The Vidian Canal

The vidian canal is a landmark in the skull base that transmits the vidian nerve and vidian artery.

The vidian nerve is formed from the greater/large superficial petrosal nerve of CN V (sympathetics) and the deep petrosal branch (parasympathetics).   (There's also an ascending sphenoid branch from the otic ganglion).

The vidian canal transmits the nerve from the foramen lacerum to its exit at the pterygopalatine fossa.

Tracing the vidian canal superior to inferior.  It originates at the pterygopalatine fossa (arrow) and proceeds through the skull base (circle).  The branch point in the third image represents the take-off of the GSPN into the middle ear through the "hiatus" of the greater "superficial" petrosal nerve (longer left branch).  The smaller branch represents the deep petrosal nerve joining the GSPN with its post synaptic carotid nerve fibers.

Three variations of the vidian canal have been described with varying degrees of bony coverage (below).

Incidentally, The term vidian is derived from an anatomist, "Vidus."

Renal osteodystrophy and diffuse skull thickening

Although not difficult to detect, the challenge in diffuse skull thickening is suggesting a correct etiology from a wide range of possibilities.

The range of possible etiologies includes:
- Normal variant (most common etiology), Acromegaly, Microcephaly
- Chronic shunting
- Chronic Dilantin/Phenytoin use
- Diffuse osteoblastic metastases
- Paget disease
- Extramedullary hematopoeisis (esp. B-thalassemia)
- Osteopetrosis
- Hyperparathyroidism (either primary or secondary)

In the example above, the patient had a known diagnosis of renal osteodystrophy, and the thickened calvaria were attributed to that cause.

Findings in diffuse skull thickening from renal osteodystrophy are described as "loss of distinction between the inner and outer table" and a "granular deossification of the skull" ("salt and pepper skull") due to small lytic foci interspersed with normal bone. (below)

Brown tumors can occasionally occur in this setting (below).  Cranial neuropathy from narrowing of foramina has also been described.

"Salt and Pepper" appearance of the skull with a focus of brown tumor (arrow).

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1. Baird IM,  Lees F, "Renal Osteodystrophy in Adults" AMA Arch Intern Med. 1956;98(1):16-22. 

2. Burgener F, et al. "Differential Diagnosis in Conventional Radiology" 3rd ed (2008), pp. 218-219