Sarcoidosis

Look For First

Bilateral parotid enlargement with multiple hypoechoic nodules on ultrasound or multiple small hypodense foci on CT (representing granulomas and enlarged intraparotid nodes)
Ga-67 nuclear medicine panda sign: bilateral symmetric parotid and lacrimal gland uptake alongside physiologic nasopharyngeal activity
Non-cavitating T1-hypointense, T2-hyperintense nodules on MRI that may show variable enhancement
Coarse heterogeneous echotexture with enlarged intra- and periglandular nodes

Key Image Findings

Ultrasound demonstrates multiple solid hypoechoic areas or diffuse low echogenicity within enlarged or normal-sized parotid glands, often with calcific foci and coarse heterogeneous texture with enlarged intraparotid and periglandular nodes.
CT shows enlarged, inhomogeneous glands with multiple small punctate hypodense foci after contrast administration, sometimes described as 'foamy' appearance, with heterogeneous enhancement reflecting both granulomas and varying glandular fatty infiltration.
MRI nodular pattern exhibits non-cavitating lesions that are T1-hypointense and T2-hyperintense with variable enhancement ranging from ill-marginated enhancing lesions to nodules with minimal enhancement.
MRI diffuse pattern shows symmetric parotid enlargement with increased T2 signal and intense, usually homogeneous enhancement throughout the gland.
Ga-67 nuclear medicine imaging demonstrates the panda sign in 79% of sarcoid patients—bilateral parotid and lacrimal uptake alongside physiologic nasopharyngeal activity; specificity increases when panda is combined with lambda sign or symmetric hilar adenopathy.
FDG PET shows parotid uptake in a similar distribution to the panda sign, though brain activity may partially obscure the pattern, and this uptake is nonspecific.
Disease typically presents without a discrete dominant mass or periparotid inflammatory change, distinguishing it from neoplastic processes.
Accessory parotid tissue can be involved with identical imaging signal characteristics as main parotid involvement.

Differential Diagnosis

Sjögren syndrome: characterized by sialectasis, cysts, salt-and-pepper or honeycomb gland pattern with fat deposition—findings not expected in sarcoid; 5–6% of Sjögren patients develop MALT lymphoma.
Lymphoma: presents with multiple intraparotid nodules and bilateral cervical adenopathy, mimicking the multinodular pattern of sarcoid but typically lacks the characteristic panda sign on Ga-67 imaging.
HIV lymphoepithelial lesions: show polycystic change within an otherwise unremarkable gland, distinguishing them from sarcoid's nodular or diffuse enhancement pattern.
IgG4-related disease: preferentially involves submandibular glands rather than parotids and typically presents bilaterally with different morphologic features.
Other granulomatous diseases: tuberculosis, granulomatosis with polyangiitis, and histoplasmosis may show identical imaging appearance and require clinical and microbiologic correlation for diagnosis.
Parotid malignancy with perineural spread causing facial palsy: must be excluded in patients presenting with unilateral parotid mass and cranial nerve involvement.

Discussion

Bilateral parotid involvement is the classic teaching pattern, but unilateral disease occurs in up to 86% of population-based cohorts and does not exclude sarcoidosis; painless enlargement is typical.

The diagnosis of parotid sarcoidosis cannot be made by granulomas on fine-needle aspiration alone—compatible clinical and imaging findings plus exclusion of other granulomatous causes (including sarcoid-like reactions from metastatic malignancy) are required.

The combined Ga-67 panda plus lambda signs or panda plus symmetric hilar adenopathy on chest imaging provide diagnostic specificity superior to panda sign alone, potentially avoiding diagnostic parotidectomy.

Heerfordt syndrome (parotid enlargement with anterior uveitis, facial palsy, and fever) is rare, occurring in only 0.3% of sarcoid cases in complete form and 1.3% in incomplete form.

Six of seven patients in a population-based cohort had intrathoracic sarcoidosis; therefore, chest imaging is essential to support the diagnosis and assess systemic disease burden.

Supportive imaging findings include lacrimal gland enlargement (present in ~10% of sarcoid patients) and posterior triangle cervical lymphadenopathy (palpable in ~one-third); labial gland biopsy shows 19% yield but effectively separates sarcoid from Sjögren syndrome.

Reporting Pearls

Describe parotid sarcoidosis as "bilateral symmetric parotid enlargement with multiple hypoechoic nodules (or small hypodense foci on CT) representing granulomas and enlarged intraparotid nodes; no discrete dominant mass or periparotid inflammatory stranding is present," and note that supporting findings such as lacrimal gland enlargement and cervical lymphadenopathy strengthen the diagnosis; always recommend correlation with chest imaging for intrathoracic sarcoidosis.

Pitfalls

Unilateral parotid involvement may be mistaken for primary parotid neoplasm or lymphoma, but imaging features (nodular pattern, lack of dominant mass, supported by panda sign on Ga-67) and clinical context help differentiate; at least 86% of population-based cases present unilaterally.
The panda sign on Ga-67 imaging is not specific for sarcoidosis—it occurs in HIV, lymphoma, and Sjögren syndrome; specificity improves when combined with lambda sign or hilar adenopathy on chest imaging.
Solitary enhancing masses or intraparotid nodules representing granulomas can mimic primary parotid malignancy or metastatic lymph nodes, particularly if facial palsy is present; careful evaluation of enhancement pattern and lack of perineural spread are key discriminators.
FDG PET uptake in the parotid glands is nonspecific and can mimic lymphoma; nuclear medicine panda sign combined with clinical-radiologic correlation provides better diagnostic specificity than PET alone.

Sarcoidosis

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