion of the skull base often render surgery anatomically unfeasible. Fractionated radiotherapy is usually avoided because there is an increased risk of post-irradiation osteosarcoma in fibrous dysplasia. Stereotactic radiosurgery has been used successfully in selected patients but increasingly, as in this case, the acromegaly is managed conservatively with bromocriptine and long-acting somatostatin analogues, keeping stereotactic radiosurgery in reserve [3].
More recently the patient has developed increasingly severe occipital headache and upper limb hypereflexia.
The sagittal T1 weighted MRI of the cervical spine demonstrates tonsillar ectopia and a syrinx extending from C1 to C5/6 (Figure 4) for which posterior fossa decompression may be considered in the future. There are a few reports of cerebellar tonsillar herniation and syringomyelia associated with monostotic fibrous dysplasia of the occiput [4]. To the best of our knowledge this is the first report of an association with MCAS.
Received for publication February 12, 2002.
Accepted for publication May 23, 2002.
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References
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- de Sanctis C, Lala R, Matarazzo P, Balsamo A, Bergarmaschi R, Cappa M, et al. McCune-Albright Syndrome: a longitudinal clinical study of 32 patients. J Pediatr Endocrinol 1999;12:817–26.
- Cohen MM, Howell RE. Etiology of fibrous dysplasia and McCune-Albright syndrome. Int J Oral Maxillofac Surg 1999;28:366–71.[CrossRef][Medline]
- Sakaki S, Yokoyama S, Mamitsuka K, Nakayama M, Goto M, Kuratsu J. A case of pituitary adenoma associated with McCune-Albright syndrome. Pituitary 1999;1:297–302.[Medline]
- Chandy MJ. Occipital fibrous dysplasia, tonsillar herniation and cervical syringomyelia. Br J Neurosurg 1999;13:217–8.[Medline]
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Introduction
Discussion
