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