2026 年 13 巻 p. 307-310
Inflammatory pseudotumor involving the cranial nerves is extremely rare, and delayed diagnosis may cause irreversible neurological deficits. To our knowledge, this represents the third reported case of an inflammatory pseudotumor involving the cavernous sinus with extension along the oculomotor nerve. A 56-year-old woman presented with a visual field defect in her left eye, and her condition was initially managed conservatively because of her mild clinical presentation. Initial magnetic resonance imaging revealed a homogeneously enhanced dumbbell-shaped mass lesion extending from the left cavernous sinus through the superior orbital fissure into the intraconal orbital space. At 3-year follow-up, the patient's condition worsened during routine outpatient visits, with left visual acuity decreasing to light perception. Surgical biopsy revealed a fibrous mass involving the cisternal portion of left oculomotor nerve and extending into the cavernous sinus. Histopathological examination and laboratory findings confirmed the diagnosis of an immunoglobulin G4-related inflammatory pseudotumor. Oral corticosteroid therapy caused marked radiological regression of the lesion; however, visual impairment was not alleviated. This case highlights that delayed histopathological confirmation may produce irreversible neurological deficits despite a favorable radiological response to corticosteroid therapy.
Inflammatory pseudotumor is a non-neoplastic lesion characterized by fibroblastic proliferation and infiltration of mixed inflammatory cells. It most commonly involves the lung, orbit, and gastrointestinal tract, and often mimics neoplastic processes on clinical and radiological evaluation. Rare cases of intracranial involvement have been reported;1,3) however, cranial nerve involvement remains extremely rare. To date, only 2 cases of inflammatory pseudotumor involving the cavernous sinus with extension along the oculomotor nerve have been reported.4,5) We herein report a rare case of an inflammatory pseudotumor involving the oculomotor nerve associated with immunoglobulin (Ig) G4-related disease, extending from the cavernous sinus into the orbit and causing progressive visual impairment due to optic nerve compression. The lesion was diagnosed by surgical biopsy and indicated a marked radiological response to corticosteroid therapy. This case highlights the importance of early biopsy-based diagnosis and recognition of IgG4-related disease in patients with unexplained oculomotor nerve lesions. We report this case to emphasize the diagnostic challenges and clinical features of IgG4-related inflammatory pseudotumor involving the cavernous sinus with extension along the oculomotor nerve.
A 56-year-old woman presented with left visual field defect 3 years before admission. Initial magnetic resonance imaging (MRI) revealed a homogeneously enhanced dumbbell-shaped mass lesion extending from the left cavernous sinus through the superior orbital fissure into the intraconal orbital space (Figure 1A). At the initial presentation, the lesion was considered more likely to represent a benign neoplasm such as schwannoma or meningioma on the basis of its imaging characteristics, although visual field impairment was present at the time of presentation. Given the lesion's deep location and the potential risk of neurological morbidity, a conservative approach with careful observation was selected. Serial MRI examinations were performed every 6 months, and no significant changes in the lesion were observed during the follow-up period. Three years later, at a routine outpatient follow-up, the patient's condition abruptly deteriorated, with left visual acuity decreasing to light perception only. Follow-up MRI showed interval enlargement of the lesion (Figure 1B and C). The lesion compressed the left optic nerve from the inferomedial side and followed the anatomical course of the inferior division of the oculomotor nerve. No preoperative oculomotor nerve dysfunction was observed; specifically, the patient did not exhibit ptosis, extraocular movement disturbance, or pupillary abnormalities. The serum IgG4 level was elevated to 269 mg/dL. It should be noted that serum IgG4 levels had not been assessed at the initial presentation or during the follow-up period before this examination. Differential diagnoses included meningioma, schwannoma, granulomatous disease, and inflammatory pseudotumor, with IgG4-related inflammatory pseudotumor considered the most likely diagnosis in light of the lesion's nerve-based extension and elevated serum IgG4 level. Owing to the lesion's progressive growth and the visual deterioration, a decision was made to perform a surgical biopsy. A left frontotemporal craniotomy was performed. After opening the Sylvian fissure, a schwannoma-like mass was identified on the cisternal segment of the oculomotor nerve (Supplementary Figure 1A). However, no obvious inflammatory or granulomatous changes were observed in the optic nerve itself. Intraoperative neurophysiological monitoring confirmed the presence of oculomotor nerve activity. A partial resection and biopsy of the lesion were performed. During the waiting period for frozen section analysis, bone decompression of the optic canal and superior orbital fissure was performed. The orbital roof, medial superior orbital wall, and anterior clinoid process were drilled to decompress the optic nerve. The dura overlying the optic nerve was incised longitudinally to achieve sufficient decompression. The superior wall of the cavernous sinus was opened to confirm tumor extension within the cavernous sinus (Supplementary Figure 1B). Intraoperative pathological diagnosis suggested an inflammatory pseudotumor. Therefore, no further resection was performed. Postoperatively, oculomotor nerve palsy with ptosis and extraocular movement disturbance developed in the patient, which was considered to be related to surgical manipulation. Histological analysis of the resected specimen revealed spindle cell proliferation with dense lymphoplasmacytic infiltration in a fibrotic stroma (Supplementary Figure 2A). S100 staining showed residual nerve bundles, with CD138-positive plasma cells identified (Supplementary Figure 2B). Immunohistochemistry revealed 25 IgG-positive plasma cells per high power field (HPF) (Supplementary Figure 2C) and 22 IgG4-positive plasma cells per HPF (Supplementary Figure 2D), with an IgG4/IgG ratio of 0.88. On the basis of histopathological and serological findings, the lesion was diagnosed as an IgG4-related inflammatory pseudotumor. Oral prednisolone (30 mg/day) was initiated postoperatively and tapered over 6 months. Follow-up MRI showed a significant reduction in lesion size (Supplementary Figure 3), and the serum IgG4 level normalized to 92.4 mg/dL. Oculomotor nerve function completely recovered; however, visual impairment was not alleviated.
Initial magnetic resonance T1 weighted gadolinium image (A) showing homogeneously enhanced masses that extended from left cavernous sinus involving superior orbital fissure. Follow-up axial (B) and coronal (C) images obtained 3 years later show interval enlargement of the lesion.
IgG4-related disease is a chronic, systemic immune-mediated disorder characterized by dense infiltration of IgG4-positive plasma cells accompanied by fibrosis in affected organs.6) First described in autoimmune pancreatitis,7) it is now recognized as a multisystem disorder involving nearly all organ systems.8,9) Among its various manifestations, IgG4-related inflammatory pseudotumor of the cranial nerves is particularly rare. To date, only 2 cases of IgG4-related inflammatory pseudotumor involving the cavernous sinus region with extension along the oculomotor nerve have been reported (Table 1),4,5) and the present case represents the third documented instance. Such lesions pose a significant diagnostic challenge because of their rarity and nonspecific radiological features. Linear or nodular enhancement along the course of the oculomotor nerve in the cavernous sinus region often leads clinicians to suspect more common entities, such as schwannoma or meningioma. In the present case, we further considered the radiological differential diagnosis of lesions arising around the oculomotor nerve, including schwannoma, meningioma, lymphoma, and granulomatous diseases. At the initial stage, the lesion was presumed to be a benign tumor, despite the presence of visual field impairment, which was the only neurological deficit at the time, and the relatively indolent course, which contributed to the decision to defer early intervention. The lesion revealed continuous extension along the anatomical course of the oculomotor nerve and showed homogeneous enhancement. These features may differ from the typical presentation of schwannomas, which often form well-circumscribed masses, in addition to meningiomas, which are frequently associated with dural attachment. Moreover, the findings were not entirely consistent with the diffuse infiltrative pattern commonly observed in lymphoma. Granulomatous diseases were also considered; however, the clinical course and imaging characteristics were not strongly suggestive. These considerations, along with the confirmation of elevated serum IgG4 levels, further support the radiological characteristics of IgG4-related inflammatory pseudotumor and help distinguish it from other entities. Although corticosteroid therapy yielded marked radiological regression, visual function did not recover. This unfavorable neurological outcome was most likely attributable to prolonged optic nerve compression before treatment initiation. Irreversible visual impairment may represent a characteristic feature of IgG4-related inflammatory pseudotumor involving the oculomotor nerve. This observation underscores the importance of early diagnosis and prompt initiation of treatment while also highlighting the potential limitations of visual recovery despite surgical intervention and corticosteroid therapy. These findings underscore a critical diagnostic pitfall: IgG4-related inflammatory pseudotumor may closely mimic benign nerve sheath tumors, and delayed recognition can cause irreversible neurological deficits despite favorable radiological response to medical therapy. From a surgical perspective, aggressive resection of lesions arising from cranial nerves carries a substantial risk of permanent neurological dysfunction. In this context, surgical intervention should be limited to targeted biopsy for diagnostic confirmation. Intraoperative neurophysiological monitoring was useful in confirming the neural origin of the lesion and enabling safe biopsy, thereby facilitating appropriate postoperative medical management.
Summary of Cases of Inflammatory Pseudotumor Involving the Oculomotor Nerve Reported in the Literature
| Case no. | Authors and year | Age/sex | Location | Initial symptoms | Diagnostic method | Treatment | Radiological response | Neurological outcome | Follow-up (months) |
|---|---|---|---|---|---|---|---|---|---|
| 1 | Le Marc’hadour et al. (4) (1994) | 40/Male | Cavernous-sinus extending to superior orbital fissure | Blindness | Partial removal | Steroid | Marked regression | No visual recovery | 24 |
| 2 | Tomio et al. (5) (2013) | 63/Male | Cavernous sinus-orbital region | Optic neuropathy | Biopsy | Steroid | Marked regression | No visual recovery | 9 |
| 3 | Present case (2026) | 56/Female | Cavernous sinus through superior orbital fissure to intraconal space | Blindness | Biopsy | Steroid | Marked regression | No visual recovery | 9 |
We reported a case of IgG4-related inflammatory pseudotumor involving the oculomotor nerve and causing optic nerve compression. IgG4-related disease should be considered in the differential diagnosis of unexplained lesions in the cavernous sinus-orbital region with oculomotor nerve involvement, and early biopsy-based diagnosis is crucial because timely corticosteroid therapy may prevent irreversible neurological damage.
All authors have no conflict of interest.
Informed consent was obtained from the patient for publication of this case report and accompanying images.
