Keywords
osseous sarcoidosis - neurosurgery - histopathological diagnosis - skull sarcoid
Case Report
A 32-year-old Caucasian female was referred to neurosurgical outpatients for evaluation
of an asymptomatic left calvarial lesion. Past medical history was significant for
type 2 diabetes mellitus and asthma, treated with metformin and inhaled fluticasone,
respectively. On physical examination she was a morbidly obese lady (BMI 42.9 kg/m2). She had no focal or abnormal neurological findings on examination.
The left frontoparietal calvarial osteolytic lesion, 1.3 × 1.4 cm, was incidentally
detected on computerized tomography (CT) scan 2 years prior for evaluation of left
sided 7th cranial nerve palsy which spontaneously resolved ([Fig. 1]). There was no associated focal enhancement and the leading differential at the
time was of a simple benign hemangioma. Interval CT scan performed 18 months later
reported an increase in size of the lesion to 1.6 × 2.6 cm with new endosteal scalloping
laterally and medially with the appearance of erosion through the parenchymal diploic
cortex ([Fig. 2]). Once again, there was no focal or meningeal enhancement.
Fig. 1 Axial CT and contrast-enhanced MRI imaging of osseous lesion on diagnosis. CT, computerized
tomography; MRI, magnetic resonance imaging.
Fig. 2 Axial CT and contrast-enhanced MRI imaging of osseous lesion at 18-month follow-up.
CT, computerized tomography; MRI, magnetic resonance imaging.
Serial magnetic resonance imaging (MRI) of the brain demonstrated an enhancing, expansile
lesion in the left frontal bone, increasing in size from 17 × 7 to 34 × 13 mm over
2 years. There were no intracranial areas of abnormality or enhancement. Other investigations
revealed an unremarkable full blood count and liver function tests. Corrected calcium
was mildly low 2.24 mmol/L (range: 2.25–2.65 mmol/L) with normal creatinine and phosphate.
Serum angiotensin-converting enzyme (ACE) level was within normal limits. Chest X-ray
was unremarkable. Bone scan was requested but the patient declined.
The lesion was resected with no postoperative neurological changes. Histopathological
examination revealed large numbers of naked granulomas consistent with sarcoidosis
([Fig. 3]). Rheumatological consult was sought with the diagnosis of localized sarcoidosis
of the skull made. Given the absence of features of systemic sarcoidosis, the patient
did not receive systemic therapy and is for surveillance follow-up in Rheumatology
outpatients.
Fig. 3 Bone with fibrosis of marrow and “naked” nonnecrotising granulomas typical of sarcoidosis
(Haematoxylin and Eosin).
Discussion
Sarcoidosis is a systemic inflammatory disorder characterized by noncaseating granulomas.[1] It can involve multiple organs including the lungs, lymph nodes, skin, and eyes
with bone involvement being uncommon, affecting 3 to 13% of patients.[2]
[3] Bone involvement generally occurs as part of chronic multisystem, extrathoracic
disease, and has been associated with uveitis or lupus pernio.[4]
[5] Osseous sarcoid as an initial presentation is extremely rare and multiple bones
are usually involved.[5]
Further, osseous sarcoidosis affecting the skull is very rare, with the most frequent
site of involvement being small tubular bones particularly of the hands and feet.[4]
[6] The first case with sarcoidosis of the skull was described by Nielsen in 1934. A
classic series of patients with osseous sarcoidosis by Neville in 1977 described only
1 patient out of 29 with skull involvement.[4] A large series in Spain, conducted over 15 years with 425 patients, reported only
one case with osteolytic skull lesions.[7] The occurrence of solitary skull lesions is rare.
Radiographically, skull sarcoidosis most frequently appears as osteolytic lesions
without reactive or sclerotic changes, although permeative and destructive patterns
can occur.[5]
[8] The lesions are asymptomatic in up to 50% of cases.[9] The differential diagnosis for such lesions is broad and includes metastatic bone
disease, multiple myeloma, lymphoma, infection, Paget's disease, and osseous hemangiomas.
In the absence of prospective trials, optimal treatment of skull sarcoidosis is unknown
with the role of systemic corticosteroids being uncertain[10] and the natural course unpredictable.[11]
An additional interesting point was the clinical history of unilateral 7th nerve palsy
prior to the diagnosis of bony sarcoidosis. This raises the question of possible preceding
neurosarcoidosis. This is an uncommon manifestation of sarcoidosis, occurring in 5%
of patients.[12] Isolated neurosarcoidosis without other systemic signs is rare.[13] MRI brain performed for our patient at the time of symptoms did not demonstrate
any corresponding abnormality; however, it is reported that MRI abnormalities occur
in only 70% of cases[14]; no further ancillary investigations, such as cerebrospinal fluid (CSF) examination,
were performed. This reflects the literature as a definitive diagnosis is often not
achieved; histopathological diagnosis is difficult and the clinical presentations
are heterogeneous. A tentative diagnosis is often based on characteristic neurologic
features in a patient with a systemic diagnosis of sarcoidosis.[15]
This case reiterates several important issues. It highlights that skull sarcoidosis,
while exceptionally rare, should be considered in the differential diagnosis of osteolytic
skull lesions, even in the absence of other chronic multisystem manifestations of
sarcoidosis or multiple osseous lesions. It also reiterates the importance of biopsy,
with the characteristic histopathological finding of noncaseating granulomas, to secure
the diagnosis and direct management.
