Olfactory Groove Meningioma

Axial T2W MR image shows a lobulated extraaxial mass in the midline anterior cranial fossa. The mass is T2 isointense with a central area of higher T2 signal intensity. Mild brain edema of the inferior frontal lobes are noted. 

Sagittal post-contrast T1W MR image shows uniform enhancement of the mass.  It better demonstrates the location of the mass that is anterior to the tuberculum sellae.

Facts: Olfactory Groove Meningioma

• Usually asymptomatic until large. 
• When symptomatic, they can produce Foster Kennedy syndrome (anosmia, ipsilateral optic atrophy, contralateral papilledema), metal status change, urinary incontinence
• Histological variables follow WHO grading I to III (from low recurrence to high rates of recurrence with aggressive growth)
• Atypical meningioma, rhabdoid and malignant meningioma have greater risk of recurrence
• Brain invasion increases likelihood of recurrence but not indicator of malignant grade
• "Olfactory groove" is anterior to tuberculum sellae (distinction between tuberculum vs olfactory groove meningioma). Tuberculum sellae is bony elevation between chiasmatic sulcus and sella turcica. See tuberculum sellae meningioma here (external site)

MRI Findings

• T1 and T2 isointensity
• Most enhances with gadolinium
• Dural tail
• Signal voids in the lesion due to calcifications

Reference:

Cranial Base Center of Massachusetts General Hospital website 

Lipoma of Filum Terminale

Sagittal T1W image shows a T1 hyperintense mass at the filum terminale and a thin fatty strand extending from the tip of the conus medullaris to the coccyx.

Sagittal T2W image with fat suppression demonstrates signal loss of the mass, indicating presence of fat.

Facts:

• Abnormal retrogressive differentiation of pleuripotential cells found in distal caudal mass
• Mostly incidental, found in 5% of lumbar spine MRI but may be associated with tight filum terminale syndrome
• Fat is clearly separable from nerve roots and conus medullaris that terminates at above L2 level

Imaging

• Fat intensity mass (hyperintense T1, hyperintense T2, and progressive lower signal on greater T2 weighting)
• Can be intradural or extradural
• Intradural fatty filum is fusiform, tapering down toward where the filum pierces the dura
• Extradural fatty filum is often larger, more diffuse, elevating/distorting distal thecal sac

Reference:

Atlas SW. Magnetic resonance imaging of the brain and spine, 4th edition, 2009

Hemochromatosis

A&C: MRI out-of-phase imaging. B&D: MRI in-phase imaging
Signal decrease of the liver on B&D (in-phase images) when compared with A&C (out-of-phase images). Note innumerable Gandy-Gamna bodies in the spleen. 

Facts

• Hemochromatosis = iron overload
• Primary vs. secondary hemochromatosis
• Primary: autosomal recessive genetic disorder involving increased iron absorption. This is the most common genetic disease in white population
• Secondary: nongenetic causes of iron accumulation in organs such as cirrhosis, myelodysplastic syndrome, thalassemia
• Diagnosis is made with serum ferritin level and transferrin saturation index (but low sensitivity and specificity), genetic test and biopsy. Biopsy is reference standard
• Imaging such as non-contrast CT and MRI can be used to diagnose hemochromatosis but MRI is the best method

MRI Findings

• Iron accumulation in tissues cause local distortion of magnetic fields and spin relaxation, resulting in shortening T1, T2 and esp. T2* 
• Loss of signal intensity in affected organs proportional to iron deposition
• Dual-sequence (gradient in and out of phase) is typically used 
• Decreased signal intensity on in-phase images compared with out-of-phase images "opposite of hepatic steatosis"
• General MR protocols are not adequate to estimate hepatic iron concentration. Special sequences (i.e., GRE T2* with progressively longer echo times) are needed for this purpose
• Iron excess deposition may suggest etiology
• Reticuloendothelial system (i.e., liver and spleen): secondary hemochromatosis
• Parenchymal depositition pattern (i.e., liver only, possible pancreas): primary hemochromatosis or chronic anemia with insufficient erythropoiesis
• Mixed deposition pattern (atypical distribution): anemia+multiple blood transfusions

This patient has hemochromatosis secondary to cirrhosis. 

Reference:

Queiroz-Andrade M et al. MR imaging findings of iron overload. RadioGraphics 2009;29:1575-1589.