Immunoglobulin G4-Related Disease Involving the Pterygopalatine Fossa, Mimicking Invasive Aspergillosis: A Case Report and Literature Review.

We report a case of Immunoglobulin G4 (IgG4) related disease involving the pterygoplataine fossa. A 83-year-old male presented with left ocular pain and visual disturbance. CT showed an isodense soft tissue lesion in the left pterygopalatine fossa with bony sclerotic changes and erosion. MRI revealed an infiltrative soft tissue mass in the left pterygopalatine fossa as a T2 slightly low signal intensity and heterogeneous enhancement. The patient underwent left ethmoidectomy, and biopsy of the mass was conducted. The histopathological diagnosis was IgG4-related disease. In this case, it was difficult to differentiate invasive aspergillosis, which is common in immunocompromised patients, considering the patient's clinical history of diabetes mellitus. This report describes the imaging findings of IgG4-related disease mimicking invasive sinusitis such as invasive aspergillosis. Copyrights

INTRODUCTION

Immunoglobulin G4 (IgG4)-related disease is an autoimmune condition in which IgG4 plasma cells infiltrate into tissues as a result of increased serum IgG4 levels. The predominantly involved organs are the pancreas, salivary gland, and biliary tract (12). In the head and neck region, the salivary, lacrimal, and pituitary gland are frequently affected. It is very rare for IgG4-related disease to invade the nasal cavity or paranasal sinus. This case study aims to describe the imaging features of IgG4-related disease primarily involving the pterygopalatine fossa.

CASE REPORT

An 83-year-old male came to our clinic with left ocular pain and visual disturbance for a month. The patient had suffered from Type II diabetes mellitus and hypertension. He had no fever. White blood cell and eosinophil counts were in normal range. The neurological examination revealed mild limitation in the left lateral gaze. Nasal endoscopy showed polypoid mass-like lesion at the left middle meatus without mucopus. Based on clinical history of diaetes mellitus, sino-orbital infection such as invasive aspergillosis was suspected rather than inflammatory or tumorous condition.

On facial CT, isodense soft tissue mass was observed in the left pterygopalatine fossa with sclerotic change and erosion of the adjacent bone. There was accompanying soft tissue infiltration along the left optic nerve and extraocular muscles, suggesting orbital infiltrations. Mucoperiosteal thickening of the left maxillary, ethmoid, and sphenoid sinuses were also observed (Fig. 1A, B). We first suspected invasive sinusitis such as invasive aspergillosis, involving pterygopalatine fossa and other differential diagnosis are inflammatory pseudotumor (IPT) and lymphoma. MRI was performed to evaluate the characteristics and extent of this lesion. The mass-like lesion of the left pterygopalatine fossa presented heterogenous low signal intensity on T2-weighted images (T2WI) (Fig. 1C) and heterogeneous enhancement on contrast enhanced T1-weighted images (T1WI). It showed infiltrating nature and extended to the left cavernous sinus, left orbital muscles, and left masticator space (Fig. 1D). A diffuse enhancement along the left optic nerve and thickening of extraocular muscles (medial, inferior and lateral rectus muscles) were accompanied. There was no evidence of involvement in lacrimal gland and salivary gland.

Fig. 1

Imaging findings in an 83-year-old male with IgG4-related disease involving pterygoplatine fossa.

A, B. Axial images show an isointense soft tissue lesion in the left pterygopalatine fossa with sclerotic change and erosion of the adjacent bone (arrow, left image). Infiltration into the left orbital apex (arrow, right image) was accompanied (A). An isodense soft tissue lesion in the left pterygopalatine fossa infiltrates through the inferior orbital fissure (black arrows) into the orbital apex and extends to the maxillary sinus with bony erosion (white arrow) on sagittal image (B).

C, D. MRI. T2-weighted axial image (C) shows focal low signal intensity area (arrow) within mixed iso- to hypointense mass-like lesion occupying the left pterygopalatine fossa. Contrast enhanced T1-weighted images (D) reveal enhancement at the left pterygopalatine fossa infiltrating into the left cavernous sinus, left orbital muscles (black arrows), and left masticator space through the pterygomaxillary fissure (dashed arrow). IgG4 = immunoglobulin G4

E. Photomicrograph images of a sinonasal mass. Hematoxylin-eosin staining (× 400) shows dense lymphoplasmacytic infiltration with fibrosis (left). Immunostaining for IgG4 (× 400) reveals that the majority of plasma cells appear positive for IgG4 (right). Pathologic diagnosis was IgG4-related disease.

IgG4 = immunoglobulin G4

For diagnosis, we performed endoscopic sinus surgery. Left ethmoidectomy and biopsies of the sinonasal mass at nasal cavity were conducted. During the surgery, we noted an irregularly shaped pale brown-colored mass filling the left posterior ethmoid sinus. This mass was eroding the medial wall of the orbit. The part of the mass was removed. On hematoxylineosin staining, the sinonasal mass showed dense lymphoplasmacytic infiltration with fibrosis. Immunostaining for IgG4 showed the majority of plasma cells positive for IgG4 (Fig. 1E). Serum IgG4 concentration was checked after the surgery, showing upper limit of a normal range (85.7 mg/dL, reference range 3.9–86.4). The findings above met the 2019 American College of Radiology/European League Against Rheumatism classification criteria for IgG4-related disease (1). After surgery, the patient was treated with prednisolone.

DISCUSSION

IgG4-related disease is an autoimmune condition in which IgG4 plasma cells infiltrate into tissues with increased serum IgG4 levels, causing tissue fibrosis and resulting dysfunction of the organ. This disease entity recently has been noticed and reported (23). Clinical symptoms vary depending on the involved organ. Symptoms presented when sinonasal space or orbit involved with ocular pain, visual disturbance, headache, and chronic rhinitis, as noted in our case.

There are two different terminology “IPT” and “IgG4-related disease” commonly used in clinical field, sharing the pathologic feature of fibrosis and infiltration of lymphocytes and plasma cells. Although the relationship between IPT and IgG4-related disease has no definitely been established, recently IgG4-related disease is thought to form part of the spectrum of IPT according to the IgG4 level (4).

There are some differentials that should be considered when there is a lesion with T2 low signal intensity in the pterygopalatine fossa, such as lymphoma, invasive aspergillosis, Wegener's granulomatosis, and solitary fibrous tumor. Lymphoma shows soft tissue lesion with homogeneity and tends to remodel bone rather than lytic destruction which is different from our case (56). Considering the clinical presentation of immune compromised state with DM, invasive aspergillosis was on the top of clinicians' differential diagnosis. But, laboratory findings favored non-infectious disease.

IgG4-related disease is known to show intermediate attenuation on CT and relatively low signal intensity on T1 and T2 weighted MR images (2). But usually, imaging findings of IgG4-disease seem quite non-specific and it is difficult to differentiate from other diseases by imaging. However, this case may reveal images of IgG4 related disease, slightly different from the typical imaging findings of invasive aspergillosis, which may facilitate in differentiating. On MRI, this case showed as T2 iso to hypointense soft tissue mass. Conversely, the typical MR findings of invasive aspergillosis are extremely low signal intensity in T2WI images with bright homogenous enhancement in post-contrast T1WI (789). Additionally, in this case, orbital involvement was overt and appeared extensively, but the presented clinical symptom was quite mild and normal laboratory findings compared with the extent involved. This may be another differential point from invasive aspergillosis involving orbit which may accompany more aggressive clinical symptom such as sudden vision loss.

In conclusion, it is notable that when T2 slightly low signal intensity mass in pterygopalatine fossa shows infiltrating enhancement feature, radiologists should also be alert to the possibility that IgG4-related disease can mimic invasive aspergillosis.