Cranial fossae: Anterior, middle and posterior

How would you describe the location of this mass?Describe the location

a. Cerebellar

b. Infratentorial

c. Posterior fossa

d. Suboccipital

Answer: All of the above.

All these terms refer to the same space. The cerebellum resides in the posterior cranial fossa, in a location that is infratentorial or suboccipital.

Please note the “occipital” and “suboccipital” are NOT synonymous. (“Occipital” refers to the occipital lobe which is a part of the cerebrum and is supratentorial.)

The term “fossa” refers to a “scooped out” space, like the palm of your cupped hand. There are three fossa of the skull base: anterior, middle and posterior.

Cranial fossae

The anterior fossa (green) is where the frontal lobe is located.

The middle fossa (purple) is where the temporal lobe is located.

The posterior fossa (orange) is where the cerebellum is located.

The mass presented above is a tumor of the posterior fossa, that is, in an infratentorial location. It abuts the cerebellum. Surgical resection may be achieved through a suboccipital craniectomy.

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Glioblastoma: Growth rate

Glioblastoma: How fast do they grow?

A 57 year old female presented with new onset seizure. An MRI was obtained showing a lesion in the right frontal/parietal region. You can see there is some mass effect, slight effacement of the ventricle, and a whiff of enhancement. Needle biopsy returned astrocytoma, WHO Grade 3.Astrocytoma WHO Grade 3

Surgical resection was recommended, but the patient chose instead to pursue external beam radiation and oral chemotherapy in the form of temozolomide.

Unfortunately, she now presents three months later with confusion, agitation, and left arm weakness. An MRI is again obtained. The tumor shows marked growth and different signal characteristics. You see that the mass is inhomogeneously enhancing, with marked mass effect, surrounding edema, ventricular effacement, and minimal midline shift.

Glioblastoma, WHO Grade 4

At this time the patient requests craniotomy for surgical debulking. The final pathologic diagnosis is Glioblastoma, WHO Grade 4.

This shows how rapidly a glioma can grow and transform to a higher grade, in this case just three months.

Lumbar MRI: systematic reading

Lumbar MRI: a systematic reading

Alignment – Vertebrae – Conus – Cauda – Disc – Foramen

The most common pitfall in reading a lumbar MRI is focusing on the most obvious abnormality. It’s easy to do: your eye naturally goes to the vertebral slip, or the huge herniated disc. That’s natural, but in every case also be sure to do a systematic reading of the entire study. You’ll save yourself the pain and liability of missing a significant “incidental” finding.

So how to read the lumbar MRI systematically? Alignment – Vertebrae – Conus – Cauda – Disc – Foramen

Alignment: look at the normal lordosis, and also look at the posterior marginal line for a slip of vertebrae out of place.

Vertebrae: what is the quality of the marrow signal? Increased or decreased signal may be associated with metastatic tumor or discitis/osteomyelitis, or the modic changes of severe disc degeneration at the vertebral end plates.Lumbar MRI T2 Sagittal

Conus: evaluate the position and caliber of the conus. A thickened conus may herald an intramedullary tumor such as ependymoma. The conus usually terminates about L1-2.

Cauda equina: Is there stenosis of the central spinal canal, or clear cut compression of the cauda equina? The CSF signal is normally generous at all levels of the spine. Loss of CSF signal is the hallmark of spinal stenosis. On axial images the canal itself may have a triangular, trefoil, appearance.

“In  this lumbar MRI T2 weighted sagittal, there is a normal lordosis, with a 7 mm anterolisthesis of L4 on L5, with abnormal high signal in the L4 and L5 vertebral bodies. The conus ends at L1-2 and appears normal in caliber and signal. There is moderate stenosis at L4-5. Except for L4-5, the discs are normal in height and signal. The intervertebral foramen are not evaluated on this midline sagittal image.”

Disc: a herniated disc is “protruded” if the bulge is wider than it is deep, or “extruded” if deeper than it is wide. Evaluate all the discs, not just the most obvious one.

Foramen: Look at the lateral slices on the T1 sagittal. Do you see the intervertebral (neural) foramen? It should be patent. You will see a white “fat pad” at each opening, with the dark nerve root coursing through. Loss of the white fat signal suggests impingement of the nerve in the foramen.

Lumbar MRI T1 sagittalLumbar MRI T1 axial” Left lateral sagittal and axial MRI T1 weighted images show obliteration of the fat signal in the L4-5 intervertebral foramen, confirmed on axial imaging through the L4-5 disc where a left lateral extrusion of disc is identified.”