Radiological Category Neuroradiology Principal Modality 1 CT Principal

Radiological Category: Neuroradiology Principal Modality (1): CT Principal Modality (2): none Case Report # 761 Submitted by: Megan Kalambo, M. D. Faculty reviewer: Emilio Supsupin Jr. , M. D. and Anuradha Rao, M. D. The University of Texas Medical School at Houston Date accepted: 31 January, 2011

Case History 49 year old diabetic male, no recent intervention. Additional history withheld.

Radiological Presentations AXIAL CT IMAGE SOFT TISSUE WINDOWS AXIAL CT BONE WINDOWS

Radiological Presentations CORONAL CT IMAGE BONE WINDOWS SAGITTAL CT IMAGE BONE WINDOWS

Test Your Diagnosis Which one of the following is your choice for the appropriate diagnosis? After your selection, go to next page. • Arachnoiditis Ossificans • Neuritis Ossificans • Sacral Osteoid Osteoma • Sacrococcygeal Chordoma

Findings and Differentials Findings: Axial soft tissue and bone window CT images through the pelvis demonstrate homogeneous hyperdensity in the region of the right S 2 nerve root. The surrounding soft tissues and visualized bowel are unremarkable. Sagittal and Coronal CT images in bone windows through the pelvis confirm concentric heterotopic ossification of the right S 2 nerve root. The visualized lumbar and sacral vertebral bodies and bony pelvis are intact. There is no neuroforaminal widening. Differentials: • Arachnoiditis Ossificans • Neuritis Ossificans • Sacral osteoid osteoma • Sacrococcygeal Chordoma

Discussion Differential considerations for hyperdense calcifications in the lumbosacral region: Sacral osteoid osteoma is characterized by a radiolucent lesion surrounded by perifocal sclerosis. The tumor is typically called a “nidus” to distinguish it from the surrounding reactive and sclerotic bone. Central calcification may be observed within the osteolytic nidus. These tumors typically arise from the articular process of S 1. In neuritis ossificans, there is homogenous concentric calcification of a peripheral nerve root without neuroforaminal narrowing. Imaging findings characteristic of sacral chordoma involve a sacral soft tissue mass with associated lytic expansion of the sacrum and amorphous intralesional calcifications. The majority of chordomas arise from the sacrococcygeal region, characteristically in the fourth and fifth sacral segments. Arachnoiditis ossificans is characterized by the presence of small calcifications or ossifications in the leptomeninges. In the lumbosacral region, they are often intradural and adjacent to the nerve roots. The ossification can appear thin and linear, or globular and masslike.

Diagnosis Neuritis Ossificans of the Right S 2 Nerve Root, Given the presence of homogenous heterotopic ossification of the right S 2 nerve root, in the absence of recent myelogram, a sacral soft tissue mass, bony destruction, or widening of the neural foramina, neuritis ossificans is the most likely diagnosis.

Neuritis Ossificans is a rare reactive nerve disease reported to affect systemic peripheral nerves. The process of ossification is felt to be intraneural and encasing, rather than directly involving the nerve fascicles. Cases have been reported involving cranial, common peroneal, median, digital and sciatic nerves. Neuritis ossificans has a broad clinical spectrum ranging from an asymptomatic incidental finding to pain and numbness along the distribution of the involved nerve root. Consisting of a central fibroblastic core, an intervening zone of osteoid production, and a peripheral layer of ossification, the histologic pattern is remarkably similar to that of myositis ossificans. Given the occurrence in peripheral nerves and similar histologic properties to myositis ossificans, it has been suggested that trauma may play a role in its pathogenesis.

Teaching Points: Neuritis Ossificans Calcified right S 2 nerve root. No neuroforaminal widening , presacral mass or bony destruction.

Diagnosis Neuritis Ossificans of the Right S 2 Nerve Root

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