Sinus histiocytosis with massive lymphadenopathy was first described by Rosai and Dorfman in 1969 [2]. The etiology of RDD remains unknown. RDD is hypothesized to occur secondary to an abnormal immunological response or an infectious factor. Recent studies suggested that infective agents like HHV-6 and Parvo B19 might be the causative factors [4]. RDD is characterized by massive, painless cervical lymphadenopathy variably associated with fever, leukocytosis, elevated erythrocyte sedimentation rate and weight loss. RDD of the nervous system has also been reported, and most cases involve the brain [5]. Spinal cord involvement such as intramedullary, intradural and extradural is apparently very rare in RDD [6–10]. Over 90 % of CNS RDD involves the leptomeninges. In neuroimaging it is seen as a dural-based, contrast-enhancing lesion. Thus, clinically and radiologically, the disease is thought to represent meningioma. In the first case, the lesions were confined to the intradural extramedullary of the cervical spine, which were provisionally diagnosed as multiple spinal meningiomas [7–9]. As in the present of the second case, isolated intradural RDD of the lumbosacral spine, extending into the right foramina at the S1/2 level is extremely rare.
The MRI features of isolated RDD were variable and could be misleading. In most cases, as in the present patients, the signals of the lesion ranged from iso- to hypointensity on T1 weighted images, and iso- to hyperintensity on T2 weighted images, and exhibits an intense and uniform enhancement after gadolinium administration [1, 3, 6–8, 10–13]. MR images are usually indistinguishable from other more common lesions in the extradural spinal space such as meningioma [7, 9, 14], lymphoma, and sarcoma [6]. RDD displayed neuroimaging features typical of meningioma with a dural tail. There are no pathognomonic radiographic marks to suggest a particular preoperative diagnosis. Therefore, the definitive diagnosis of RDD relies on histopathological examination, and the immunochemical analyses contribute to determining the final diagnosis [15].
The characteristic histopathological pattern of RDD is emperipolesis, which refers to phagocytosis of intact lymphocytes by macrophages. Large histiocytes of RDD are immunoreactive for S100 protein and CD68, but not for CD1a. This feature helps to distinguish from Langerhans cell histiocytosis, which is positive for CD1a [16].
The natural history of RDD has been reported to be benign with spontaneous remission. In some patients, however, rapid disease progression, multisystem involvement, and even fatal outcomes have been described [1, 2]. In case of persistent or progressive disease, a number of adjuvant therapies have been administered with variable success, including radiotherapy and chemotherapy with corticosteroids, 6-mercaptopurine and methotrexate [17]. Administration of steroids often resolve fever and reduce lymph node size. Radiation or chemotherapy has been shown to be beneficial in achieving complete remission in 33.3 % or 16.6 % of cases [18]. Resection of the lesions is an effective treatment choice to relieve spinal compression symptoms. There is no established systemic treatment protocol for RDD, since it is a rare disease presenting with different clinical features. Because the patients had improved neurological course after surgery, adjuvant treatments with chemotherapy or radiotherapy are unnecessary until disease progression is detected.
