An otherwise healthy 29-year-old female presented to the emergency room with diplopia from isolated cranial nerve VI palsy on the left and a history of left-sided headaches of several-month duration. Associated symptoms included pressure in the left ear and a "blocked" sensation. The patient did not complain of any vestibular symptoms. Otoscopy revealed normal tympanic membranes with no signs of middle ear pathology. Diagnostic audiometry revealed normal hearing and middle ear function. Normal blood investigation findings included fasting glucose, corrected calcium, magnesium, liver functions, thyroid functions, and a complete blood and platelet count. Serological testing, including human immunodeficiency virus (HIV) testing, treponema pallidum antibodies, anti-nuclear antibody (ANA) titers, and antineutrophil cytoplasmic antibody (ANCA) titres, was negative. Erythrocyte sedimentation rate (ESR) was 29, and C-reactive protein (CRP) was 14, mildly raised in both instances.
High-resolution computed tomography (HRCT) of the skull base demonstrated an aggressive erosive disease process centered on the left petrous apex involving the petroclival fissure and inferolateral clivus (Figure 1). Subsequent magnetic resonance imaging (MRI) revealed a trans-spatial marrow-replacing tumor-like soft tissue lesion of low T1/T2 signal (Figure 2A) and mild apparent diffusion coefficient (ADC) reduction. The lesion was enhanced avidly following gadolinium contrast administration (Figure 2B). Focal pachymeningeal thickening of the retroclival dura and enhancement of the cisternal segment of the left abducens nerve as it enters Dorello's canal were present.
The initial diagnosis favored Gradenigo syndrome, otomastoiditis, lateral rectus palsy, and deep facial pain, with a differential diagnosis of cholesteatoma, cholesterol granuloma, tuberculosis, mucocele formation, and petrous apex air cell effusion. The absence of signs of a systemic disease, clinically and later supported by pathology results, ruled out an infective process. Malignancies considered included chondrosarcoma, chordoma, plasmacytoma, multiple myeloma, paraganglioma, and meningioma. A tissue biopsy was required to make a definitive diagnosis.
Surgical access to the petrous apex includes the infracochlear, infralabyrinthine, middle fossa, and transsfenoid approaches. After studying the anatomy on the HRCT scans, the middle fossa approach was chosen as the most appropriate option.
Given the epicenter of the lesion, middle fossa craniotomy provided an elegant and effective means of approaching the lesion to obtain tissue for histological analysis. Nevertheless, the middle cranial fossa approach to the temporal bone can be considered invasive and is not without risks. However, by employing the transtemporal supralabyrinthine modification of the middle cranial fossa approach, described by Fisch, minimal retraction is placed on the temporal lobe. In the author's experience of more than 150 cases, the risk of developing epilepsy with this modification is minimal. Following the craniotomy, the petrous apex was identified, image guidance utilized to confirm and diamond burr drilling of the distorted petrous bone performed to access the lesion. The macroscopic appearance of the tissue was pink, firm, and without a clear capsule or vascularity (Figure 3). Numerous tissue biopsies were taken. The patient recovered well after the surgery without complications.
The microscopic examination of the biopsy fragments showed a dense lymphoplasmacytic inflammatory infiltrate with a fibrous background. Strands and vague fascicles of collagen fibers were also seen, as well as regions of focal storiform-type fibrosis. There was no evidence of obliterative phlebitis or granulomata. Fungal, bacterial, and mycobacterial stains were negative. A lymphoproliferative disorder was excluded. Immunohistochemical stains for IgG4 showed greater than 50 IgG4-positive plasma cells in some high-power fields (Figure 4). IgG4/IgG ratio was greater than 20%. These features were highly suggestive of IgG4-related disease.
Once the diagnosis was made, the patient was commenced on oral prednisone at 40mg daily to taper over a 6-month interval.
One month post-surgery, the patient complained of hoarseness. She was diagnosed with left vocal cord paralysis, with the affected vocal cord in the paramedian position. MRI revealed an extension of the original disease process, and the MRI of the neck was normal. In the light of the MRI findings, the paralysis of the recurrent laryngeal nerve was thought to be due to IgG4-related peripheral axonal neuropathy.
Three months after the post-procedure, the patient continued on prednisone. The left cranial nerve VI palsy and vocal cord paralysis have resolved entirely. The patient returned to work with an occasional complaint of blurred vision. Concerns exist that upon discontinuation of prednisone, she will experience symptom recurrence.