Teaching Case

A 22-year-old male patient with known sickle cell disease presented with general malaise, right jaw pain and trismus. Clinical assessment revealed right lower lip paraesthesia, oral opening limited to 0.5cm and raised inflammatory markers. A working diagnosis of sickle cell crisis was made, with trismus of unknown origin.

A contrast enhanced MRI confirmed the absence of a deep space soft tissue or upper aerodigestive tract abnormality. The post-contrast sequence did however reveal a very shallow, rim enhancing pocket of fluid abutting the medial cortex of the ascending mandibular rami bilaterally. Normal signal was returned from the adjacent medullary bone on all sequences. CT to assess for direct underlying bone involvement or abnormality and rule out atypical osteomyelitis was normal, and showed no medullary sclerosis or cortical breach. Conservative management was initiated and the trismus resolved. At five weeks, a follow-up MRI demonstrated resolution of the peripherally enhancing pockets, but new high T2-signal from the adjacent medullary bone without enhancement, suggestive of bone oedema.

Sickle cell disease is an inherited autosomal recessive disease. It is a type of haemoglobinopathy, where a mutation in the HBB gene causes production of abnormally shaped red blood cells (RBC). These RBC contain haemoglobin S rather than normal adult haemoglobin A, resulting in a loss of elasticity and deformation of the RBC to a sickle shape. The deformed RBCs are susceptible to haemolyse leading to the characteristic haemolytic anaemia seen clinically. In low-oxygen saturation,  RBCs start to aggregate leading to microvascular occlusion. Resultant local hypoxia leads to marrow infarction which extends to the overlying cortex. Here; sequestrated erythrocytes and serum are extravasated into the subperiosteal space [1]. The subsequent inflammatory response leads to white-cell activation and accumulation resulting, as in the case presented here, in altered signal intensity at the periosteum [2], and peripherally enhancing subperiosteal collections [3]. Subperiosteal haemorrhage and collection formation are widely recognised sequelae of the disease process [1,2,3]. Other craniofacial manifestations of the disease include orbital infarction [4] and wide-ranging dental presentations [5].

This case illustrates the early imaging findings of sickle cell related vaso-occlusive bone infarcts. The initial MRI examination demonstrates the presence of reactive subperiosteal fluid accumulation bilaterally in the mandibular ramus, in response to early underlying ischaemia/infarction. The delayed MRI demonstrates resolution of the fluid collections, following conservative treatment with residual underlying bone oedema. The CT proves the absence of any underlying bone sclerosis or cortical breach at initial presentation. It is our belief that the subperiosteal fluid accumulations were causative of the patients’ trismus, which resolved alongside the radiologically proven resolution of the fluid accumulations. Neuropathy of the mental nerve is a recognised finding in vaso-occlusive crisis [6]. This patient reported only unilateral paraesthesia in the region of the mental nerve and we believe that this was related to the ipsilateral fluid collection. Given that mental paraesthesia is a recognised finding in vaso-occlusive crisis, care should be taken to check for a similar radiological appearance when early imaging is undertaken in this condition. As described, the finding of subperiosteal fluid collections which resolve, then subsequent development of bone oedema at delayed imaging corresponds to the pathological progression of this condition. Similar findings are likely to be demonstrated in other patients imaged early in the course of sickle cell related vaso-occlusive crisis. Hence awareness of the radiological presentation is essential to facilitate timely diagnosis.

Written patient consent for this case was waived by the Editorial Board. Patient data may have been modified to ensure patient anonymity.