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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Pituitary Adenoma

Pituitary Adenoma

Tumors at the pituitary are classified by SIZE and by SECRETIONS. They are treated with medication, surgery, or active surveillance.

Size

A MICROadenoma is less than 1 cm and is often an incidental finding on an MRI of the brain done for other reasons, like workup of a headache. Unless it is secreting active hormone, a small adenoma is asymptomatic and will not cause visual disturbance or headache.

A MACROadenoma is larger than 1 cm and often presents with visual field cut due to compression of the optic chiasm. This produces tunnel vision, with a loss of peripheral vision called bitemporal hemianopsia.Pituitary macroadenoma. MRI T1 with contrast

Secretions

Pituitary tumors are also classified by secretions.

A “non-functioning” adenoma does not secrete active hormone. It may actually suppress the production of normal hormones, with TSH, LH, and FSH being most vulnerable. Paradoxically it can result in *mild* elevation of PRL to about 20-100. It is often discovered by visual field loss caused by compression of the optic chiasm causing bitemporal hemianopsia.

Functioning” pituitary adenomas secrete active hormone. These tumors may secrete any hormone, but PRL, GH, and ACTH are by far the most common.

A PRL secreting tumor mimics the postpartum state in females, with amenorrhea and galactorrhea.  In males it’s even worse: impotence and poor libido! A prolactinoma can be quite large on initial presentation, and the serum PRL may measure in the several hundreds. Fortunately, these are nicely responsive to dopaminergic drugs like bromocriptine and cabergoline, shrinking the tumor dramatically within a few weeks.

A GH secreting tumor causes acromegaly in adults and giantism in children. Acromegaly in adults can occur insidiously, barely noticed by the patient and close family. On questioning the patient may admit enlarged hands and feet such that rings and shoes have been resized. Other stigmata include an enlarged brow, protruding jaw, or enlargement of the cartilaginous nose. One patient noticed that he could floss easier as his teeth separated due to elongation of the jaw! Surgery is needed to remove this tumor.

An ACTH secreting adenoma causes Cushing’s disease, named for Harvey Cushing, the father of neurosurgery. ACTH production in the pituitary stimulates production of cortisol in the adrenal gland. This produces clinical hallmarks of Cushing’s: moon face, buffalo hump, abdominal obesity with striae, wasting of arms and legs, and easy bruising. This, too, is a surgical condition.

Treatment

Non-functioning MICROadenomas: No intervention needed, just periodic MRIs to check for growth, and periodic labs to check endocrine function.

Non-functioning MACROadenoma: Check endocrine labs, especially thyroid and sex hormones which can be diminished in the presence of a tumor. Check visual fields for bitemporal hemianopsia. Transphenoidal adenomectomy surgery can remarkably restore visual fields.

Prolactinoma: Pro-dopamine drugs like bromocriptine or cabergoline shrink the tumor dramatically and help with symptoms in males and females.

GH or ACTH secreting tumors usually need surgical resection to correct the harmful effects of these excess hormones.

Brown-Sequard Syndrome: Hemisection of the Cord

Brown-Sequard syndromeBrown-Sequard Syndrome

Injury to half the spinal cord, or “hemisection of the cord,” can occur with trauma, tumor, or disc herniation. But most often it is seen in textbooks and in med school exams! The injury produces a unique constellation of findings: loss of motor and fine touch on the same side as the injury, and loss of pain/temperature on the opposite side. This is the Brown-Sequard syndrome.

Here’s how it happens.

First to orient you to the cartoons. We all know what this is.

The Brain, actually!

The brain, actually!

And now the brain with the brainstem and spinal cord.

Brain, brainstem, spinal cord

Of all the tracts in the spinal cord, there are really only three you need to know to get started. There is one efferent pathway, the corticospinal tract that carries motor signals from the brain to the body. There are two afferent pathways that carry sensory information to the brain, the dorsal columns which carry proprioception and fine touch, and the spinothalamic tract which transmits pain and temperature.

Note the location of the “crossover” of these tracts. This crossover point is the key to understanding the clinical features of the Brown-Sequard syndrome. The corticospinal tract and the dorsal columns cross over in the medulla, at the “decussation of pyramids.”

Corticospinal tract

Dorsal columns

By contrast, the spinothalamic tract doesn’t cross to the opposite side until it exits from the cord.

Spinothalamic tract

So what if you have an injury to the left side of the cord. What will be the expected clinical findings? What neuro deficits will result?

Left hemisection of the cord

This is the Brown-Sequard syndrome. Loss of motor and fine touch ipsilateral to the lesion, and contralateral loss of pain and temperature.Ipsilateral loss of motor and fine touch

Subdural Hematoma: When to Cut

Subdural Hematoma: When to Cut

Subdural hematoma is a common neurosurgical problem. A subdural usually occurs in patients with significant brain atrophy, such as the elderly or alcoholic. Even minor trauma can injure the bridging veins between the brain and the dura. Bleeding into the subdural space can occur rapidly, causing death in a matter of hours, or gradually over a period of weeks. The surgical management depends on whether the hemorrhage is acute or chronic.

Acute Subdural Hematoma

An acute subdural may result from trauma or in a patient on antiplatelet or anticoagulant drugs. Symptoms often include headache, hemiparesis or alteration of consciousness like agitation, lethargy, or coma. If the acute subdural is small, it can be managed non-surgically. Antiplatelet drugs are stopped, and coagulation is corrected. Careful clinical observation is imperative. The subdural may expand as it becomes chronic, as the osmotic effect of the blood products draws free CSF into the subdural space. All this to say, if a small, acute subdural isn’t surgical today, it may be in two weeks!

Here a moderate sized, acute subdural is seen. You will notice a hyperdense (white) mass over the cortical surface of the brain (arrow), with effacement of the gyral pattern adjacent to the subdural, along with asymmetry of the lateral ventricles and midline shift.

Acute subdural hematoma

This patient was taken to surgery for a craniotomy. In the craniotomy, a large section of the skull was removed. This is called “turning a flap.” It allows the evacuation of the blood clot. At surgery, the clot was so tenacious it could be picked up with forceps. This, by the way, is the reason that an acute subdural cannot be drained with a bur hole. The blood is congealed. It cannot be drained with a bur hole any more than a cup of Jello can be eaten with a straw: it is solid. Air is introduced into the head at the time of surgery. It appears jet black on CT (arrow).

Acute subdural hematoma post op

Chronic Subdural Hematoma

On CT, a chronic subdural is hypodense (dark). It represents old blood in a liquid state. How old is old? It takes about two weeks for an acute subdural to liquefy, and the CT appearance will evolve from hyperdense to hypodense as the hemorrhage becomes chronic. Symptoms include headache on the same side as the subdural. Hemiparesis may be mild or well compensated as weakness occurs gradually. Many patients experience hemiparesis as gait imbalance, or veering to one side. As the patient worsens, frank lethargy or coma may ensue.

Here is a chronic, subacute subdural hematoma. You see a hypodensity over the cerebral convexity anteriorly (double arrow), with a hyperdense component posteriorly (arrow). There is effacement of the gyral pattern, ventricular asymmetry and midline shift.

Subacute chronic subdural hematomaChronic subacute subdural hematoma with labels

This patient was taken to the operating room for bur-hole evacuation of the subdural. The liquefied blood was removed with a simple bur hole. Going back to the Jello analogy: If you leave Jello at room temperature, it turns to liquid; in this case you CAN drink it with a straw. Or drain a chronic subdural with a bur hole!

Here you can see postoperative air in the head (jet black, see arrow), with a mix of residual chronic and subacute blood, with improved mass effect. A drain is present (double arrow).

Chronic subdural hematoma post opChronic subdural hematoma post op with labels

To summarize, an acute subdural is a life threatening emergency, often requiring craniotomy within hours. The chronic subdural can be life threatening as well, but over a period of weeks, often treated with simple bur hole drainage.

Books and other resources

Aside

Books and other resources

The learning curve is steepest at the beginning, and in neurosurgery you’ll never stop learning. I’ve received the greatest help from these:

Andrew H. Kaye, Essential Neurosurgery, 2005.Readable, simple overview of all the basics This is where you start. A very readable introduction to the brain and spine disorders and treatment, it is written on the level of the medical student or intern rotating on the neurosurgery service. 

Mark S. Greenberg, Handbook of Neurosurgery, 2010. A thousand-page “handbook” can be pretty intimidating, but it actually fits in your lab coat pocket.

It contains all the common neurosurgical problems you’ll have to manage, with plenty of cookbook formulas so you’ll know just what to order in patient care.

1000 pages of Awesome

Setti Rengachary, Principles of Neurosurgery, 2004. Far more emphasis on brain than spine, this one volume introduction is chock full of charts, diagrams and drawings to give you the big picture of neurosurgical problems. Concise, readable, relevant, this one is a real pleasure to read.One-volume textbook loaded with charts, diagrams

Daniel H. Kim, Surgical Anatomy and Techniques to the Spine, 2005. The pictures and diagrams are worth the price of the book, and in fact are included on a CD for handy electronic reference. I’ve even copied a page or two for patient education: “This is what will be done in your surgery.”Surgery in step-by-step drawings

And finally, just to keep you honest:

You don’t have to buy Duane E. Haines, Neuroanatomy An Atlas of Structures, Sections, and Systems, 2004. You lost me at hello. Sorry. It’s like  Netter’s Atlas on steroids: just too many named structures for a beginner. And that’s what this list is about.