Neuroradiologg

Neuroradiology (1982) 23:133-139

© Springer-Verlag 1982

Mucoceles in the Paranasal Sinuses Involving the Orbit: CT Signs in 43 Cases S. Perugini 1, U. Pasquini 1, F. Menichelli 1, U. Salvolini, M. de Nicola 1, C. M. Valazzi 2, S. Benedetti 2 and R. Tittarelli 2 1Neuroradiology Service, Ospedale Civile "Umberto I", zOphthalmic Clinic, University of Ancona, Ancona, Italy

Summary. The diagnostic value of computed tomography was verified in the study of mucoceles in the paranasal sinuses involving the orbit. The CT data on 43 patients with clinical suspicion of mucocele highlight the characteristic signs; 26 were found to have a mucocele at operation.

Key words: Mucoceles - CT - Orbit - Paranasal sinuses

to have a mucocele. In the others the clinical diagnosis was considered to be final and surgery was held to be unnecessary. CT scanning was done with an EMI Mark 1 scanner using overlapping 8-ram cuts on a plane parallel to the neuro-ocular plane [23]. The scans were done before and after IV infusion of contrast medium, 2 cc/kg body weight at a concentration of 30% I.

Results

Introduction The possibilities of computed tomography (CT) in ophthalmic [1-6] and ear, nose and throat diseases [7-15] were immediately recognised after its introduction in 1974. In 1978 papers dealing more particularly with the CT study of mucoceles (16-22] began to appear. This study is based on over 5 years' experience with skull and brain CT in about 1000 cases of orbital and sinus disease. Our purpose is to assess the diagnostic value of CT in mucoceles in the paranasal sinuses involving the orbit.

Patients and Methods A total of 43 patients (26 men and 17 women) with clinical suspicion of mucocele were examined and 5 of them were followed up after surgery; their ages are given in Table 1. Of these patients, 41 had orbital involvement, and only 1 case had concomitant intracranial invasion. The paranasal sinuses most frequently affected in our series were the frontal sinuses and the anterior ethmoidal cells or both (see Table 1); we had no mucoceles of the maxillary sinuses. Of the 43 patients, 26 were operated on and were found

Analysis of the case series (Table 2), with special reference to the 26 cases verified surgically, enabled us to identify some constant CT signs of high specificity

Table 1. (see text)

Frontal M. Frontoethmoid M. Ethmoidal M. Ethmoidal M. (bilateral) Maxillary M. Sphenoid M. Compound M.

No. Mucocele

With orbital Without orbiinvolvement tal involvement

14 12 12

12 12 12

2 = 2 1

2 = 2 1

2

Table 2. (see text) CT No. Mucocele Typical Verified surgically 26 Not verified surgically 17 Total

43

Atypical

Negative

19

6

1

15

2

=

34

8

1

0028-3940/82/0023/0133/$01.40

134 Table 3. (see text) Authors

No. Cases

Som PM et al. [21]

-

Villant R et al. [22] Price HI et al. [19] Hesselink JR et al. [17] Osborn A G et al. [18] Personal cases

4

Verified

4

1

2

3

4

5

Exceptions

+

+

+

_

_

bilateral ethmoidal m. septa not destroyed

+

+

+

-

+

perifocal thickening of the bone structures

7

1

+

+

+

-

+

18

18

+

+

+

-+

+

2

2

+

+

/

/

+

43

26

+

+

+

+

+

Fig.1. Right fronto-ethmoid mucocele. Clear-cut bone destruction. At the edges of the bone defect is a bony spur, which follows the outer walls the mucocele; it is probably a partial ossification of the stripped periosteum (21680)

hyperdense rim (mucopyoceles)

Fig. 2. Right fronto-ethmoido-orbital mucocele. The intrinsic density is homogeneous. Partial ossification of the mucocele wall and hyperdense rim in the uncalcified zones (10173)

if they are simultaneously present (without enhancement): (Table 3) 1. Mass of the same density as the cerebral parenchyma occupying the sinus structure, often with exophytic development 2. Clear-cut margins of the lesion on the orbital and intracranial sides without signs of infiltration of adjacent anatomical structures 3. Osteolysis of the sinus structures with regular but thickened margins.

Fig.3. Left fronto-orbital mucocele. The axial scans do not show the relationships between the process occupying the orbit and the lateral extension of the frontal sinus. Hyperdense rim and content of homogeneous density equal to that of brain tissue (12734)

(After enhancement): 4. Hyperdense and regular rim on the orbital and intracranial side (capsule type) 5. No variations in the density of the intrinsic tissue All these signs were present and associated in 19 of 26 cases, which were verified surgically and are therefore called typical. A partial shell-like calcification of the wall on the orbital side was observed in 5 of these patients. A thickening of the bone structures

Fig.4. Left ethmoido-orbital mococele. Mass of homogeneous intrinsic density. Hyperdense rim on the orbital side. Note the perfect definition of the homolateral m. rectus medialis stripped from the lamina papyracea and not infiltrated (13 963)

135

Fig. 6. Left fronto-ethmoid mucocele with large intracranial extension. The scan shows the destruction of the posterior wall of the frontal sinus with intracranial extension of the mucocele as a formation of homogeneous density equal to that of brain tissue and thickened hyperdense wall after contrast infusion. This wall probably corresponds to the capsule of the mucocele and to the meninges that separate the mucocele from the brain mass (8975)

Fig.5. Left fronto-ethmoido-orbital mucocele. Mass of homogeneous intrinsic density with hyperdense rim on the orbital side. Note the erosion of the anterior and posterior wall of the affected frontal sinus. The scan at this level after contrast infusion clearly shows the limits of the lesion on the encephalic side and highlights the sharp separation from the brain structures (10043)

adjacent to the walls of the sinus was present in the two cases of sphenoidal mucocele. The remaining 7 of the 26 surgically verified cases were atypical and deserve a detailed examination. Four mucoceles showed bone erosion with ill-defined margins: the irregularity of the bone finding

may be explained by a previous operation on the paranasal sinuses in two cases and by a former facial injury in the other two; two mucoceles presented unevenly increased intrinsic density: at the time of the investigation the patients were suffering from acute orbital inflammation and at operation a mucopyocele was found: one patient who was negative on CT proved at operation to have a small mucocele deriving from the ethmoidal cells. As many as 15 of the 17 cases not undergoing surgery had the features described above as typical of mucocele. Discussion

When comparing our results with those reported in the literature (Table 3), we find that all authors agree about the homogeneity of the mucocele mass and the isodensity relative to brain tissue found in this disease [27-22]. Hesselink et al. [17] found this in 12 cases of 18. The published data also confirm our

136

Fig. 7. Bilateral ethmoid mucocele. At the level of the ethmoid region is a tissue of homogeneous intrinsic density. Bone erosion is not complete, for the intrasinusal bony septa remain. After contrast infusion there are no variations in intrinsic density but a hyperdense rim on the orbital side (7987)

Fig. 9 a and b. Sphenoid mucocele, a) Extension of the sphenoid sinus anteriorly to the right towards the orbit and sellar region with destruction of its walls. At the periphery of the zones of bone destruction a hyperdense rim is present after contrast infusion. The content is homogeneous and isodense relative to brain tissue (4025). b) Postoperative pattern: there is air in the cavities of the mucocele (5559)

Fig.8. Post-tramatic bilateral fronto-ethmoido-orbital mucocele. Atypical pattern: numerous sacs of homogeneous density are separated by bony septa. The intrinsic density is nonetheless homogeneous and does not vary after contrast infusion. The extension of the lesion, which occupies a large part of the facial bone complex, is not unusual (5852)

Fig.10. Hypophyseal adenoma with development into the sphenoid sinus. Space-occupying process of uneven intrinsic density, becoming irregularly hyperdense after contrast infusion in the sella turcica and sphenoid sinus; in this case the characteristic hyperdense rim is missing (differential diagnosis from the sphenoid mucocele of Fig.9) (11618)

Fig. 11. Right ethmoid mucopyocele. The limits of bone erosion are clear. After contrast infusion the intrinsic density of the ethmoido-orbital lesion increases and an irregular hyperdense rim appears. Concomitant alteration of the extraconal tissue at the apex of the orbit, which appears irregularly hyperdense after contrast infusion (19105)

137

findings with regard to associated sinus bone changes; only in the two cases of bilateral ethmoidal mucocele were the intrasinusal bony septa not completely destroyed, as Som et al. [21] found. All works agree that there is no increase in the intrinsic density of the mucoceles after infusion of contrast medium. The hyperdense rim we observed in all the mucoceles verified surgically were found in only 2 of the 18 cases mentioned by Hesselink et al. [17]. However, it should be noted that our contrast-enhancement method involves high quantities of iodised contrast, whereas this was not stated by other workers. It is therefore probable that the hyperdense rim is due to impregnation of the periosteum with contrast medium, as happens with the dura mater at brain level. This supposition is confirmed by the usual continui-

ty of the mucocele walls with what remains of the walls of the affected sinus. In the zone of greatest erosion the sac of the mucocele is contained only by the periosteum, the last structure to demarcate it once the bone has been resorbed. On the other hand, we often found calcifications of the wall in the zone adjoining the orbit, where the bone was undergoing destruction, and ossification of the margins of osteolysis with the formation of bony spurs in the direction of development of the walls of the mucocele sac. This may be a reaction on the part of the periosteum. However, this latter feature is quite nonspecific, since it is also found in slow-growing, benign, spaceoccupying lesions originating in the sinuses.

Differential Diagnosis

Fig. 12. Lymphoma of the left maxillary and ethmoid paranasal sinuses. Intrinsically homogeneous mass with fairly definite limits on the orbital side. However, the characteristic rim does not appear after contrast infusion, but there is an irregular increase in intrinsic density (15542) differential diagnosis from the mucopyocele of Fig. 11)

In our clinical experience we have sometimes encountered lesions simulating a mucocele, so we are citing a few examples for the purpose of correct differential diagnosis. As a rule, they are benign, spaceoccupying lesions of the paranasal sinuses and orbit. Schwannoma may have all the features of mucopyocele in that after contrast infusion it becomes slightly, but unevenly hyperdense. Chondroma may look like a mass of intrinsic density similar to that of the brain, with hyperdense rim after contrast enhancement both on the orbital and intracranial sides with marked intrinsic structure. Ethmoidal chondromyxoma shows a more definite irregularity both of the walls and of the included septa: it must be differentiated from bilateral ethmoidal mucocele. Before enhancement, lymphoma of the paranasal sinuses with concomitant orbital involvement may have a pattern very similar to that of a mucocele; after enhancement, however, it does not present the characteristic

Fig. 13. Left ethmoid mucopyocele. Sac of slightly uneven density after contrast infusion. Partly calcified shell present on the orbital side. Concomitant lack of homogeneity of the retrobulbar fat and increased volume of the m. rectus medialis (inflammatory pseudotumour) (20487)

Fig. 14. Ethmoid schwannoma. Uneven intrinsic density after contrast infusion and partially calcified shell on the orbital side. The orbitalstructures are no longer inflamed (differential diagnosis from the mucopyocele of Fig. 13)

138

specific for diagnosis of mucocele appear simultaneously, with the exception of some cases of partially cystic hypophyseal adenoma.

Conclusion Fig. 15. Ethmoid chondroma. Extensive bone destruction of the ethmoid region, where there is a finely structured mass isodense relative to brain tissue with irregular hyperdense septa after contrast infusion (21574)

Our experience indicates that in the majority of cases CT can supply a reliable diagnosis of mucocele of the paranasal sinuses with orbital development, except in complicated mucocele (sequels of surgery, post-traumatic cases, mucopyoceles and so forth). Plain X-rays and tomography rarely offer further guidance. There are no other radiological investigations at the moment that can contribute anything further to tissue diagnosis except ultrasound, especially using the B-mode coupled with the calibrated Amode. Even so, only CT is capable of showing any intracranial complications. Further developments of the method and equipment are likely to supply still more evidence helpful for accurate diagnosis.

References

Fig. 16. Ethmoid chondromyxoma. Pattern very similar to that of chondroma (see Fig.15). Marked irregularity of the bony walls. Presence of intralesional septa. The orbital structures, clearly evident, are displaced (8375)

rim, but an irregular increase in overall density. A partially cystic hypophyseal adenoma with sphenoidal development may show all the CT characteristics of mucoceles of the region. Characteristics very similar to those of mucoceles may be found in retrobulbar cysts, the only definite distinguishing features being a lower intrinsic density relative to the brain and marked involvement of the paranasal sinuses. We would like to point out nonetheless that in none of the diseases listed above do all five signs given as

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