Melorheostosis Incidentally Detected during Staging of Colon Carcinoma

Abstract

A 32-year-old female patient presented with progressive abdominal pain and constipation for 3 years and frequent defecation with intermittent rectal bleeding for 2 years. She had no prior similar symptoms or family history of malignancy. Colonoscopy revealed a circumferential, obstructing ulceroproliferative mass in the descending colon, and histopathologic analysis confirmed moderately differentiated adenocarcinoma.

Contrast-enhanced chest CT demonstrated heterogeneously enhancing mural thickening with mucosal irregularity in the descending colon, along with enlarged pericolic lymph nodes and fat stranding. Incidentally, CT also showed multiple sclerotic lesions involving several left-sided ribs and thoracic vertebrae (Figure), characterized by dense cortical hyperostosis with irregular undulating borders and combined periosteal and endosteal thickening. Although osteoblastic metastases were initially considered, comparison with prior chest radiographs from 2019 (acquired during evaluation for respiratory infection) demonstrated stability of these lesions over a 2-year period, consistent with melorheostosis. Laboratory evaluation showed normal alkaline phosphatase (78 U/L; reference range, 44–147 U/L) and serum calcium (9.2 mg/dL; reference range, 8.5–10.5 mg/dL), supporting a benign etiology.

Contrast-enhanced chest CT in a 32-year-old female patient undergoing staging for colon adenocarcinoma shows characteristics of melorheostosis. (A) Axial contrast-enhanced CT image shows irregular circumferential mural thickening of the descending colon with pericolic fat stranding and lymphadenopathy, consistent with malignancy. (B, C) Axial and sagittal CT images show dense cortical thickening with irregular, flowing hyperostosis involving the left-sided ribs and thoracic vertebrae, without soft-tissue mass or aggressive periosteal reaction, characteristic of melorheostosis. (D) Volume-rendered image highlights undulating cortical hyperostosis along the involved ribs. Lesions were unchanged on prior radiographs, supporting a benign etiology.

Melorheostosis is a rare, sporadic sclerosing bone dysplasia characterized by cortical hyperostosis (1). Although appendicular involvement is most common, axial skeletal disease—including rib and vertebral involvement—has also been reported (2). The classic radiographic appearance resembles “dripping candle wax,” reflecting flowing cortical thickening along one side of the bone (3). Five morphologic patterns are described: classic dripping candle wax, endosteal osteoma-like, myositis ossificans–like, osteopathia striata–like, and mixed (4); our patient exhibited the classic variant. Bone metastases from colorectal carcinoma are uncommon (<10% of cases) and are predominantly lytic rather than blastic. When blastic metastases occur, they typically demonstrate mixed lytic-blastic patterns, aggressive periosteal reaction, soft-tissue mass, and elevated alkaline phosphatase—features absent in this patient. The diagnosis of melorheostosis was established based on characteristic imaging features, 2-year stability, normal bone turnover markers, and absence of aggressive findings, obviating the need for PET/CT or biopsy. Although histologic confirmation was not obtained, melorheostosis shows dense lamellar bone with irregular Haversian systems and abnormal osteocyte distribution without cytologic atypia, in contrast to metastatic colorectal carcinoma, which demonstrates malignant glandular epithelium (CK20+, CDX2+) surrounded by reactive woven bone. In oncology patients, melorheostosis may mimic osteoblastic metastases; correlation with prior imaging and recognition of characteristic cortical patterns are critical to avoid misdiagnosis and inappropriate upstaging.

The patient underwent laparoscopic-assisted anterior resection for the primary tumor, and the osseous lesions were managed nonoperatively with follow-up. Management with regular surveillance is appropriate for asymptomatic lesions; surgical intervention may be considered for severe refractory pain, significant limb length discrepancy, or joint contractures causing functional impairment.

Keywords: Skeletal-Axial, CT, Oncology, Thorax

Disclosures of conflicts of interest

Please see ICMJE form(s) for author conflicts of interest. These have been provided as supplemental materials.