Radiologic Findings in a Patient with Frontal Parafalcine Dendritic Cell Histiocytoma

Discussion

We present the radiologic findings of a patient with biopsy-proven dendritic cell histiocytoma presenting as a single intracranial extra-axial mass with no systemic disease. Two lines of cellular differentiation for histiocytes have been described in the literature with important functional, morphologic, and phenotypic similarities: the dendritic cells and the cells derived from the macrophage-monocyte series. Immunophenotyping is particularly useful to differentiate macrophages that are characteristically phagocytic cells with prevalent antigen-processing functions from dendritic cells with predominately antigen-presenting capabilities.^1,2

The World Health Organization classifies this tumor as a solitary histiocytoma with various dendritic cell phenotypes.³ These phenotypes are illustrated in the Table.^4,5 Although most often cutaneous,^6–8 these lesions can develop elsewhere. They have been described in the cervical lymph nodes, the mediastinum, the spleen, the axilla, the oral cavity, the thyroid gland, the peripancreatic soft tissues, and the spine.^9–12 Cases of juvenile xanthogranulomas (JXG), which are derived from dermal dendrocytes and benign fibrous histiocytomas (BFH), tumors composed of fibroblastic and histiocytic cells, have been described in the central nervous system.^13,14 A careful review of the literature revealed no similar cases of supratentorial dural-based dendritic cell histiocytoma other than 12 such lesions reported briefly by Jaffe and Favara in abstract form.¹⁵ In 4 of those patients, the lesion involved dura and/or adjacent bone.

The radiologic findings of this extra-axial tumor are nonspecific. On noncontrast brain CT, the mass appeared nodular and hyperattenuated extending into the superior sagittal sinus. The lesion enhanced avidly. It was relatively dark on T2-weighted scans. In addition, increased signal intensity on diffusion-weighted images with corresponding decreased signal intensity on an apparent diffusion coefficient map indicated some restricted diffusion, probably reflecting hypercellularity. Such features suggest an aggressive lesion without pointing to a specific diagnosis.

Until further characterizing features of these types of tumors are delineated with MR spectroscopy and/or positron-emission tomography, the differential diagnostic possibilities remain wide. An aggressive meningioma should be suggested at first even in a patient of this age, though most meningiomas occur in the middle decades of life. A hemangiopericytoma tends to occur in younger patients than those with typical meningiomas and more often in men,¹⁶ but is still rare in children. Dural metastases, lymphoma, amyloidoma, and plasmacytomas may be suggested by a history of HIV infection, systemic lymphoma, myeloma, or a primary malignancy. Also, granulomatous diseases, such as sarcoidosis, tuberculosis, or fungal infection, should be suspected when compatible systemic symptoms are present.¹⁷ Rare tumors such as JXG and BFH with dural attachment should be considered, though they are uncommon without systemic involvement and/or cutaneous and subcutaneous soft tissue lesions.^13,14

Clinically, dendritic cell histiocytomas, though biologically benign, have the capacity to recur and progress, especially if incompletely resected, as was the case with our patient. Radiation therapy after complete surgical removal may prevent recurrence. A careful follow-up is essential, because these lesions can predict more systemic and serious histiocytic processes.^3,13