Fig. 4.1
Jugular paraganglioma arises from the jugular bulb. It frequently involves the surrounding bone and extends to the hypotympanum through the Jacobson’s canal (black arrow, a). Bone destruction is a well-documented CT characteristic of skull-base tumors. J-PGL classically causes an erosive or permeative pattern at a late stage. Typical extensions are shown in (a–d). This figure highlights the different patterns of extension with increasing bony erosion involving the hypotympanum, mesotympanum, infracochlear area, tympanal bone, and sulcus tympanicum
The goal of the imaging is:
- 1.
To narrow the differential diagnosis. The most frequent lesions in the jugular foramen region are jugular paraganglioma (60–80%), schwannoma/neuromas, and meningiomas (both approximately 10%) [2]. Rarely, primary bone (giant cell tumor, chondrosarcoma, and chondroblastoma) and masses within the subarachnoid space (epidermoid cyst) can also affect this region. Jugular foramen metastasis and pseudotumor have been described as well as dehiscent jugular bulb [3].
- 2.
To define the extension of the lesion. Multidetector CT angiography (MD-CTA) has expanding capabilities including isotropic multiplanar reconstruction, improved temporal and spatial resolution, and angiographic analysis [2]. The same exam can assess bony erosion, tumor extension, and contrast agent uptake at the arterial and venous phases.
CT is the best exam to look at the normal anatomy of the jugular foramen. The lateral (pars vascularis) and medial (pars nervosa) can be well defined and compared to the healthy side. The intrajugular process which is typically dividing these two compartments can be visualized if ossified. It joins the jugular process of the occipital bone to the jugular spine of the petrous temporal bone. Both of these structures can be eroded by the lesion. The analysis of the tumor in the coronal plane allows to distinguish between hypotympanic and tympano-jugular forms of paraganglioma which is of the utmost importance in the treatment plan. CT is able to detect an erosion of the carotid canal, the fallopian canal, the ossicles, and the inner ear. Irregular erosive enlargement of the jugular foramen is typical of a jugular paraganglioma. Suggestive CT findings include jugular foramen enlargement (length plus width >20 mm) predominantly involving the pars nervosa with irregular bony margins and erosion of the jugular bulb and vascular crest. In contrast, jugular foramen schwannomas are well-circumscribed tumors that tend to push rather than invade structures. Thus, bony changes typically demonstrate an enlarged foramen with more regular and smooth margins. The mean radiodensity of J-PGL is 210 HU compared with 69 HU for neuromas [4]. Of note, some critical area should be assessed from the beginning since less than 1 mm growth may be sufficient to hamper the prognosis (e.g., facial nerve, cochlea, CPA angle) (Figs. 4.2 and 4.3). The association of MRI imaging alongside contrast uptake timing with CT angiography can more accurately characterize the lesion (Fig. 4.4).
Fig. 4.2
The extension in the area surrounding the fallopian canal is determined using reconstruction along the course of the intratympanic and mastoid segment of the facial nerve from high-resolution temporal bone CT imaging. (a) left temporal bone CT-scan. Intact fallopian canal. (b) left temporal bone CT-scan. Hypotympanic tumor and decreased density of the bone surronding the fallopian canal. (c) right temporal bone CT-scan. erosion of the surronding bone respecting fallopian canal. (d) right temporal bone CT-scan. Bone destruction affecting the fallopian canal
Fig. 4.3
Progressive erosion of the fallopian canal during the follow-up of a SDH-D-related jugular paraganglioma. Note the increasing erosion at risk of epineural spread
Fig. 4.4
Epineural spread of a jugular foramen paraganglioma in a SDH patient revealed by a facial paresis associated with conductive hearing loss. (a) Axial post-contrast T1 MR imaging showing intense gadolinium uptake of a tumor surrounding the facial nerve. (b) Axial high-resolution CT scan of the temporal bone showing bony erosion of the tumor raising from the jugular foramina and extending to the mastoid. (c) Involvement of the facial nerve at the stylomastoid foramina. (d) Surgical view of the mastoid segment of the facial nerve (FNm) with edematous change (black asterisk: lateral semicircular canal). (e) The facial nerve is freed off of tumor at the stylimastoid foramina (S-MF). (f) The facial nerve is preserved and anteriorly rerouted for further tumor resection (T)
CT Angiography (Figs. 4.5 and 4.6)
At the authors’ center, helical CT angiography is performed to allow 3D reconstruction on a Philips Brilliance 40-slice scanner. Acquisition comprises a double spiral with arterial and venous phases using the following parameters: pitch, 1; table speed, 2 mm/s; slice thickness, 0.6 mm; and reconstruction every 0.3 mm, acquisition time (variable as a function of the number of rows), 120 kV, 250 mAs. Contrast agent is injected by a power injector with the following parameters: 120 cc to 3 cc/s and then 30 cc to 1 cc/s and start time of 30 s for the first arterial spiral and 70 s for the second venous spiral. Vessels are well opacified during the two acquisitions with this type of injection. For tumors with arterial contrast enhancement, such as paragangliomas, the first spiral will be used for reconstruction, while, for tumors with later contrast enhancement (meningiomas or neuromas), the second spiral will be used for reconstruction [1]. With this workup, CT angiography avoids the need to perform invasive catheter angiography for diagnostic purpose. Christie et al. found that the mean radiodensity of the paragangliomas was 210 HU (range 117–371 HU) compared with 69 HU (range 58–98 HU) for the neuromas when using a MD-CTA (64-slice CT scanner system (Philips Medical Systems, Cleveland, OH, USA)) with 120 kV and 400 mAs and 60 ml of contrast medium (Iobitridol, 350 mg iodine/ml; Xenetix, Guerbet, Roissy, France). Since both arterial and venous uptakes are necessary, imaging was started 40 s after the start of the contrast medium injection. The pitch was set at 0.891 with a detector configuration of 4 1.25 or 64 0.625 mm. A 50% overlap of the reconstructed axial sections was achieved with a section width of 1 mm and 0.5 mm increment (Fig. 4.7).
Jugular vein analysis on CT angiography (compression, occlusion, tumor infiltration) brings up important information when a surgical treatment is scheduled. This can influence the surgical planning (e.g., sacrifice of the jugular vein to ensure adequate tumor removal) (Fig. 4.5c, e, f). If computer-assisted navigation is scheduled for surgery, a dedicated CT evaluation is required to ensure the best possible registration (Fig. 4.8).
Fig. 4.5
Venous anatomy relevant to J-PGL (FN, facial nerve; T, tumor; iPS, inferior petrosal sinus; ICA, internal carotid artery; SS, sigmoid sinus; CV, condylar vein; EV, emissary vein; OV, occipital vein). (a) Surgical view during the opening of the jugular bulb. The J-PGL is involving the outer part of the vein and the medial plane is free of tumor. Note the opening of the inferior petrosal sinus medially to the tumor. (b) Inferior petrosal sinus may be enlarged on the side of the tumor. It is important to assess its volume prior to surgery since it may be a source of an important bleeding. (c) Intraluminal extension of the J-PGL into the inferior petrosal sinus. This extension might be difficult to safely resect during surgery since it would hamper the functional prognosis of the lower cranial nerves. (d) The hypoglossal canal should as well be assessed since it may provide collateral venous drainage to the tumor that can be exposed to increased bleeding during surgery when dissecting the medial wall of the internal carotid artery. (e) Collateral drainage through the condylar vein. (f) Collateral drainage through the emissary vein and occipital vein
Fig. 4.6
Internal carotid artery (ICA) involvement assessed using CT angiogram with 3D reconstruction. (a and b) Internal carotid artery thrombosis, (c and d) extension of the J-PGL spreading in the adventitia of the ICA (T, tumor; black arrows, tumor removal is obtained by developing the plane in the vessel adventitia), and (e and f) adhesion of the J-PGL at the posterior border of the ICA. During surgery, the posterior limit of the ICA is easily identified with limited exposure and progressively freed off of tumor (modified Fisch technique without facial nerve rerouting and partial external auditory canal (EAC) resection eligible for reconstruction of the EAC)
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