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Neuroradiology Case of the Week

Case 166

David Tuttle, Ajay Malhotra, MD, and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: A 14-year-old male presented with a two week history of headaches, lump over left temple, and new periorbital swelling and redness.

Radiological Findings:  Axial and coronal CT images (Figs. 1A-C) demonstrate a homogeneous mass in the posterolateral aspect of the left retro-orbital space. There is associated punched-out bony lesion involving the left orbital wall in the greater sphenoid wing. The mass extends into the posterolateral retro-orbital space, displacing the left lateral rectus muscle and optical nerve medially. The lesion is also seen extending into the infratemporal fossa down to the region of the pterygo- palatine fossa without involvement of the pterygoid plate.  MR images (Figs. 2A-without contrast and B-with contrast) demonstrate these findings well.
     The patient underwent excisional biopsy of the left orbital mass which revealed Birbeck Granules-pathognomic for eosinophilic granuloma. Subsequently radiation therapy was given for the orbital lesion.
     Post-treatment follow-up imaging at 4 months (Fig. 3) showed decrease in the size of this mass and MR at 1 year after completion of treatment (Fig. 4) showed no abnormal soft tissue enhancing mass in the left orbital wall, suggesting complete resolution. Tc99MDP scans at 1 year follow-up did not show any increased uptake in the left orbital wall.

Diagnosis: Langerhans cell histiocytosis (Eosinophilic Granuloma)

Discussion: Histiocytoses are a group of disorders caused by proliferation of bone marrow derived mononuclear phagocytic cells (histiocytes).  Langerhans cell histiocytosis (LHC) is a dendritic cell-related histiocytosis that may involve bone, skin, or may present as multisystem disease.
     LHC is mostly a childhood disorder with a peak diagnosis between 1 and 3 years.  Incidence is estimated between 0.54 and 0.9 cases per 100,000 children per year, and is more common in boys than girls (1.2-2:1).  Some believe that the disease is under diagnosed as bone lesions may be asymptomatic or mistaken for trauma.  LHC is usually sporadic.  However, 1% of patients have a family history of LHC, suggesting a genetic tendency.  The etiology of the disease is unknown and there are no well accepted environmental risk factors. 
     Bone is the most commonly affected organ in LHC, and single or multiple sites may be involved.  Lesions are typically osteolytic with surrounding sclerosis and are most often found in the skull, mandible, vertebrae, ribs, pelvis, and long bones.  The patient may be asymptomatic or may suffer pain, fractures, and deformities.
     Initial imaging is performed to evaluate the extent of the disease, with further imaging performed to follow disease progression or resolution.  In bone lesions plain film is used as the initial study.  Lesions appear lytic with poorly defined borders, with or without sclerosis.  More aggressive lesions cause more bone destruction with a moth eaten bone appearance.  In the skull, lesions are oval or round with well-defined margins.  CT or MRI are useful in evaluating soft tissue involvement as well as lesions in the face and skull base difficult to define by plain radiographs.  Scintigraphy is used at diagnosis and follow-up to locate active disease sites.
     The differential diagnosis includes Ewing sarcoma, lymphoma, leukemia, metastasis, rhabdomyosarcoma and osteomyelitis.  Diagnosis is made on pathological examination.  Light microscopy with H&E stain may reveal morphology consistent with granulomatous disease with histiocytes present.  Definitive diagnosis is made by immunoassaying for CD1a or with visualization of pathognomonic Birbeck granules on electron microscopy. 
     Treatment of bone lesions may involve indomethacin, steroids, curettage, or radiation.  If the patient is asymptomatic and there is little risk of permanent sequelae, no intervention is required as lesions may resolve spontaneously.  Treatment for bone lesions is necessary when the lesions involves a weight bearing bone or surrounds a vital structure such as the optic nerve or spinal cord.  Prognosis is very good for lesions involving only bone.

References:

1. Henter JI, Tondini C, Pritchard J. Histiocyte disorders. Crit Rev Oncol Hematol. 2004 May;50(2):157-74. [Medline]
2. Meyer JS, De Camargo B. The role of radiology in the diagnosis and follow-up of Langerhans cell histiocytosis. Hematol Oncol Clin North Am. 1998 Apr;12(2):307-26. [Medline]
3. Azouz EM, Saigal G, Rodriguez MM, Podda A. Langerhans' cell histiocytosis: pathology, imaging and treatment of skeletal involvement. Pediatr Radiol. 2005 Feb;35(2):103-15. Epub 2004 Jul 28. [Medline]
4. Arico M, Egeler RM. Clinical aspects of Langerhans cell histiocytosis. Hematol Oncol Clin North Am. 1998 Apr;12(2):247-58. [Medline]