Granulocytic sarcoma of the brain in an adult with chronic myeloid leukaemia

Clinical History

A 21-year-old man presented to the emergency department with headache and vomiting. The patient was diagnosed with chronic myeloid leukaemia 9 months before with early progression to blastic phase 3 months later, achieving haematologic and cytogenetic remission with chemotherapy plus imatinib. So allogeneic bone marrow transplantation was proposed.

Imaging Findings

On the unenhanced brain CT, multiple supratentorial hyperdense intraaxial masses surrounded by oedema were identified (Fig. 1.a), with intense homogeneous enhancement after contrast administration (Fig. 1.b).
On MR imaging, T2-weighted and T2-FLAIR images showed multiple hypointense lesions at the corticomedullary junction (Fig. 2a and 2b). The lesions were hyperintense in diffusion-weighted imaging and hypointense in ADC map, characterizing restricted diffusion, with perilesional vasogenic oedema (Fig 2c). On T1-weighted images the lesions corresponded to hypointense areas (Fig. 3a) with homogeneous enhancement after contrast administration (Fig. 3b).
The CT scan performed a week after intrathecal chemotherapy showed partial regression of the lesions (Fig. 4).

Discussion

Granulocytic sarcoma (GS) is a rare solid tumour composed of immature granulocytes that usually occurs with systemic leukaemia [1]. Most cases arise in acute myeloid leukaemia (3-7% of such patients), but myelodisplasic diseases and chronic leukaemia (CL) can also ensue [1, 2].
This tumour is also known as chloroma due to the green colour caused by a high myeloperoxidase content, but the term GS is preferred since up to 30% of tumours are not green [1, 2].
GS is typically seen in children with almost 60% occurring in individuals younger than 15 years. There is no recognized gender predilection.
GS can arise anywhere, with a predilection for bone, lymph nodes and skin or soft tissues [3]. Central nervous system involvement is rare, occurring in only 5% to 14% of cases [3, 4]. It is believed that leukaemic cells migrate from the bone marrow through harversian canals, the periostium and the dura to the intracraneal space. Posterior infiltration of the brain where the pial–glial barrier has been disrupted then allow the tumour to become intraaxial [4, 5].
Brain involvement presents with focal signs from local mass effect and headache from haemorrhage.
On unenhanced CT, GS is seen as iso- or hyperdense mass [5]. Uniform contrast enhancement is usually present [5]. Central hypodense areas probably corresponding to tumour necrosis have also been described [5, 6].
On MR imaging, granulocytic sarcomas are typically iso to slightly hypointense on T1-weighted imaging and heterogeneously hyper to isointense on T2-weighted imaging relative to brain tissue [4, 5]. The high concentration of myeloperoxidase (an iron-containing enzyme) in the tumour is probably responsible for its low signal intensity on T2-weighted sequences [4]. Uniform enhancement is usually noted [4, 5]. Hyperintensity in diffusion-weighted images with corresponding hypointensity in ADC maps, characterizing restricted diffusion, is related to the high cellularity [7].
Still, the best diagnostic clue is a homogeneous enhancing tumour(s) in patients with known or suspected myeloproliferative disorder.
GS in setting of CL as in ours cases implies blastic transformation and is a poor prognostic sign. Prompt diagnosis will facilitate appropriate treatment and disease control. Various treatment strategies are described in the literature, mostly systemic or intrathecal chemotherapy, irradiation or surgery [8].
Our patient received intratechal chemoterapy and control CT performed 1 month lather was indicative of tumour regression.

Differential Diagnosis List

Final Diagnosis

Granulocytic sarcoma

URL:	https://www.eurorad.org/case/13625
DOI:	10.1594/EURORAD/CASE.13625
ISSN:	1563-4086