Calvarial melorheostosis with bilateral parietal bone involvement – an extremely rare case report.

Clinical History

A 50-year-old male patient who had been in a road traffic accident presented to the trauma department in an unconscious state.

Imaging Findings

Non contrast CT head was performed on a 16 slice CT scanner. The patient had multiple linear, skull fractures with subarachnoid hemorrhages. Frontal and both parietal bones showed cortical thickening in a wavy fashion (FIG 1). These hyperostotic lesions mimicked osteochondromas but lacked corticomedullary continuity (FIG 2). Multiple regions of well marginated, undulated cortical hyperostosis were seen contiguous with each other giving a candle wax appearance (FIG 3).

Discussion

Leri and Joanny first described Melorheostosis (also known as candle bone disease, melting wax syndrome, Leri disease) in 1922 [1]. It is a rare nonhereditary sclerosing dysplasia of bone. The classic radiological appearance of 'flowing hyperostosis' resembles hardened wax that has dripped down the side of a candle. The word melorheostosis is derived from greek language meaning "Limb, flow, and bone" which describes the flowing hyperostotic appearance. However, this classic appearance may not be seen in every case.
Melorheostosis has rarely been reported in the axial skeleton [2]. Melorheostosis predominantly affects the appendicular skeleton and is most common in the long bones of extremities, although it can be seen in the hands and feet as well. Skull involvement is very rare [1, 3, 4]. Soft tissue abnormalities consisting of osseous, chondroid, vascular and fibrocartilaginous tissue have been reported in less than 76% cases of melorheostosis [5-7]. Soft tissue changes include anomalous pigmentation, scleroderma-like atrophy of the skin and muscular atrophy. Pressure on adjacent vessels and bursae may lead to vascular occlusion and bursitis [8].
Syndromic associations of melorheostosis are neurofibromatosis, tuberous sclerosis, scleroderma, tricho-dento-osseous syndrome, rheumatoid arthritis, Caffey's disease and hypophosphatemic rickets.
The differential diagnosis for calvarial melorheostosis includes multiple calcified trichilemmal cysts, tumoral calcium pyrophosphate dihydrate deposition disease (CPPD), multiple osteochondromas, periosteal osteosarcoma and ivory osteomas. The unilateral and multifocal cortical locations, distinct imaging features and lack of interval change is characteristic of melorheostosis. MR imaging shows zones of signal void on all pulse sequences corresponding to sites of hyperostosis seen on radiographs and CT. Hyperostosis predominantly involves the outer cortex but may also involved the endosteum with marrow space encroachment; however, marrow adjacent to sites of hyperostosis had normal signal intensity [9]. Bone scintigraphy shows marked radionuclide uptake.
Multiple calcified trichilemmal cysts can be a mimic but are classically subcutaneous and do not show contiguous hyperostosis as seen in our case.
Another important differential is multiple ivory skull osteomata seen mainly in Gardener syndrome. These however are separate, focal lesions, not flowing hyperostosis.
The imaging features of parosteal and periosteal osteosarcomas also differ markedly from melorheostosis because these tumors contain ossific mineralized matrix that is often irregular and not uniformly attenuated on radiographs and have high signal intensity on T2-weighted images [10].
Multiple osteochondromas can be differentiated by osteo medullary continuity.

Differential Diagnosis List

Final Diagnosis

Calvarial melorheostosis

URL:	https://www.eurorad.org/case/14185
DOI:	10.1594/EURORAD/CASE.14185
ISSN:	1563-4086