Salt and Pepper Skull: Hyperparathyroidism on X-ray and CT

Answer:

Salt and pepper skull is a granular calvarium: innumerable tiny lucent foci of trabecular resorption mixed with small sclerotic foci, with blurring of the inner and outer tables. It is caused by osteitis fibrosa cystica, the florid bone disease of excess parathyroid hormone, in primary, secondary or tertiary hyperparathyroidism. If the parathyroid hormone level is normal or low, the pattern is something else.

Why is it called so?

The calvarium looks as though salt and pepper have been scattered across it: the white grains are the sclerotic foci, the black grains the lytic ones. Pepper pot skull names the same appearance.

Pathophysiology

Parathyroid hormone drives osteoclastic resorption, and it acts first on trabecular bone, which has the highest surface to volume ratio. In the calvaria the cancellous bone takes on a granular texture as lytic foci are interspersed in bone of normal density, and this may lead to loss of distinction between the inner and outer tables. The change is diffuse and symmetrical, because the stimulus is hormonal rather than focal.

Alternative names: Pepper pot skull, granular skull

Other associated named signs: Subperiosteal resorption, brown tumour, rugger jersey spine, acro-osteolysis

A late sign of a disease that is now caught earlier

Osteitis fibrosa cystica is no longer commonly seen in primary hyperparathyroidism in the Western world, because calcium is measured on routine panels and the disease is found biochemically years before the skeleton is remodelled. Two consequences follow for the radiologist. First, a salt and pepper skull today is far more often a marker of secondary hyperparathyroidism in chronic kidney disease, where bone resorption is the imaging hallmark of the systemic manifestations of kidney failure. Second, in parts of the world where hypercalcaemia is not screened for, florid skeletal disease is still the presentation: in the Indian primary hyperparathyroidism registry, 122 of 229 operated patients had skeletal involvement and only 45 were asymptomatic.

The mottled calvarium: what else it could be

The question is not whether the skull is mottled but whether the mottling is diffuse and granular or made of discrete lesions. Hyperparathyroidism and renal osteodystrophy involve the calvaria diffusely, whereas multifocal calvarial lytic disease is mainly haematologic or secondary malignancy. Parathyroid hormone settles it in one blood test.

Which hyperparathyroidism is it?

The skull cannot tell you which type produced it. The biochemistry can.

What to do when you see it

• Report the calvarium as diffusely granular, name hyperparathyroid bone disease, and ask for calcium, phosphate, parathyroid hormone, alkaline phosphatase and renal function. A suppressed parathyroid hormone redirects the whole work-up.
• Look at the hand and the spine on whatever imaging exists. Subperiosteal resorption of the radial side of the middle phalanges and rugger jersey spine confirm the diagnosis more convincingly than the skull does.
• Look for a brown tumour, which mimics a metastasis or a primary bone tumour and gets biopsied on that basis.
• Do not request a skull radiograph to diagnose or follow hyperparathyroid bone disease. The Fifth International Workshop directs skeletal assessment in primary hyperparathyroidism to three-site DXA (lumbar spine, hip, distal one third radius) plus vertebral fracture imaging, and KDIGO suggests bone mineral density testing in chronic kidney disease only where the result will change treatment.

Frequently asked questions

Is salt and pepper skull the same as pepper pot skull?

They describe the same granular calvarium and are used interchangeably. One caution: pepper pot skull has also been applied to multiple lytic lesions from other causes. In one report a 17 year old with lytic lesions of the skull, ribs and vertebrae, calcium of 14 mg per dL and a parathyroid hormone of 6.2 pg per mL had pre-B acute lymphoblastic leukaemia. The low parathyroid hormone was the clue.

Which hyperparathyroidism most often causes it today?

Secondary hyperparathyroidism of chronic kidney disease. Primary hyperparathyroidism is usually detected on a routine calcium level long before the calvarium remodels, so the florid skeletal picture is now uncommon where biochemical screening is routine.

Can you see salt and pepper skull on CT?

Yes, and better than on a radiograph. On bone windows the diploe shows the same granularity with loss of distinction between the inner and outer tables, and CT also shows the vascular and soft tissue calcification of renal osteodystrophy. It is nearly always an incidental finding.

Does the skull recover after parathyroidectomy?

Largely, yes. Successful parathyroidectomy is the definitive treatment for primary hyperparathyroidism and may promote regression of most skeletal defects, although remodelling of the calvarium is slow and some granularity can persist on imaging.

References

1. Khodarahmi I, Alizai H, Chalian M, et al. Imaging Spectrum of Calvarial Abnormalities. RadioGraphics. 2021;41(4):1144-1163.
2. Rajiah PS, Suman G, Vijay K, et al. Multisystem Imaging Manifestations of Kidney Failure. RadioGraphics. 2024;44(8):e230124.
3. Minisola S, Gianotti L, Bhadada S, Silverberg SJ. Classical complications of primary hyperparathyroidism. Best Pract Res Clin Endocrinol Metab. 2018;32(6):791-803.
4. Roumpou A, Palermo A, Tournis S, et al. Bone in Parathyroid Diseases Revisited: Evidence From Epidemiological, Surgical and New Drug Outcomes. Endocr Rev. 2025;46(4):576-620.
5. Bilezikian JP, Khan AA, Silverberg SJ, et al. Evaluation and Management of Primary Hyperparathyroidism: Summary Statement and Guidelines from the Fifth International Workshop. J Bone Miner Res. 2022;37(11):2293-2314.
6. Ketteler M, Block GA, Evenepoel P, et al. Executive summary of the 2017 KDIGO Chronic Kidney Disease-Mineral and Bone Disorder (CKD-MBD) Guideline Update. Kidney Int. 2017;92(1):26-36.
7. Mukherjee S, Arya AK, Bhadada SK, et al. Characterization of primary hyperparathyroidism based on target organ involvement: An analysis from the Indian PHPT registry. Clin Endocrinol (Oxf). 2023;99(2):158-164.
8. Jain A, Sharma P. Pepper-pot Skull in a Young Male Patient. Balkan Med J. 2020;37(6):355-356.