Intradural spinal involvement in leukemia

Clinically significant intradural spinal involvement in leukemia, in contrast to intracranial, especially meningeal, involvement is rather uncommon ¹¹. As with intracranial CNS involvement, involvement of the spinal cord or its coverings as the first manifestation of systemic leukemia is rare. More commonly, however, the CNS is involved in patients with known acute leukemia or in patients believed to be in remission following antileukemic therapy ¹.

CNS involvement may be either meningeal on parenchymal, however the overwhelming majority of cases are meningeal (typical leptomeningeal) ¹. Although usually extradural in location, granulocytic sarcoma may rarely be intramedullary. Transverse myelopathy secondary to leukemia has also been reported ⁸.

The precise mechanism of leukemic infiltration into the CNS is unknown, but may involve hematogenous spread as well as direct spread from adjacent involved bone marrow ¹.

Meningeal disease (leukemic meningitis)

Infiltration of the meninges by leukemic cells may affect the dura or leptomeninges, although the latter is far more common. Infiltration may be diffuse or focal ¹. Among patients with meningeal leukemia, only 5-10% develop clinically detectable disease of the spinal cord ³.

Acute leukemia, in particular acute lymphocytic leukemia (ALL), has the highest propensity to invade the meninges. Chronic leukemia (chronic lymphocytic and myelogenous), rarely causes leukemic meningitis ².

The presence of leukemic meningitis is a predictor of poor outcome ².

Radiographic features

MRI

• T1 and T2: thickening or clumping of the nerve roots/cauda equina
• T1 C+ (Gd)
  • “sugar coating” of the spinal cord and nerve roots
  • enhancing tumor nodules on the spinal cord, nerve roots or cauda equina

MRI may be normal in the presence of meningeal disease; the absence of MRI findings does not therefore exclude the diagnosis, which is ultimately made by CSF analysis.

Leukemic infiltration of the spinal cord

Direct symptomatic invasion of the spinal cord is exceedingly rare but has been described in case reports ^{3, 4, 7}

Radiographic features

Reported MRI characteristics include ⁷:

• T2: hyperintense signal
• enlargement of the spinal cord

Granulocytic sarcoma

Granulocytic sarcoma (chloroma, myeloblastoma) is an extramedullary mass composed of immature granulocytic cells. It occurs primarily in patients with acute myelogenous leukemia (AML) but also may arise in patients with other myeloproliferative disorders ⁷. The tumor is reported in 0.7-9.0% of patients with acute or chronic myelogenous leukemia ⁵.

The most common sites of occurrence are the orbits, skin, bones, and sinuses. Within the spine, granulocytic sarcoma usually occurs as an epidural mass; however, a few cases of intramedullary involvement have been reported ⁵.

Radiographic features

CT

• isodense to hyperdense
• demonstrates contrast enhancement

MRI

• T1: isointense
• T2: hyperintense
• T1 C+ (Gd): variable enhancement
• cysts or necrosis are not typically observed ¹