A 59 year-old woman presented with an approximate one-year history of worsening sensory disturbances and pain in the right side of her scalp and face.  Her past medical history was otherwise unremarkable.  Part of her initial work-up involved imaging of the head, which revealed multiple lytic lesions of varying sizes throughout the skull.    An unenhanced CT was done (Figure 1), and several circumscribed lytic lesions of varying sizes were seen throughout the calvarium.  There was no periosteal reaction or sclerosis surrounding the lesions.  There were no intracranial lesions. The patient was referred to a neurosurgeon for biopsy because no underlying primary tumor was found.

She continued to have similar symptoms post-operatively that prompted MR imaging of the brain (Figure 2). The images demonstrate several well-demarcated lesions that were T1 hypointense and T2 hyperintense when compared to bone marrow, with severe thinning of the adjacent cortex.  No intracranial lesions were present.  A T1 hyperintense right subdural collection was due to the recent surgery.

The differential diagnosis for multiple lytic lesions in the adult skull includes primarily metastatic disease and multiple myeloma.  Others include epidermoids, burr holes and in children, the histiocytoses.

What is your diagnosis?  Are there other rare causes of lytic osseous lesions in the skull?

The patient underwent a right frontal skull biopsy.  Pathology revealed non-caseating granulomatous inflammation, consistent with sarcoidosis.

Sarcoidosis is a multisystemic inflammatory disorder of unknown cause that is best known for pulmonary, lymph node, and cutaneous involvement.  Skeletal involvement is rare, occurring in an estimated 5% of patients.  Most common sites of involvement are the small bones of the extremities and the spine, where characteristic “lacy” lytic lesions are seen.  Primary involvement of the skull is extremely rare.  The first published report was by Nielsen in 1934, with less then 35 cases reported since.  When the skull is involved, the lesions are usually discovered incidentally.  When symptomatic, headaches or tenderness over the skull are the most common complaint.   Lesions in the skull can be solitary or multiple.  They are usually well demarcated, without periosteal reaction or perilesional sclerosis.  The lesions tend to appear less aggressive then metastases, with relative thinning of the inner and outer tables more common then frank destruction.  Also, extra-osseous soft tissue extension is less less likely with sarcoidosis.  For comparison, MR images of a calvarial metastasis from non-small cell lung carcinoma are pictured below (Figure 3).

Corticosteroids are the mainstay of treatment, although when isolated to the skull results can be disappointing.

In this case, the patient had no systemic symptoms of sarcoidosis.  Chest radiograph, and films of the pelvis, hands, and feet were normal.  The patient was treated ith steroids.

References:

1. Fernandez-Ruiz, M et al.  Sarcoidosis presenting as an osteolytic skull lesion: a case report and review of literature on skull sarcoidosis.  Clin Rheumatol, 2007; 26: 1745-1748
2. Landsberger D et al.  The skull in chronic sarcoidosis.  Postgrad Med J, 1998; 64: 875-877
3. Moore, SL et al.  Musculoskeletal sarcoidosis: spectrum of appearances at MR imaging.  RadioGraphics, 2003; 23:1389-1399