Intracranial Myeloid Sarcoma

A 75-year-old white female presents to the emergency department with fever and fatigue. Her medical history is notable for acute myeloid leukaemia on multi-regimen chemotherapy and marrow-stimulating agents. Physical exam is unremarkable. WBC count is 0.03. CSF WBC count of is 2914. CSF flow cytometry showed myeloblasts.

Axial non-contrast CT at the level of the basal ganglia demonstrates a hyperattenuating lesion in the left basal ganglia with mild surrounding vasogenic oedema. Axial post-contrast CT at the same level demonstrates intense homogeneous enhancement of the lesion and leptomeningeal enhancement along the temporal lobes and cerebellar folia. Axial MR susceptibility weighted imaging at the level of the basal ganglia demonstrates no signal dropout in the lesion and the ADC map demonstrates restricted diffusion. Additionally noted is extensive leptomeningeal enhancement.

Cranial myeloid sarcoma, also known as granulocytic sarcoma or chloroma (historically), is a solid tumour composed of extramedullary myeloid precursor cell deposits in the setting of a myeloproliferative disorder, most commonly acute myeloid leukaemia [1,2,3]. Myeloid sarcoma can occur anywhere in the body, for instance, in the central nervous system, either intra or extra-axial [2,3]. Although usually asymptomatic, some patients may present with nonspecific symptoms related to mass effect [1,3]. The pediatric population is involved in approximately 60% of the cases and there is no sex predilection [1]. Overall, the reported incidence is 2.5-9% in those with acute myeloid leukaemia; specifically, intra-axial CNS involvement is extremely rare [1,3]. 

On non-contrast CT, cranial myeloid sarcoma presents as a solid hyperattenuating lesion due to densely packed cells. Post-contrast images demonstrate intense enhancement. On MR, these lesions are T1 isointense/hypointense and T2 mildly heterogeneously hyperintense [3]. Again, post-contrast images demonstrate avid homogeneous enhancement, although ring enhancement may be seen in the setting of large lesions or during treatment due to central necrosis [2,3]. Diffusion-weighted images will show restricted diffusion in the lesion [2]. Tissue sampling confirms diagnosis; however, acute myeloid leukaemia and classical imaging findings obviates this and thus tissue sampling should be reserved for indeterminates cases [1,3].  

Prognosis of myeloid sarcoma is uncertain and the overall survival rate of acute myeloid leukaemia may be unaffected. Treatment entails treating the source lymphoproliferative disorder with systemic chemotherapy. In certain cases, localized radiotherapy or surgery can be performed to relieve any mass effect [1].

All patient data have been completely anonymized throughout the entire manuscript and related files.