AJR 2003; 180:78-80
© American Roentgen Ray Society
CT Changes of an Intracranial Granulocytic Sarcoma on Short-Term Follow-Up
Boris Nikolic1,2,
Frank Feigenbaum3,
Suhny Abbara1,
Robert L. Martuza3,4 and
Dieter Schellinger1
1 Department of Diagnostic Radiology, Georgetown University Hospital and Medstar
Health, 3800 Reservoir Rd. N.W., Washington, DC 20007.
2 Present address: Department of Radiology, Emory University, 1365 Clifton Rd.,
N.E., Atlanta, GA 30322.
3 Department of Neurosurgery, Georgetown University, Washington, DC 20007.
4 Present address: Department of Neurosurgery, Massachusetts General Hospital,
55 Fruit St., Boston, MA 02114.
Received February 1, 2002;
accepted after revision July 1, 2002.
Address correspondence to B. Nikolic.
Introduction
Granulocytic sarcoma is a focal tumor composed of neoplastic granulocytic
cells that is found in approximately 3-7% of patients with myelogenous
leukemia [1]. Considered to be
leukemia-related, granulocytic sarcoma takes the form of a solid mass, or
granulocytic germinal center, causing locally compressive symptoms
[1]. Bone, periosteum, soft
tissue, lymph nodes, and skin are most often involved
[2].
Central nervous system manifestations of granulocytic sarcoma are extremely
rare. Therefore, the addition to the literature of this case and its imaging
peculiarities seems appropriate.
We describe a patient with an intracranial granulocytic sarcoma in whom
initial MR imaging and serial unenhanced CT were performed. Serial imaging was
performed over a 3-week period. Corticosteroid therapy was administered during
the first 5 days. The short-term follow-up CT scans revealed dramatic and
extensive interval changes in the tissue texture of the granulocytic sarcoma
after the initiation of corticosteroid therapy, which to our knowledge has not
previously been reported.
Case Report
A 45-year-old man who had been previously diagnosed with acute myelogenous
leukemia was admitted to the hospital after head trauma. MR imaging was
performed at admission and revealed a large, heterogeneous, strongly and
uniformly enhancing, dural-based left frontal lesion with substantial mass
effect (Fig. 1A). Enhancement
was noted along the parietal dura, which is consistent with dural involvement
of this lesion (Fig. 1A).
Meningioma was initially considered but later excluded because MR imaging from
1 month earlier showed normal findings in the area of the lesion. With the
patient's clinical history of acute myelogenous leukemia, the most likely
radiologic diagnosis was that of an intracranial granulocytic sarcoma. Less
likely considerations were sarcoidosis and metastatic disease.
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Fig. 1A. —45-year-old man with acute myelogenous leukemia. Axial
contrast-enhanced T1-weighted MR image (TR/first-echo TE, second-echo TE,
600.0/14.0, 1) shows uniformly enhancing left frontal mass. Note mass effect
with midline shift. Large area of encephalomalacia in right occipital region
is consistent with patient's history of intracerebral hematoma.
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On an unenhanced CT scan that was obtained 2 days later, the mass was again
heterogeneous but predominantly hyperdense, and no significant interval change
in size or morphology was seen (Fig.
1B).
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Fig. 1B. —45-year-old man with acute myelogenous leukemia. Unenhanced
CT scan obtained at admission shows left frontal hyperdense mass with
surrounding edema (white arrows) and internal hypodense areas
(black arrows), which likely represent necrosis.
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A second CT scan was performed 5 days later and showed hypoattenuation of
the previously hyperdense lesion (Fig.
1C). The rapid change in attenuation was interpreted as tumor
necrosis and liquefaction, either spontaneous or as a result of
corticosteroid-induced tissue changes.
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Fig. 1C. —45-year-old man with acute myelogenous leukemia. Unenhanced
CT scan obtained 5 days after B shows extensive attenuation changes.
Mass is now predominantly hypodense; mass effect is unchanged.
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Three days later, the patient became increasingly somnolent. A decision was
made to perform an open biopsy despite the patient's severe thrombocytopenia.
Open biopsy was chosen instead of a closed stereotactic procedure in order to
allow direct visualization and coagulation of tissues. Direct visualization
during the surgery confirmed the imaging expression that the mass was
extraaxial. Notably, after part of the tumor was sampled for pathologic
analysis, the dura was seen approximately 1 cm deep in relation to the removal
site, suggesting epidural as well as subdural tumor extension. The biopsy
specimen was histologically consistent with granulocytic sarcoma. Because of
the known sensitivity of this lesion to radiation and chemotherapy, and
because of the risk of hemorrhage of a large craniotomy, the decision was made
to proceed with nonoperative treatment.
On the basis of these findings, a course of left frontal, external beam
radiotherapy was administered. The patient's neurologic condition stabilized,
and a final CT scan 15 days later (Fig.
1D) revealed a decrease in the size of the mass but no significant
interval change in attenuation characteristics when compared with the most
recent study.
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Fig. 1D. —45-year-old man with acute myelogenous leukemia. Unenhanced
CT scan obtained 15 days after external beam radiation shows that mass
(arrows) is substantially smaller and almost uniformly hypodense.
Midline shift is now barely discernible.
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Discussion
Intracranial granulocytic sarcomas have been described in both infra- and
supratentorial locations. They may present as intraaxial masses but are more
frequently encountered in an extraaxial location. On MR imaging, granulocytic
sarcomas are typically iso- to slightly hypointense on T1- and isointense on
T2-weighted images relative to brain tissue
[3]. When gadolinium is
administered, uniform enhancement is usually noted
[4]. Tumors from other causes,
however, are typically hyperintense on T2-weighted imaging. Identification of
tumor involvement in bone marrow has also been reported on MR imaging, and
this finding may enable the radiologist to more confidently suggest the
diagnosis of a granulocytic sarcoma
[5]. Bone marrow involvement
was not apparent in our patient, however.
It is believed that intracranial granulocytic sarcomas develop by migration
of leukemic cells from the bone marrow via haversian canals, the periosteum,
and the dura to infiltrate the brain, where the pial—glial barrier has
been disrupted [6]. This
process would explain why most reported intracranial granulocytic sarcomas
occur adjacent to the inner calvarial table and present as extraaxial masses.
In our patient, contrast-enhanced MR imaging was performed at the beginning of
the patient's workup. On this scan, the tumor was slightly hypointense on T1-
and isointense on T2-weighted imaging, was strongly enhanced with gadolinium,
and contained several internal flow voids. The tumor was thus similar to
reported MR imaging characteristics of a granulocytic sarcoma, which therefore
became the primary diagnostic consideration. Histologic sampling established
this diagnosis.
On initial CT, intracranial granulocytic sarcomas are typically seen as
iso- or hyperdense masses [6].
On CT, granulocytic sarcomas may simulate meningiomas or may present as
cerebellopontine-angle masses such as acoustic neuromas
[3]. Uniform contrast
enhancement is usually present
[6]. Central hypodense areas
that are believed to represent tumor necrosis have been identified on or
mentioned in two reports of initial CT scans
[6,
7]. The initial CT
characteristics that have previously been reported are similar to the ones
seen in our patient on the initial unenhanced CT examination. However, on
short-term unenhanced CT follow-up, the tumor dramatically and entirely
changed its attenuation from hyper- to hypodense, which likely represented
complete tumor liquefaction and necrosis. The occurrence of these extensive
interval attenuation changes of intracranial granulocytic sarcomas after the
initiation of steroid therapy has not previously been reported. Complete
resolution of granulocytic sarcomas after the conclusion of radiation
treatment has been reported
[6].
Necrotic centers of granulocytic sarcomas have been described in previous
reports. Granulocytic sarcomas may have a tendency to form necrosis even
without treatment [6,
7]. The imaging changes that we
encountered may thus reflect a natural short-term evolution of the tumor, in
which case an entirely hypodense granulocytic sarcoma may be encountered on
initial CT.
Cases with attenuation changes from hyper- to hypodense are also mentioned
in the report by Pagani et al.
[8]. However, in that series
the eight patients with focal leukemic and lymphomatous intracranial masses
had undergone chemotherapy as well as radiation therapy before the attenuation
changes occurred. Our patient, in contradistinction, had been administered
only steroid treatment to reduce the peritumoral vasogenic edema.
To our knowledge, our report is the only documented description of a
granulocytic sarcoma shown to consist of an almost entirely hypodense lesions
on unenhanced CT. The radiologist should be aware that this finding may on
rare occasion be encountered in granulocytic sarcoma.
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Introduction
Case Report
