Traversing the cavern: radiological manifestations of cavernous sinus pathologies

Abstract

Background

Owing to their peculiar location, cavernous sinuses communicate with numerous head and neck structures via fissures and foramen which provide an easy access for pathologies to traverse to and from the cavernous sinuses to these vital structures. On routine brain imaging, diseases involving the cavernous sinuses can be easily missed if we are not vigilant to examine cavernous sinuses using dedicated thin sections of sellar and parasellar region.

Main body of the abstract

The various pathologic conditions involving cavernous sinuses either primarily or secondarily include neoplasms, vascular conditions, cystic/fat-containing lesions and infective/inflammatory conditions. Due to considerable overlap in clinical symptoms of numerous diseases affecting cavernous sinuses, timely and effective imaging evaluation of cavernous sinuses using multimodality approach with dedicated imaging sequences can help in formulating a clinically relevant differential diagnosis and alter patient management. Thin T1- and T2-weighted axial and coronal images with appropriately timed MR angiography and venography should be performed for diagnosis of cavernous sinus pathologies and delineation of pathologies arising from closely placed neurovascular structures in this region of middle cranial fossa. In this review article, we aim to discuss how to best image the cavernous sinuses for detection of cavernous sinus pathologies and imaging appearance of various pathologies involving cavernous sinuses.

Conclusion

Cavernous sinuses form an important pathway for spread of numerous pathologies to and from the intracranial compartment to nearby vital structures. A variety of conditions can affect these small paired venous structures including benign and malignant neoplasms, vascular lesions, and infective/inflammatory pathologies. It is therefore important that besides routine brain imaging, dedicated thin axial and coronal images along with contrast-enhanced imaging should be performed for diagnosis of cavernous sinus pathologies.

Background

Cavernous sinuses are extradural venous structures lying on either side of the sphenoid sinus and sella and communicating with various head and neck structures via fissures and foramen [1]. They are affected by numerous disease processes arising within the cavernous sinuses or extending from surrounding structures into the sinus. Most of the pathologies have similar presenting complaints including painful ophthalmoplegia, proptosis, chemosis, vision loss, and headache, rendering imaging an essential part of evaluation of cavernous sinus pathologies. A thorough literature search was done using published papers in PubMed, ScienceDirect, and Google Scholar databases to find a variety of publications on the cavernous sinus anatomy and pathologies. In this review article, we discuss the various pathologic conditions including neoplasms, tumor-like conditions and cystic lesions, vascular lesions, and infective/inflammatory conditions which may involve cavernous sinuses either primarily or secondarily. Various imaging findings that help to formulate a clinically relevant differential diagnosis have also been discussed.

Main text

Methodology

Multiple methods were used to find a variety of publications on the cavernous sinus anatomy and pathologies. Medline was searched for “Cavernous sinus [MeSH]”, “Carotid-cavernous sinus fistula [MeSH],” “Cavernous sinus thrombosis [MeSH]” and “Cavernous sinus syndrome[MeSH]” to retrieve papers that were published on pathologies of cavernous sinus. Published papers in PubMed, ScienceDirect, and Google Scholar databases were used to search for original articles, reviews, and case reports in English between 2000 and January 2024. References of the articles were screened for other papers and included in this review when considered relevant. The inclusion criteria were published papers describing anatomy and pathologies involving the cavernous sinus.

Anatomy

Cavernous sinuses are paired venous sinuses, which are situated on the lateral aspect of the midline structures (including sphenoid sinus, sella turcica, and pituitary gland) and medial to the bilateral medial temporal lobes. The name "cavernous" was first given by Winslow due to the presence of numerous fibrous septae within the sinuses, which renders them a cavern-like appearance. Due to their unique placement, cavernous sinuses communicate with the surrounding structures including the orbits, the pterygopalatine fossa, the nasopharynx, and the middle and posterior cranial fossae via various fissures and foramen [1]. They are also interconnected with each other via anterior and posterior intercavernous channels. Thus, pathologies may traverse to and from the cavernous sinuses to these surrounding vital structures.

They consist of five walls, i.e., medial, lateral, anterior, posterior, and a roof. The medial wall is a single layer of dura, whereas the rest of the walls have a double layer of dura, rendering an extradural location to these sinuses. Anteriorly, they extend to superior orbital fissures and are limited posteriorly by prepontine cisterns. The inferior boundary is formed at the meeting point of the lateral and medial walls.

The cavity of cavernous sinuses is continuous with the epidural space of the spine and orbit and contains the abducens nerve (cranial nerve VI), internal carotid artery (ICA) along with peri-carotid sympathetic plexuses [2]. Along the lateral wall of the sinus run the oculomotor nerve (cranial nerve III), the trochlear nerve (cranial nerve IV), the ophthalmic nerve (cranial nerve V1), and the maxillary nerve (cranial nerve V2) arranged in that order from superior to inferior (Figures 1 and 2). These nerves traverse between the two layers of dura that form the lateral wall of cavernous sinuses, allowing the surgeons easy extra-sinus access. The internal carotid artery (ICA) has a sigmoidal intrasinus course, consisting of five segments, including a posterior vertical segment, posterior genu, horizontal segment, anterior genu, and anterior vertical segment [3]. Major tributaries of the sinus include superior and inferior ophthalmic veins. Important draining veins include the superior & inferior petrosal sinuses which drain into the basilar plexus.

Fig. 1

Normal cavernous sinuses on MRI. A Line diagram of coronal section through cavernous sinuses showing neurovascular structures and their relations. Lumen of cavernous sinus contains internal carotid artery, cranial nerve VI and sympathetic plexus around internal carotid artery. The lateral dural wall is split into two and contains cranial nerves III, IV, V1 and V2 in that order from superior to inferior. B Coronal T2W image shows the medial wall (red arrow), lateral wall (green arrow), floor (yellow arrow) along with intracavernous ICA (blue arrow) seen as a flow void. C Post contrast fat-saturated coronal T1W image shows cranial nerves III-V as tiny hypointense foci along the lateral dural wall (dotted circle). Cranial nerve VI is seen as a single hypointense focus just inferior to ICA (dashed arrow)

Fig. 2

Normal cavernous sinuses on CT. Axial (A) and coronal (B) CECT images reveal normal symmetrical homogeneous enhancement of bilateral cavernous sinuses (white arrows). Coronal bone window (C) image shows the osseous relationship of cavernous sinus with its medial wall abutting the lateral wall of sphenoid sinus (red arrows). Note foramen rotundum (yellow arrows) bilaterally through which maxillary nerve passes into the pterygopalatine fossa

Clinical presentation

Cavernous sinus syndrome refers to various clinical signs and symptoms related to the pathologies within or adjacent to the cavernous sinus [4]. The classic clinical manifestations include total or partial ophthalmoplegia, exophthalmos, Horner syndrome (characterized by miosis, ptosis, enophthalmos, anhidrosis, and loss of cilio-spinal reflex), and facial pain with/without facial sensory loss, and headache [2]. Pathologies involving the anterior part of the cavernous sinuses usually present with ophthalmoplegia and further extension into the orbital apex leads to blurring or loss of vision [5]. The symptoms can either be insidious (usually with neoplastic and chronic inflammatory causes) or sudden (with acute inflammatory and vascular causes) in onset, but considerable overlap exists between the two; therefore, early diagnosis may help salvage sight and even life [6]. Hence imaging plays an indispensable role in early identification of the underlying pathology. Both CT and MRI have been used to evaluate cavernous sinuses but the excellent soft tissue contrast inherent in MR imaging makes it the imaging modality of choice with CT being useful for assessing osseous abnormalities.

Imaging protocol

A routine brain imaging including T1-weighted, T2-weighted, FLAIR and diffusion-weighted sequence should be performed before dedicated imaging of the cavernous sinuses. MRI protocol for cavernous sinuses includes coronal T2-weighted sequence, fat-suppressed, and post-contrast T1-weighted sequences in the axial and coronal planes with a slice thickness of <3mm. Additionally, a 3D CISS/FIESTA/DRIVE sequence may be acquired for better delineation of neural anatomy and adjacent cisterns. The field of view should extend from orbits anteriorly to the brainstem posteriorly (Table 1). Multidetector CT with a thin section (<1mm) axial acquisition and multi-planar reconstruction is quite useful to study the osseous relationship of sinus lesions. CT angiography performed with bolus-track technique or MR angiography both non-contrast TOF sequence or post-contrast sequence can help in assessing the relationship between cavernous sinus lesions and ICA along with evaluation of vascular lesions of cavernous sinuses. In cases with suspicion of cavernous sinus thrombosis, a delayed scan (at least 45 seconds after contrast injection) should also be preferably acquired [6]. Digital subtraction angiography has an important role in the diagnosis and interventional treatment of vascular disorders.

Table 1 MR imaging protocol for cavernous sinus pathologies

Thin section heavily T2-weighted coronal, thin section T1 weighted with and without fat saturation and post-contrast imaging are the cornerstone sequences for formulating a diagnosis. FLAIR and diffusion-weighted imaging acquired as part of routine brain imaging aid in distinguishing between arachnoid cyst and epidermoid cyst with former showing complete suppression on FLAIR and no diffusion restriction while the later shows partial suppression on FLAIR and marked diffusion restriction.

Pathologies

Cavernous sinuses may be affected by a variety of pathologies including neoplasms (benign or malignant), cystic lesions, vascular conditions, and inflammatory/infectious pathologies.

Neoplasms

Neoplasms that involve the cavernous sinuses can be primary, i.e., arising within the cavernous sinuses, or secondary, i.e., arising from adjacent structures and invading the cavernous sinuses later. Metastatic or hematological pathologies are also included in the secondary neoplasms of cavernous sinuses.

Primary neoplasms

Meningiomas

Meningiomas arise from arachnoid cap cells of the dura and are the commonest tumors to involve cavernous sinuses. Meningiomas are more commonly seen in females in the 5th-7th decade possibly due to hormonal effects and can be solitary or multiple. Multiple meningiomas are indicators of syndromic associations most commonly neurofibromatosis type 2. Being predominantly low-grade (WHO grade I) tumors, meningiomas are usually well-circumscribed extraxial masses, though a small fraction can be WHO grade II/III, which are associated with increased mitotic index, anaplasia, brain invasion, and necrosis. Owing to increased cellularity and calcification, they appear iso to hypointense with respect to cortical gray matter on T1- and T2-weighted images and show diffusion restriction along with homogenous post-contrast enhancement with an enhancing dural tail which can either be reactive or due to tumor invasion [7]. Hyperostosis of adjacent bony structures and calcification, associated with meningiomas are better evaluated on CT (Figure 3). Meningiomas invading the cavernous sinuses can also encase the cavernous segment of the ICA, causing its narrowing, or invasion of its wall which can help to differentiate it from pituitary macroadenoma as the latter does not cause narrowing of ICA. Invasive tumors tend to be more heterogeneous likely due to increased vascularity, cystic changes, and associated areas of hemorrhages. They are associated with an increased incidence of brain and adjacent osseous tissue invasion.

Fig. 3

Sphenoid wing meningioma with cavernous sinus involvement. Axial T2W (A) and post-contrast fat-suppressed axial (B) and coronal (C) T1W images in a 56-year-old female patient, show a T2 hypointense extra-axial mass lesion in left middle cranial fossa (white arrows) and cavernous sinus showing homogenous enhancement. The left ICA is displaced medially with normal flow void (red arrows). Note adjacent left sphenoid bone hyperostosis (blue arrows) and dural tail (green arrow)

Schwannomas

Schwannomas are the second most common neoplasms involving the cavernous sinus. They are also called neurinomas, and most of them arise from the trigeminal nerve and rarely from other neural structures in the cavernous sinus. These tumors can either be sporadic or syndromic (most commonly neurofibromatosis type 2). Sporadic tumors are mostly solitary and usually present in the 5^th or 6^th decade of life, whereas multiple tumors are seen at a comparatively younger age with syndromic association. A typical dumbbell shape can be appreciated when they extend to the posterior cranial fossa, infratemporal fossa, or to the orbits due to constriction at narrow foraminal sites, whereas, the tumors involving only cavernous sinus proper appear ovoid. On histology, these tumors are mainly composed of spindle cells, and based on cellular arrangement, two patterns are described, i.e., Antoni A and Antoni B pattern. Antoni A pattern has a compact arrangement of cells, whereas Antony B pattern has a loose cellular arrangement rendering it prone to cystic degeneration. Often, these tumors are difficult to visualize on unenhanced CT, as the cellular component appears mostly isodense to the brain parenchyma; however, the associated cystic component helps in its identification. These tumors are very slow-growing and are associated with adjacent smooth bone remodeling which may be in the form of foraminal widening. On MR, they are iso-hypointense to gray matter on T1-weighted images, heterogeneously hyperintense on T2-weighted images with no significant diffusion restriction [8]. The cystic component appears hypointense on T1-weighted images with marked hyperintensity on T2-weighted images, thus imparting a heterogenous appearance to the tumors. On post-contrast images, owing to their cellular arrangement, Antoni A pattern areas appear more homogeneously enhancing while Antoni B pattern areas show heterogenous enhancement (Figure 4). It is not uncommon to find areas of hemorrhage associated with these tumors resulting in fluid levels within cysts of tumors. In long-standing tumors, hemosiderin stains can be appreciated on T2* images due to chronic episodes of bleeding. Dumbbell shape, heterogeneous appearance, and no diffusion restriction seen in schwannomas help differentiate them from meningiomas.

Fig. 4

Trigeminal schwanomma. Axial T2W (A), coronal FLAIR (B) images in a 55-year-old male patient show an oval heterogeneously hyperintense lesion in the right cavernous sinus (red arrows) closely abutting right ICA (green arrow) which shows normal flow void. Axial post-contrast T1W (C) image shows minimal heterogenous enhancement of the lesion (yellow star). The relationship of the mass to the trigeminal nerve is well demonstrated on the axial 3D CISS image (D) with the nerve seen eccentrically along the posterolateral aspect of the tumor( white arrow)

Plexiform neurofibromas

Plexiform neurofibromas are benign WHO Grade I tumors that arise from peripheral nerve sheath. They arise commonly from the ophthalmic and maxillary divisions of the trigeminal nerve and are exclusively seen with neurofibromatosis type I and present at an early age when compared to other lesions. They appear as ill-defined hypodense masses on unenhanced CT, hypointense on T1-weighted images, showing characteristic “target sign” with central hypointensity (attributed to the dense collagenous stroma) and peripheral hyperintensity on T2-weighted images (due to myxoid matrix) [6, 8]. Although commonly seen in neurofibroma, this sign is not specific and can be seen in other nerve tumors like schwannoma. They show minimal post-contrast enhancement on CECT, which is better appreciated on post-contrast MR images. The presence of other stigmata of neurofibromatosis type 1 like café au lait spots, sphenoid wing dysplasia, optic nerve glioma, ocular hamartomas, inguinal freckles, etc. can help arrive at the diagnosis when the imaging diagnosis is uncertain. Malignant transformation although rare can be seen in a few cases where the lesions show rapid growth with infiltrative margins, bone erosions, increased enhancement, peritumoral edema, and heterogeneity with loss of T2 target sign.

Neoplasms secondarily involving the cavernous sinuses

Neoplasms arising from the sellar/suprasellar region, nasopharyngeal/sinonasal region, skull base, orbital region, or adjoining brain tumors can secondarily involve cavernous sinuses.

• (1) Sellar/suprasellar neoplasms: Sellar and suprasellar neoplasms that are most commonly associated with cavernous sinus invasion include pituitary adenomas, craniopharyngiomas, and germ cell tumors.

  • (A) Pituitary Adenomas- Pituitary adenomas are one of the most common tumors to secondarily involve cavernous sinuses. These along with pituitary carcinomas are together referred to as PitNET i.e., pituitary neuroendocrine tumors. They are commonly seen in the adult age group and can be divided into macroadenomas(> 1 cm) and microadenomas (< 1 cm) based on the tumor size. The former are commoner and more commonly invade cavernous sinus, sphenoid, or clivus and are referred to as invasive macroadenoma. The tumor appears isointense to hypointense on T1-weighted images, heterogeneously hyperintense on T2 weighted with heterogenous post-contrast enhancement. Larger and more aggressive tumors tend to be more heterogeneous owing to increased vascularity, cystic changes, and associated areas of hemorrhages. When compared to meningioma, the adenomas rarely show calcific foci. Extension of tumors beyond the lateral layer of the pituitary gland’s dural sac suggests invasion; however, it is very difficult to appreciate this thin dural layer even on MRI. Therefore, many indirect signs that suggest cavernous sinus invasion have been described. In a method devised by Knosp et al., three lines, i.e., medial carotid, median carotid, and lateral carotid lines, were used to show the extension of the tumor into the cavernous sinus with respect to the ICA [9] (Fig. 5). It is mandatory to correctly identify cavernous sinus invasion preoperatively because of the associated increased incidence of vascular injury and CSF leak. Pituitary carcinoma has a similar appearance as that of macroadenoma but differs in having CSF dissemination or evidence of other metastatic sites by definition.

    Fig. 5

    

    Invasive pituitary macroadenoma with bilateral cavernous sinus involvement. Coronal T2W (A), post-contrast fat-suppressed T1 W coronal (B) and sagittal (C) images in a 52-year-old female patient with complaints of headache and vision loss (L > R) show a homogenously enhancing (star in B and C) isointense mass involving pituitary gland with extension to bilateral cavernous sinuses (yellow arrows in A and B), sphenoid sinus (blue star in C), suprasellar region, along with involvement of optic chiasm (blue arrow in B). There is associated hydrocephalus and encasement of bilateral ICA which however, show normal flow voids (red arrows in B)

  • (B) Craniopharyngiomas- According to the 2021 WHO central nervous system tumors classification, adamantinomatous and papillary craniopharyngiomas are two distinct tumor types with the former arising along the craniopharyngeal duct and later arising along the hypothalamic-pituitary axis, often in the region of infundibulum or floor of third ventricle [10]. Larger tumors are associated with cavernous sinus invasion, optic chiasm distortion, and obstructive hydrocephalus [6, 11]. Adamantinomatous craniopharyngiomas have bimodal age distribution with peaks in the 2nd and 5th-6th decade and can occur in sellar or suprasellar locations. They are associated with cystic component, calcification, and enhancement of cyst wall and solid components (Fig. 6). Foci of T1 hyperintensity owing to cholesterol and keratin components are also seen and were historically known as motor oil cysts. They are locally aggressive, show adhesion with adjacent structures, and tend to recur after resection. Papillary craniopharyngiomas occur in adults and typically appear as solid spherical tumor in the suprasellar region. They do not show T1 hyperintense component, either lack or show minimal cystic changes with relatively uncommon calcification and intrasellar involvement.

    Fig. 6

    

    Adamantinomatous craniopharyngioma. Axial (A) and coronal (B) T2W images in a child show a large heterogenous solid cystic suprasellar mass lesion with fluid–fluid levels within the cystic component (red arrow in A). The lesion is extending into sella, anterior (white star in A), bilateral middle (yellow star in A) and posterior (blue star in A) cranial fossae. Bilateral cavernous sinuses are also involved (arrow in B). Mass effect is seen in form of hydrocephalus. Post-contrast axial (C) and coronal (D) images show heterogenous and avid enhancement of the solid component (green star in C and D)

  • (C) Germ cell tumors: Intracranial germ cell tumors are commonly seen in the pineal and suprasellar locations. They usually occur in younger patients (< 20 years). Germinomas appear more solid when compared to other germ cell tumors which are associated with more cystic components and tend to be more invasive. Intense homogenous post-contrast enhancement can be seen. Tumor markers including AFP and beta-hCG (raised in germinomas) can help in pointing toward the diagnosis. Teratomas usually do not pose a diagnostic challenge owing to the presence of both fatty and calcific components [11].

• (2) Nasopharyngeal/sinonasal neoplasms: Juvenile nasal angiofibromas are the most common nasopharyngeal neoplasms involving cavernous sinuses.

  • (A) Juvenile Nasopharyngeal Angiofibromas- Juvenile nasopharyngeal  angiofibromas are benign but locally aggressive tumors, exclusively seen in young male adolescents. Being highly vascular tumors, patients mostly present with recurrent episodes of spontaneous epistaxis. The classical site of occurrence is in the sphenopalatine foramen and involvement of the cavernous sinus is usually secondary to skull base erosion or via extension through the skull base foramen. They show a lobulated appearance on imaging and result in the expansion of the pterygopalatine fossa and pterygomaxillary fissure. These tumors can also cause anterior bowing of the posterior wall of the maxillary sinus (Holman-Miller antral sign) which is very well appreciated on CT images (Fig. 7). Other bony changes like erosions, fissural, and foraminal widening can also be better demonstrated on CT images. Intracranial extension of tumors renders them stage III (according to the staging system by Sessions et al. and Radkowski) [12]. The tumors show intermediate signal intensity on T1-weighted images and hyperintensity on T2-weighted images. Flow voids can also be easily appreciated on T2-weighted images owing to their high vascularity. These flow voids give a salt and pepper kind of appearance to the tumor on T2-weighted MR images where the voids appear as black pepper and acute bleed as white salt. Intense and homogenous post-contrast enhancement is a rule. It is of paramount importance to identify the vascular supply of these tumors so that preoperative embolization can be carried out to reduce the chances of major intraoperative bleeding episodes. CT Angiography is the modality of choice. Most of the tumors (80%) receive their vascular supply from branches of the external carotid artery i.e., internal maxillary, ascending pharyngeal, and palatine arteries. A minor proportion (20%) of cases can receive their supply from branches of the internal carotid artery i.e., sphenoidal and ophthalmic branches [13].

    Fig. 7

    

    Juvenile nasopharyngeal angiofibroma. Axial (A) and coronal (C) CECT images in an adolescent male patient with recurrent epistaxis, show an avidly enhancing mass lesion (white arrows) involving nasopharynx, nasal cavity, left pterygomaxillary fissure which is widened (green arrow), left infratemporal fossa, sphenoid sinus, and left cavernous sinus (red arrow) via skull base erosion better seen on the axial (B) and coronal (D) bone window images. Remodeling of the adjacent bones and anterior bowing of medial walls of bilateral maxillary sinuses is also seen—Holman miller sign (yellow arrow)

  • (B) Nasopharyngeal and sinonasal malignancies- Malignant tumors arising in this region including nasopharyngeal carcinoma, various sinonasal malignancies, rhabdomyosarcoma, lymphoma, etc. can involve cavernous sinuses either by osseous destruction or perineural spread along the cranial nerves. Nasopharyngeal carcinomas are encountered in the 5th and 6th decades of life and have a nonspecific imaging appearance, appearing as heterogeneous masses with heterogeneous post-contrast enhancement and associated osseous destruction (Fig. 8) [14]. Sinonasal malignancies especially primary tumors of the sphenoid sinus can involve cavernous sinuses. Rhabdomyosarcomas are mostly encountered in the pediatric age group and show more homogenous appearance with embryonal subtype whereas alveolar, and pleomorphic subtypes are associated with more heterogeneity and ring pattern of post-contrast enhancement [15]. Lymphomas arising in this region show minimal post-contrast enhancement of mass and may be associated with bulky cervical lymphadenopathy (Fig. 9).

    Fig. 8

    

    Nasopharyngeal carcinoma. Coronal (A) and axial (B) CECT images in a 62-year-old male patient show heterogeneously enhancing mass lesion (white star in A) involving nasopharynx with extension to sphenoid sinus (red star in A) and left cavernous sinus (via osseous erosion of skull base and widening of neural foramina) seen in the form of increased bulk and heterogenous enhancement of the same (red arrow in A and B)

    Fig. 9

    

    Sinonasal lymphoma. Axial (A) and coronal (B) CECT images in a 72-year-old male patient show homogenously enhancing mass lesion involving the right middle cranial fossa and right cavernous sinus which appears bulky (arrows in A and B) along with extension of the mass posteriorly in right prepontine cistern which is seen closely abutting right middle cerebral peduncle (green arrows). There is also widening of right foramen ovale (circle in B) with a soft tissue mass in the right infratemporal fossa (red star in B) suggestive of perineural extension along trigeminal nerve

  • (C) Metastases- Cavernous sinus metastases can occur by hematogenous route or perineural spread with head and neck malignancies being the most common ones to invade cavernous sinuses. Osseous metastases in this region can involve the cavernous sinus. Lung, breast, gastric, and renal primary malignancies may also show distant metastasis to the cavernous sinuses. These have an aggressive imaging appearance usually associated with bone destruction [16].

• (3) Bone tumors of skull base: Any bone tumor near the cavernous sinuses can extend into the same. Those especially having some predilection for this region include chordoma and chondrosarcoma.

  • (A) Chordomas- Chordomas are typical midline tumors arising from primitive notochordal remnant tissues that extend from Rathke’s pouch to the tip of the coccyx. Preferred sites of occurrence include the spheno-occipital region and sacral region [17]. Clival chordomas are seen in the age group of 20–40 years, whereas sacral chordomas predominate occur in the older age group i.e., around 50 years. Chordomas appear as well-defined centrally located tumors showing intermediate to hyperintense signals on T1- and T2-weighted images with heterogenous post-contrast enhancement giving a lobular and fishnet appearance. The intense hyperintense signal on T2-weighted images is attributed to the increased fluid content of physalliferous cells which forms an important constituent of the tumors. Associated irregular areas of bone erosion, destruction, and scattered areas of amorphous, punctate intratumoral calcification are better demonstrated on CT images [18]. Metastases are rarely seen in chordomas. These tumors are locally aggressive, hence at times differentiation from chondrosarcomas becomes difficult based on imaging alone.

  • (B) Chondrosarcomas- Chondrosarcomas, unlike chordomas, are para-midline tumors mostly seen in the older age groups (4th-5th decade). Petro-occipital synchondrosis is the most common site of occurrence and extension of the tumor to the cavernous sinuses is common owing to its invasive nature. These tumors appear markedly hyperintense on T2-weighted images due to the chondroid matrix. The typical ring and arc pattern of calcification is easily demonstrated on CT images, which helps clinch the diagnosis [18, 19](Fig. 10).

    Fig. 10

    

    Chondrosarcoma. Axial (A) and coronal (B) NCCT images along with bone window coronal image (C) in a 54-year-old patient with deranged renal function reveal an osseous heterogeneous expansile mass lesion involving sella, lateral wall of the sphenoid sinus and left anterior clinoid process with multiple areas of punctate ring and arc calcifications (yellow arrow in (C1)). The lateral margin of the mass extends into the left cavernous sinus (star in A and B) and abuts the medial aspect of left temporal lobe (arrow in A and B)

Other tumors/tumor-like conditions and cysts

Other rare lesions affecting cavernous sinuses include hemangioma, histiocytosis, fat-containing or cystic lesions like dermoid and epidermoid cysts, and rarely lipomas. Cavernous sinuses are quite an unusual location for lipoma.

Lipomas in this location may undergo osseous metaplasia to form ossifying lipoma or osteolipoma. These have a classical fat attenuation on CT between -60 and -120 HU and appear bright on T1- and T2-weighted images with signal suppression on fat-saturated sequences (Figure 11). Eccentric foci of calcification may be seen.

Fig. 11

Osteolipoma. Sagittal T1W (A), coronal T2W (B) and axial CISS (C) images in a 30-year-old male patient show a well defined T1 and T2 hyperintense lesion in left cavernous sinus with few hypointense internal septations (yellow arrows in A and B). The signal intensity is similar to subcutaneous fat and shows partial suppression on coronal fat saturated FLAIR image (D) (star in D). Zoomed-in 3D CISS (C1) image through the lesion shows normal neural structures (arrows) in the lateral interdural compartment of left cavernous sinus

Among cystic lesions epidermoid cysts are far more common when compared to dermoid cysts. Imaging appearance is similar to their appearance elsewhere in the brain (Figure 12). Arachnoid cysts are one of the rarest lesions involving cavernous sinuses and show CSF signal intensity on MR imaging sequences. These cystic lesions can have either, extradural or inter-dural locations. Extradural locations are usually associated with bone remodeling/scalloping while a lesion within an inter-dural location tends to displace ICA rather than encasing it [20].

Fig. 12

Epidermoid cyst. Axial T2W (A), coronal FLAIR (B) and post-contrast T1W (C) images in a 7-year-old child reveal a large well defined T2 hyperintense extra-axial mass in right middle cranial fossa involving right cavernous sinus showing only partial suppression on FLAIR and no post-contrast enhancement (red star). The lesion is displacing the right ICA medially (yellow arrow) which shows normal flow void in A with bowing of the right lateral wall of sphenoid sinus alongwith mild extension of the lesion into the posterior fossa

Vascular conditions

The spectrum of vascular pathologies of cavernous sinus includes sinus thrombosis, carotid-cavernous fistulas, aneurysms and dissections involving ICA, etc. Septic thrombosis is one of the most frequently encountered vascular pathologies of the cavernous sinus and can be life-threatening if not managed in time.

Cavernous sinus thrombosis

Bacterial and fungal infections of the paranasal sinuses, orbit, face, and skull base predispose the cavernous sinuses to septic involvement. This occurs due to lack of valves within the tributaries of cavernous sinuses resulting in the bidirectional flow of blood from adjacent areas to the sinuses and vice versa. The most common manifestation is in the form of cavernous sinus thrombosis. Diabetes and immunosuppression are known risk factors for the same. In recent years, cavernous sinus thrombosis has been very frequently seen with invasive fungal infections of mucormycosis in the wake of COVID-19 pandemic. A hyperattenuating thrombus is sometimes seen in the affected sinus on unenhanced CT. Post-contrast scans reveal a bulky cavernous sinus with convex bulge of its lateral wall and filling defects within the sinus (Figure 13). The filling defects need to be differentiated from intrasinus adipose tissue, based on mean attenuation values. In suspected cases of cavernous sinus thrombosis, a delayed scan at about 45-50 seconds post-contrast injection should be performed [6]. MR due to its increased soft tissue and contrast resolution is the imaging modality of choice. On MRI, a bulky sinus with loss of normal flow void of sinus and signal characteristics depending upon the age of the thrombus are seen. Early stages of sinus thrombosis can demonstrate diffusion restriction within the sinus. Other ancillary findings of cavernous sinus thrombosis include engorged and /or thrombosed superior ophthalmic vein, bulky and heterogenous appearing ipsilateral extraocular muscles with surrounding periorbital/ retro-orbital fat stranding [21]. Thrombosis of intracavernous ICA may also be seen. The presence of a markedly T2 hypointense signal in paranasal sinuses which is attributed to the paramagnetic ions (iron and manganese) along with ‘black turbinate’ sign can suggest fungal etiology.

Fig. 13

Cavernous sinus thrombosis in a case of invasive fungal rhinosinusitis. Coronal (A) and axial (B) T2W images show heterogeneous contents in left cavernous sinus(blue arrows)with circumferential thickening of left ICA(green arrows) with mild luminal attenuation. Post-contrast fat-saturated T1W coronal (C, D) images show non enhancing filling defect(yellow arrow) within the sinus with enhancement of left ICA wall (red arrow). There are subacute infarcts involving left temporal lobe and left basal ganglia(yellow stars). In addition, note hypoenhancing left inferior turbinate giving ‘Black turbinate sign’(white arrow) with circumferential mucosal thickening in maxillary sinuses (curved arrows), bilateral ethmoidal air cells and sphenoid sinus. There is heterogeneous enhancement and peripherally enhancing abscess formation in the adjoining masticator space

Carotid-cavernous fistulas

Carotid-cavernous fistulas can be direct/indirect or can be spontaneous/traumatic. In the direct type, there is abnormal communication between the internal carotid artery and cavernous sinuses. In the indirect type, there is abnormal communication between the branches of the internal carotid artery and cavernous sinuses. Usually, the traumatic ones are of the direct type, seen mostly in the young age group and spontaneous ones are of the indirect type, seen mostly in the older age group usually in females. Barrow classified carotid-cavernous fistulas into four types, type A is direct and includes communication between ICA and cavernous sinus. Type B, C, and D are indirect types showing communication between the cavernous sinus and branches of either ICA or ECA. On MR imaging, the involved cavernous sinus appears bulky with prominent flow voids. Other ancillary findings include dilated and tortuous superior ophthalmic vein with increased adjacent flow voids, bulky ipsilateral extraocular muscles along with stranding of the periorbital and retro-orbital fat. Occasionally, a breach in the wall of ICA can also be appreciated with fistulous tract between the dehiscent artery and draining vein giving a snowman appearance. TOF MR angiography can show flow-related enhancement while on post-contrast images early and increased enhancement similar to the artery is seen. The enhancement is usually compared to the ipsilateral transverse sinus [22](Figure 14). Digital subtraction angiography (DSA) which is the gold standard investigation, demonstrates rapid transit of blood from ICA to cavernous sinus along with enlarged draining veins. Time-resolved MR angiography/ dynamic imaging can demonstrate features similar to DSA. Retrograde flow to the ophthalmic veins can also be demonstrated. Apart from diagnosis, DSA can be used for interventional management of this condition.

Fig. 14

Carotid-cavernous fistula-direct type. Axial T2W (A,E) images in a 59-year-old male with post-trauma pulsatile proptosis, show bulky left cavernous sinus with multiple flow voids within and adjacent to the sinus extending to the left orbital apex (arrows in A, E). Axial TOF MR angiography (B, C) images show enlarged left cavernous sinus with convex lateral wall showing asymmetric enhancement with a small defect (red arrow in C) in the wall of left ICA. MIP images (D, F) from the TOF angiography reveal enlarged left cavernous sinus showing flow-related enhancement (star in D and F) along with prominent draining veins

ICA aneurysms

The majority of internal carotid artery aneurysms are detected incidentally in older women (mostly > 50 years). They rupture rarely and manifest with signs and symptoms about the specific location of the aneurysm. Rupture may manifest with subarachnoid hemorrhage, cerebral infarction, and/or epistaxis. On nonenhanced CT they appear as hyperattenuating structures and may or may not show curvilinear mural calcifications. Eccentric thrombus formation within an aneurysmal lumen is not an uncommon finding. Signal intensity on MRI varies with the age of blood products and the patency of/flow rate through the aneurysm. They generally show signal void on T2-weighted images. A hyperintense signal may be attributed to either slow flow/ partial thrombosis [23]. Post-contrast images can be useful in this context (Figure 15). A completely thrombosed aneurysm shows an iso-hyperintense signal on both T1- and T2-weighted images. Sometimes these may be mistaken for a mass lesion but the typical pulsation artifacts seen in phase encoding direction help in clinching the diagnosis. DSA can provide diagnostic confirmation as well as guide the interventional management of these aneurysms.

Fig. 15

ICA aneurysm. Axial T2W (A) and axial MR angiography (TOF) (B) images show an abnormal dilatation of right ICA (when compared to normal left ICA) appearing as flow void on T2W image (arrow in A) and flow-related enhancement on TOF image (red arrow in B). Axial (C) and Coronal (D) post-contrast images show homogenous opacification of the aneurysm involving the cavernous (yellow arrow in C and D) and supra-clinoid segment (green arrow in D) of right ICA

Miscellaneous conditions

Non-infective granulomatous conditions like neurosarcoidosis and non-infective inflammatory conditions involving various facial-orbital structures like orbital pseudotumor may extend intracranially to involve the cavernous sinuses.

Leptomeningeal involvement is the most typical manifestation of neurosarcoidosis, which is seen as diffuse or nodular thickening and enhancement of the leptomeninges on post-contrast T1-weighted images. There is usually a predilection for basilar meninges [24].

Orbital pseudotumor can be idiopathic, Immunoglobulin G4(IgG4) related, associated with other inflammatory and autoimmune conditions like granulomatosis with polyangiitis, systemic lupus erythematosus, polyarteritis nodosa, rheumatoid arthritis, dermatomyositis. Orbital pseudotumors can involve various structures in the orbit. Those presenting as a focal mass or thickening in the orbital apex region may show intracranial extension via superior orbital fissure, optic canal, or inferior orbital fissure. The middle cranial fossa and cavernous sinus are the most common sites of involvement. MRI shows the presence of T1 and often T2 hypointense lesion but can be hyperintense depending upon the stage of disease progression. Contrast enhancement is often variable and depends upon the stage of disease. Early lesions show prominent contrast enhancement owing to inflammatory tissue. As lesions progress, fibrosis develops which typically shows minimal enhancement associated with retraction of adjacent structures (Figure 16). Being a diagnosis of exclusion, the workup of a pseudotumor involves a multidisciplinary approach [25, 26].

Fig. 16

Orbital pseudotumor. Axial T2W (A) and axial post-contrast T1W (B) images of a 37-year-old male patient of systemic lupus erythematosus with complaints of left proptosis reveal marked T2 hypointensity replacing the normal retrobulbar fat in left orbit (red arrows) causing proptosis and showing no significant enhancement on post-contrast images. Extension into the left cavernous sinus is seen (yellow arrow) resulting in narrowing of left ICA (green arrows) better appreciated on MIP MR angiography image (C)

Based on the imaging findings of above described numerous pathologies, an algorithmic approach to cavernous sinus pathologies on CT and MRI has been highlighted in Figures 17 and 18, respectively.

Fig. 17

Approach to cavernous sinus pathologies on CT. (Abbreviations CE: contrast enhancement, NP: nasopharyngeal, SN: sinonasal, JNA: juvenile nasopharyngeal angiofibroma, ICA: internal carotid artery)

Fig. 18

Approach to cavernous sinus pathologies on MRI. (Abbreviations ICA: internal carotid artery, NP: nasopharyngeal, SN: sinonasal) [* Hemangioma shows progressive centripetal enhancement on dynamic contrast-enhanced MRI, # Metastases may present with both bone destruction or sclerosis]

Conclusion

Cavernous sinuses are paired extradural venous sinuses which because of their multiple connections with adjacent nasopharynx, paranasal sinuses and orbital structures form an important gateway to spread of disease to the intracranial compartment which can be disastrous if not diagnosed early. Conditions that involve cavernous sinuses are multifold and include benign and malignant neoplasms, vascular lesions, and infective/inflammatory pathologies. Often, these conditions have overlapping clinical features. It is therefore important that besides routine brain imaging, dedicated thin T1- and T2-weighted axial and coronal images along with delayed contrast-enhanced imaging of cavernous sinus showing enhancement pattern should be performed for diagnosis of cavernous sinus pathologies. When MRI is not available or bone involvement is equivocal on MRI, thin CT in axial and coronal reconstruction with delayed contrast enhancement greatly aids in diagnosis. The radiologists should pay special attention to these small yet important venous structures during imaging else significant pathologies in this region can be easily missed. A multidisciplinary approach with early and effective imaging evaluation can play a critical role in diagnosis and patient management.