Osteoma-Like Melorheostosis: a Rare Type of Skeletal Dysplasia Depicted on FDG PET/CT

Skeletal Radiology (2019) 48:1299–1303 https://doi.org/10.1007/s00256-019-3149-z

CASE REPORT

Osteoma-like melorheostosis: a rare type of skeletal dysplasia depicted on FDG PET/CT

Alain S. Abi-Ghanem1 & Karl Asmar1 & Fouad Boulos2 & Samar Muwakkit3

Received: 24 October 2018 /Revised: 3 January 2019 /Accepted: 3 January 2019 /Published online: 25 January 2019 # ISS 2019

Abstract Melorheostosis, also known as Leri’s disease, is a rare benign form of mesodermal mixed sclerosing bone dysplasia. We report the unusual case of a 14-year-old boy with melorheostosis in the lower extremity that went undiagnosed due to concurrent Ewing sarcoma in the opposite limb, confounding the findings for metastatic disease. The diagnosis was made on FDG PET/CT when the patient presented for post Ewing sarcoma treatment follow-up. The different types of melorheostosis as well as the challenge of diagnosing this rare entity are discussed in this report.

Keywords Melorheostosis . Bone dysplasia . FDG PET/CT . Sclerotome

Introduction the most prominent feature of melorheostosis in children and usually results in the incidental diagnosis on imaging [4]. Melorheostosis, also known as Leri’s disease, is a rare benign Clinical and radiological evidence are usually enough to diag- form of mesodermal mixed sclerosing bone dysplasia affect- nose the condition particularly since histological findings are ing both sexes equally with an incidence of 0.9 case per mil- nonspecific and can be misleading [1, 5]. lion [1, 2]. In adults, it is usually diagnosed incidentally We report the case of a pediatric patient with through imaging in patients complaining of chronic limb pain, melorheostosis in the lower extremity that went undiagnosed often with overlying skin changes described as tense, shiny, due to concurrent Ewing sarcoma in the opposite limb, con- erythematous, and sometimes covered with varices [1, 3]. In founding the findings for metastatic disease. the pediatric population, pain is rarely a dominant symptom and, when present, is usually mild. Limb length discrepancy is Case report

* Alain S. Abi-Ghanem The patient was a 14-year-old boy who presented to the emer- [email protected] gency department with left leg pain for the previous 4 months. Karl Asmar The patient had no other complaints and both social and fam- [email protected] ily histories were non-contributory. Fouad Boulos On physical exam, the patient had diffuse tenderness to [email protected] palpation along the left tibia as well as a palpable mass on the anteromedial aspect of the left proximal leg with a notice- Samar Muwakkit [email protected] able antalgic gait. The right leg was normal in appearance with no pain, tenderness, or skin changes. There was no limb length 1 Department of Radiology, American University of Beirut Medical discrepancy between either of the legs and routine laboratory Center, Riad El-Solh, PO Box 11-0236, Beirut 1107 2020, Lebanon exams were within normal limits. 2 Department of Pathology, American University of Beirut Medical Plain radiographs of the left leg showed a large soft tissue Center, Riad El-Solh, PO Box 11-0236, Beirut 1107 2020, Lebanon mass along the anterior medial aspect of the proximal to mid 3 Department of Pediatrics and Adolescent Medicine, American left tibial shaft with underlying irregular cortical erosion and University of Beirut Medical Center, Riad El-Solh, PO Box 11-0236, periosteal reaction suspicious for malignancy. Beirut 1107 2020, Lebanon 1300 Skeletal Radiol (2019) 48:1299–1303

MRI of the legs confirmed the aggressive nature of the mass in the left tibia. However, the right lower extremity showed extensive intramedullary mildly deforming enhancing lesions with low T1 and high T2 signal abnormality involving the right ischium, superior pubic ramus, acetabulum, femoral neck and shaft, tibia, talus, medial cuneiform and cuboid bone (Fig. 1). CT-guided biopsy of both tibial lesions was performed. The left tibial lesion showed malignant small round blue cell tumor compatible with Ewing sarcoma. The right tibial lesion showed dense irregular trabeculae of woven bone and fibroblastic stroma compatible with fibro-osseous disease such as fibrous dysplasia or low-grade osteosarcoma (Fig. 2). The patient was started on chemotherapy for Ewing sarcoma, namely a regimen of cyclophosphamide, vincristine, and Fig. 2 Histologic sections of right proximal tibia show dense irregular doxorubicin every 2 weeks for 4 months. trabeculae of woven bone (asterisk) separated by a fibroblastic stroma Upon follow-up, MRI showed good response to treatment (arrowhead) (H&E, ×100) in the left leg. However, the right lower extremity lesions were stable in appearance. This raised the suspicious of a benign lesions were predominant in the tibia. They also involved process, independent from the sarcoma in the contralateral leg. the intramedullary canal and caused endosteal scalloping FDG PET/CT was performed for restaging prior to under- and deformation. The overall findings were suspicious for a going surgery to the left leg sarcoma. The lesions seen on MRI mesenchymal dysplasia. The distribution of the bony lesions in the right lower extremity were intensely FDG-avid, mildly along a sclerotome, in this case L5, and the absence of sur- sclerotic with ground-glass matrix extending from the right rounding soft tissue abnormality were highly suggestive of acetabulum to the right distal foot, along the first ray. The melorheostosis (Fig. 3).

Fig. 1 Lower extremity MRI of a 14-year-old boy presenting with melorheostosis in the right leg and Ewing sarcoma in the left leg. There are extensive intramedullary well-defined mildly deforming and heterogeneously enhancing lesions in the right tibia on T1- post contrast sequences (a and d), with low signal abnormality on T1 (c) and T2-weighted sequences (e). In the left leg, there is an ill-defined intramedullary lesion in the proximal tibia (b) with low-to-intermediate T1- weighted (c) and high T2- weighted (e) signal abnormality. There is also cortical thinning with periosteal elevation and large enhancing soft tissue component (b) Skeletal Radiol (2019) 48:1299–1303 1301

Fig. 3 Whole-body FDG PET/CT after chemotherapy of a 14-year-old markedly responded to chemotherapy. b, c Axial fused PET/CT and CT boy presenting with melorheostosis in the right lower extremity and images at the level of the right mid tibia showing disease involvement Ewing sarcoma in the left proximal tibia. a Maximum intensity projection with SUVmax 15.4. On CT, the right lesions are well circumscribed with image showing intensely FDG-avid heterogenous lesions in the right ground-glass appearance (asterisk) and cortical thinning (arrowhead)(c). lower extremity extending from the right acetabulum down to the medial d Sagittal fused PET/CT image at the level of the right tibia showing aspect of the right foot. The Ewing sarcoma in the left proximal tibia has disease involvement

Upon further review of the pathology slides and putting meaning flowing and Bostos^ meaning bone. Although the together the clinical and imaging findings, the diagnosis of name reflects the classic type of the disease, the osteoma- melorheostosis in the right lower extremity was confirmed. like type seems to be the most frequently encountered [7, 8]. The patient underwent resection of the left proximal tibial Melorheostosis can affect any body part. It can be mass, bone grafting, and open reduction internal fixation with monostotic or polyostotic in distribution. It can also affect plates and screws. His last follow-up PET/CT 10 months after one limb (monomelic) or several limbs (polymelic) (Fig. 4). initial presentation showed post-surgical changes in the left The diagnosis is usually attained through clinical assess- proximal to mid tibia while his right lower extremity FDG- ment and imaging because of its distinctive radiological fea- avid melorheostosis remained unchanged. tures, particularly on bone scans. The classic radiographic appearance is that of a flowing cortical hyperostosis along one side of the shaft of long bones resembling melted wax Discussion flowing down the side of a candle. This is mostly in adults. The osteoma-like type tends to present with hyperostosis lo- cated either on the outer aspect or the inner aspect of the long Several types of melorheostosis have been described: classic, bone. This is commonly seen in children where osteoma-like, myositis ossificans-like, osteopathia striata-like, melorheostosis presents as diffuse or localized patchy endos- and mixed [6]. The frequency of occurrence of each type is not teal sclerosis. The osteopathia striata-like pattern presents with very clear but some case series have reported similar frequen- dense hyperostotic striation near the inner side of the cortex. cies for all types except for the myositis ossificans-like type Unlike osteopathia striata, melorheostosis has unilateral stria- which seems to be less frequent. In fact, in a case series of 23 tions that tend to be much larger and much broader. The myo- patients, seven osteoma-like cases (30%), five classic cases sitis ossificans-like type presents with ossifications in the soft (22%), six osteopathia striata-like cases (26%), four mixed tissues with a nodular arrangement lacking a lamellar appear- cases (17%), and only one myositis ossificans-like case (4%) ance. As melorheostosis progresses, endosteal hyperostosis were reported [7]. The etymology of Bmelorheostosis^ is de- may occur, which results in obliteration of the medullary rived from the Greek terms Bmelos^, meaning limb, Brhein^ 1302 Skeletal Radiol (2019) 48:1299–1303

Fig. 4 a Schematic representation of the distribution of melorheostosis review of literature (313 cases). Journal of Musculoskeletal Research. throughout the skeleton. The lower limb is the most commonly affected 2012 Jul 9;15(2)]. b Schematic depicting the upper and lower limb followed by the upper limb and the spine. The rib cage and craniofacial sclerotomes, adapted from Murray et al. [Murray RO, McCredie J. bones are the least commonly affected. This schematic is adapted from Melorheostosis and the sclerotomes: a radiological correlation. Skeletal data presented by Artner et al. [Artner J, Cakir B, Wernerus D, Reichel H, Radiology. 1979 Jun 6;4(2):57–71] Nelitz M. Melorheostosis: current concepts in diagnosis and treatment. A cavity. The appearance of bony overgrowth especially around left leg responded to chemotherapy, while the right leg pathol- the hip may resemble osteochondromas [6, 8]. ogy remained stable. This was thought to represent polyostotic On imaging, the differential diagnosis of melorheostosis is fibrous dysplasia on follow-up MRI. In fact, fibrous dysplasia wide and includes parosteal osteosarcoma, myositis lesions are classically intramedullary, expansile, and well de- ossificans, calcified hematoma, chronic osteomyelitis, fined, as in our patient’s case. However, cortical thinning and osteopoikilosis, and infantile cortical hyperostosis [1, 5]. disruption, which were seen in our patient, are not character- When melorheostosis occurs with vascular or skin abnormal- istic of fibrous dysplasia where there is always a smooth cor- ities, then the differential diagnosis should include syndromes tical contour even when endosteal scalloping is reported [9]. such as Maffucci syndrome, Klippel–Trenaunay syndrome, FDG PET/CT gave the clue for the diagnosis of McCune–Albright syndrome and other mosaic/localized dis- melorheostosis by highlighting the sclerotomal distribution. orders [5]. The disease in the right lower extremity was FDG-avid and In our case, we encountered a monomelic polyostotic followed the distribution of the L5 sclerotome along the first osteoma-like melorheostosis in the right lower extremity of ray. Review of the pathology slides, in conjunction with the an adolescent, which coincidentally occurred with Ewing sar- radiological images, showed dense irregular trabeculae of wo- coma in the opposite lower extremity. The melorheostosis ven bone devoid of osteoblastic rimming and separated by a remained undiagnosed until the patient presented for a post- fibroblastic stroma, supporting the diagnosis of chemotherapy FDG PET/CT despite the multiple imaging melorheostosis [10]. modalities he had already been subjected to. The fact that Melorheostosis has been described in association with mes- the patient presented with complaints related to his left lower enchymal tumors such as glomus tumors, giant cell granulo- extremity tumor rather than symptoms associated with ma, arteriovenous malformations, and hemangiomas [8, 11], melorheostosis in his right lower extremity contributed to and some case reports have even reported osteosarcoma the delay in diagnosis. 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