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Symptoms

Dizziness and IAC Lesion

Djalilian, Hamid R. MD

doi: 10.1097/01.HJ.0000538932.32376.c7
Clinical Consultation
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Dr. Djalilian is the director of neurotology and skull base surgery and a professor of otolaryngology and biomedical engineering at the University of California, Irvine.

A 51-year-old woman came in for an evaluation of dizziness. She had had recurrent attacks of vertigo over the past two years. The attacks lasted approximately two to three hours, and were accompanied by ear and head pressures. Between the episodes, she was completely normal. She had no history of ear surgery or head trauma. Examination of her ear showed normal tympanic membranes. The patient's audiogram was also normal, and the CT scan of her temporal bone showed a possible lesion posterior to the internal auditory canal (IAC) on the left ear. The possible lesion had eroded the posterior bony wall of the IAC, and was in contact with the IAC dura.

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Diagnosis: Vestibular Migraine High-riding Jugular Bulb/Jugular Bulb Diverticulum

Patients presenting with episodic dizziness require an evaluation independent of imaging findings. Clinicians have a tendency to associate imaging findings with a patient's symptoms. However, it should be kept in mind that a fixed lesion seen on imaging is more likely to cause constant symptoms. It is unlikely that a lesion that continuously puts pressure on structures related to balance, such as the vestibular nerves or the brain stem/cerebellum, would cause symptoms that would come and go and leave the patient asymptomatic between episodes. In the case of a mass lesion, a more likely scenario would be that the patient will experience constant imbalance, dizziness with head movements, etc. In our experience, we have found that even patients with an acoustic neuroma and intermittent vertigo episodes usually have vestibular migraine. These patients responded well to migraine prophylactic therapy and lifestyle changes; their symptoms eventually resolved (Otol Neurotol. 2017 Dec;38(10):e457).

Figure 1 shows a possible lesion posterior to the left internal auditory canal. On the inferior side, there was greater encroachment on the internal auditory canal (IAC; Fig. 2). The bony walls around the lesion were sharp, indicating a benign process. Malignant lesions tend to infiltrate the bone, causing a destruction. The borders around malignant lesions are not sharply demarcated. A glomus jugulare tumor infiltrated the bone and appears on a CT scan without any clear border around the jugular bulb. This created the appearance of an ink blotch (in reality, a tumor). Following the lesion more inferiorly and looking at the coronal and sagittal imaging (see patient videos 1-3 online or in our iPad app), the lesion in question appeared to be a very high-riding jugular bulb.

The MRI of the IAC also showed no compression of the vestibular nerves. The nerves were best seen on the T2 (Fig. 3) or CISS/FIESTA/3D MPR (Fig. 4) sequences. In these sequences, the cerebrospinal fluid appeared bright (white) and the nerves appeared gray. While the CT scan showed that the anterior posterior dimension of the IAC was compromised, the MRI did not show any mass effect on the nerves. While the anterior-posterior dimension of the IAC can be as small as 3 mm, it would still leave enough space for the cerebrospinal fluid and the 1mm-wide nerves to traverse the canal without compression. The T1 post-contrast MRI (Fig. 5) showed that the jugular bulb was very close to the structures of the IAC. However, by coordinating these findings with those of the T2 (Fig. 3) and CISS (Fig. 4) sequences, no compression was seen. It is important to look at patient imaging in its totality and review all relevant sequences. In this case, looking at the CT scan alone could create the impression that there was nerve compression in the IAC, which can lead to unnecessary interventions. However, a thorough review of the patient's MRI scans showed no compression.

Venous blood intracranially drains into the dural venous sinuses. Unlike veins that are found in the arms and legs, venous sinuses do not contain valves that slowly move the blood against gravity toward the heart. Venous sinuses are infoldings of the dura containing venous blood that drains from the brain to the heart. The largest of these sinuses is the superior sagittal sinus that runs in the midline of the skull. Most commonly, the superior sagittal sinus drains into the right transverse sinus, which then drains into the sigmoid sinus that runs posteriorly in the mastoid. The sigmoid sinus turns into the jugular bulb, which also receives venous blood from the inferior petrosal sinus. Because of the preferential drainage of the superior sagittal sinus into the right-sided venous sinus system, the jugular bulb on the right side is larger than the one on the left in 70 percent of patients. Therefore, a case of pulsatile tinnitus that is venous in origin occurs more commonly on the right side.

The jugular bulb is normally positioned below the posterior aspect of the middle ear cavity. Though uncommon, the jugular bulb on one side may become very large and ride superiorly, well into the middle of the ear space or against the tympanic membrane. In such cases, the contact of the jugular bulb against the tympanic membrane can cause conductive hearing loss and pulsatile tinnitus (Laryngoscope. 2013 Jul;123(7):1803).

A higher-riding jugular bulb that is in contact with the tympanic membrane can be repaired surgically by moving the inferior aspect of the tympanic membrane more laterally. The jugular bulb itself is very fragile, and manipulation of the bulb will invariably lead to bleeding from micro tears in the wall. The jugular bulb rarely extends to the IAC, and when it does, symptoms that are associated with pulsatile tinnitus, not vertigo, would usually manifest. This anomaly could be problematic if a skull base surgery is contemplated.

This patient's vertigo was thought to be caused by vestibular migraine. She underwent migraine prophylactic therapy, made lifestyle changes, and eventually got good results. The key factors considered in determining the association of the patient's vertigo with migraine were the episodic nature of the incidences, the lack of symptoms between the episodes, and the concurrent aural and head pressures. While diagnosing a migraine does not necessarily require the presence of headaches, this patient happened to have head and aural pressure symptoms during episodes (Otolaryngol Head Neck Surg. 2018 Jan;158(1):100).

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iPad Exclusive!

BONUS VIDEOS: VISUAL DIAGNOSIS

Read this month's Clinical Consultation case, then watch the accompanying videos from Hamid R. Djalilian, MD, to review the patient's imaging for yourself.

  • Video 1. Axial (horizontal) CT of the left temporal bone showing the area posterior to the IAC.
  • Video 2. For comparison: Axial CT of the right temporal bone showing the jugular bulb in its normal position below the middle ear.
  • Video 3. Coronal (vertical) CT of the left temporal bone in the plane of the posterior semicircular canal showing the jugular bulb in its course.
  • Video 4. Poschl view CT (parallel to the superior semicircular canal) of the left temporal bone showing an intact superior semicircular canal.
  • Video 5. Axial T2-weighted MRI of the temporal bones showing the IACs with cerebrospinal fluid and indicating no compression.
  • Video 6. Axial T1-weighted post-contrast MRI of the brain that shows the jugular bulb abutting the IAC, which can be misinterpreted as an appearance of an enhancing tumor.

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