The co- existence of the innocent and the guilty: Sever's apophysitis and Eosinophilic Granuloma.

Clinical History

A 10-year-old child presented in the Child Health department with thoracic pain and mobility reduction of the right leg. The clinical and the laboratory examination revealed leukocytosis and eoshinophilia while the x-rays of the thoracic spine showed sphenoid distortion of the 8th vertebra without history of trauma (Fig1).

Imaging Findings

MRI of the thoracic spine was performed for further investigation. The 8th thoracic vertebra showed height loss with sphenoid distortion and pathologic signal (hypointense in T1, hyperintense in T2 and STIR- weighted images). Furthermore, there was a small amount of pathologic para-vertebral tissue. After intravenous gadolinium administration the 8th vertebra and the tissue showed markedly enhancement (Fig.2, 3). The imaging findings were compatible with "eosinophilic granuloma". The second step was bone scintigraphy in order to confirm the diagnosis by excluding other bone lesions. The bone scintigraphy showed increased radionuclide uptake of the 8th thoracic vertebra and the right calcaneus (Fig.4, 5). MRI examination of the right ankle was performed and demonstrated fragmentation and bone edema of the secondary ossification core of the right calcaneus, findings similar with "Sever's apophysitis" (Fig.6, 7).

Discussion

Langerhans cell histiocytosis (LCH) or histiocytosis X is characterized histologically, by a proliferation of dendritic cells resembling normal Langerhans cells. Clinical manifestations can vary from an isolated, non-progressive bony lesion (eosinophilic granuloma) to rapidly progressive multisystem involvement (Letterer-Siwe disease). LCH is not a neoplasm; it should be considered a proliferative lesion, possibly secondary to a defect in immunoregulation, producing destructive effects on the tissues in which such proliferation occurs. More than half of the patients younger than 2 years with disseminated LCH die of the disease, whereas unifocal LCH is usually self-limited. Age of onset varies according to the variety of LCH. Letterer-Siwe disease occurs predominantly in children younger than 2 years while localized eosinophilic granuloma(EG) occurs mostly frequently in 5-15 years. EG involves calvarium, ribs, mandible, long bones and spine. The classical lesion of the spine is the "vertebra plana". It consists of flattening of one vertebral body, with close apposition of the unaffected intervertebral disks. The residual vertebra is hypointense in T1-weighted images, hyperintense in T2-weighted images and enhances markedly with gadolinium injection. Sometimes there is extension of pathologic tissue to the ventral epidural space [1-3].
"Sever's apophysitis" in children is a self-limited situation related to an active growth spurt during 7-15 years of age, with male predominance. Furthermore, it is a common injury in young athletes, caused by running, jumping or repetitive microtraumas. The calcaneus bone contains both physeal and apophsyseal hyaline cartilage. The secondary ossification centre develops within this cartilage, usually with a multifocal appearance, duplicating the chondro-osseous transformation. Any type of injury can prevent this process which involves trabecular remodelling of primary and secondary spongiosa of metaphysis. Thus, the ossified nucleus appears with an increased fragmentation (reflecting mechanic demands during vulnerable periods) in children with Sever's apophysitis unlike the healthy population. MRI plays a significant role in the diagnostic procedure, showing the edematous changes within the calcaneal apophysis, possibly extending into the neighbour tuberosity. Plain radiography, ultrasonography and scintigraphy can exclude types of fractures and teninditis/ bursitis respectively. Differential diagnosis includes infectious or traumatic causes. Patients with calcaneous apophysitis do not have growth disturbance, so a repair process is not required. Common advice is rest and activity reduction [4-6].

Differential Diagnosis List

Final Diagnosis

Eosinophilic Granuloma and Sever's apophysitis

URL:	https://www.eurorad.org/case/14260
DOI:	10.1594/EURORAD/CASE.14260
ISSN:	1563-4086