Neuroradiology (1997) 39: 811±814  Springer-Verlag 1997

C. J. Chen Y. I. Hsu Y. S. Ho Y. H. Hsu L. J. Wang Y. C. Wong

Received: 31 January 1997 Accepted: 17 February 1997

)

C. J. Chen ( ) ⋅ Y. I. Hsu ⋅ L. J. Wang ⋅ Y. C. Wong Department of Diagnostic Radiology, Chang Gung Memorial Hospital and Medical College, 199 Tung Hwa North Road, Taipei, Taiwan Tel. +8 86-3-3 28 12 00 ext. 37 85; fax +8 86-2-9 21 04 54 Y. S. Ho Department of Pathology, Chang Gung Memorial Hospital and Medical College, Taipei, Taiwan Y. H. Hsu Department of Neurosurgery, Chang Gung Memorial Hospital and Medical College, Taipei, Taiwan

D IA G N O S T I C NE URO R A D IO L OG Y

Intracranial meningeal melanocytoma: CT and MRI

Abstract We report the MRI and CT findings of an intracranial meningeal melanocytoma (IMM) arising from Meckel's cave and review the imaging characteristics of IMM. On CT, IMM constantly appear as well-circumscribed, isodense to slightly dense, extra-axial tumours with homogeneous contrast enhancement. This appearance is nonspecific and similar to that of meningiomas or small neuromas. On MRI, the signal of IMM is strongly related to the amount of melanin pigment: the more melanin, the more shortening of T1 and T2 relaxation times. Only when it shows as a homogeneous mass, bright on T1 and dark on T2 weighting, can a specific diagnosis of a melanin-con-

Introduction Primary intracranial melanocytic tumours are rare. The meningeal melanocytoma is at the benign end of the spectrum of the primary melanotic neoplasms and is less common than its malignant counterparts [1]. This benign tumor has been named pigmented meningioma or melanotic meningioma [2±6], because its characteristics under light microscopy are almost the same as those of meningioma. In 1972, Limas and Tio [7] demonstrated the melanocytic ultrastructure of these tumors by electron microscopy and used the term ªmeningeal melanocytomaº to signify their melanocytic origin. Recently, immunohistochemical study with antimelanoma antibody (HMB-45) and epithelial membrane antigen also helps to confirm the melanocytic origin [8, 9]. Less than 20 cases of intracranial

taining tumour be made. However, this still cannot provide a distinction between IMM and malignant meningeal melanoma. Key words Meningeal melanocytoma ⋅ Magnetic resonance imaging ⋅ Computed tomography

meningeal melanocytoma (IMM) have been reported in the English-language literature [2±6, 9±17]; only 4 had detailed magnetic resonance (MR) descriptions [13±15]. We report an IMM arising from Meckel's cave, with CT and MRI studies. The imaging characteristics are reviewed and the differential diagnosis discussed.

Case report A 41-year-old woman had had numbness of the right side of her face for 1 year, increasing over the preceding 2 months. Examinations revealed only decreased pin-pick sensation over the distribution of the right trigeminal nerve, with muscle atrophy. CT revealed a 2.5-cm-diameter, slightly dense tumour arising from the right Meckel's cave, with adjacent bony erosion (Fig. 1 a), which showed strong, homogeneous contrast enhancement (Fig. 1 b).

812

Fig. 1 a CT shows a slightly dense tumour (arrow) at the right Meckel's cave with adjacent bony erosion. b This shows homogeneous contrast enhancement (arrow). A small portion of the tumour protrudes into the pontine cistern Fig. 2 a T1-weighted image (TR/TE 466/19) shows an extra-axial, homogeneously highsignal tumour (arrow). b A T2weighted image (3,166/91.3) indicates marked T2 shortening (arrow).

1a

b

2a

b

MRI at 1.5 T showed the mass to give homogeneously high signal on T1-weighted images (TR/TE 466/19) and low signal on T2-weighted images (3,166/91.3) (Fig. 2). Because the tumour was so bright on unenhanced T1-weighted images, it was very difficult to perceive any contrast enhancement. At operation a hard, fibrous tumour arising from the right Meckel's cave was totally excised. The specimen showed no evidence of bleeding grossly or microscopically. On light microscopy, the tumour was composed of spindle and epithelioid cells with well-defined cytoplasm, and prominent nucleoli. Cell whorls were frequent and no anaplastic features were observed. There were numerous cytoplasmic pigment deposits consistent with melanin (Fig. 3). Immunohistochemical study was positive with HMB-45 and negative with epithelial membrane antigen, indicating the melanocytic origin of the tumour. The diagnosis of meningeal melanocytoma was thus made. Follow-up MRI 1 year later showed no evidence of tumour recurrence.

Discussion Meningeal melanocytomas are benign tumours arising from the melanocytes occurring in normal leptomeninges. These leptomeningeal melanocytes are derived

from the neural crest during early embryonic development and are found mainly in the posterior cranial fossa [18]. Most reported IMM are thus in the posterior cranial fossa, especially ventral to the brain stem or posteriorly adjacent to the foramen magnum [2, 3, 5, 6, 9, 12± 15]. Meckel's cave is the second most common location [4, 10, 11, 16, 17]. Most of the patients have been female, aged between 9 and 71 years (mean 44 years). The duration of symptoms before diagnosis was from several weeks to 14 years, with 70 % of patients having symptoms for more than 8 months (Table 1). On CT [10±16], IMM constantly appear as well-circumscribed, isodense to slightly dense, extra-axial tumours with homogeneous enhancement, similar to meningiomas. Tumour calcification and hyperostosis of adjacent bone have rarely been described in IMM; nevertheless, lack of these signs obviously does not exclude a meningioma [19, 20]. Another differential diagnosis is neuroma, especially a small one. Small neuromas usually show uniform contrast enhancement, whereas larger neuromas may be heterogeneous [21]. Only five reports of IMM, including ours, have descriptions of the MRI signal changes with different pulse

813

Fig. 3 A photomicrograph of the tumour shows clusters of epithelioid cells with well-defined cytoplasm and numerous cytoplasmic melanin pigment deposits. (Haematoxylin and eosin, original magnification × 233)

Table 1 Reported cases of intracranial meningeal melanocytoma. F female, M male, T1WI, T2WI T1-, T2-weighted images Reference

Sex/age (years)

Duration of symptoms

Location

[2]

F/45

1 year

Cisterna magna

[3] [4]

M/51 F/35

6 years 2 years

Anterior to pons Meckel's cave

[5]

F/44

4 months

Adjacent to pons and cerebellum

[10]

F/43

10 years

Meckel's cave

[6] [11]

F/52 M/9

8 months 3 months

Vermis Meckel's cave

[12]

F/27

1 year 10 months

Tentorium/vermis

[14] [15]

F/68 M/62

6 weeks 1 year

Foramen magnum Foramen magnum

[16]

F/27

8 years

Meckel's cave

[13]

F/67 M/32

14 years 2 years

[9]

F/40

several weeks

F/71

3 months

Cerebellopontine angle Anterior to pons and medulla Temporal lobe convexity and cerebellum Tentorial notch

F/49

8 years

Foramen magnum

F/30 F/41

? 1 year

Cavernous sinus Meckel's cave

[17] Present case

sequences. The IMM reported by Litofsky et al. [13] was homogeneously isointense on T1-weighted images and gave high signal on T2-weighted images throughout most of the tumour, i. e., it was similar to the most intracranial tumours. The pathological specimen showed

Signal intensity on MRI

Homogeneous isointensity on T1WI, low on T2WI Homogeneous high signal on T1WI, low on T2WI

Mainly homogeneous isointensity on T1WI, high on T2WI; A small part high on T1WI and T2WI, due to haemorrhage

Homogeneous isointensity on T1WI, low on T2WI Homogeneous high signal on T1WI, low on T2WI

little melanin pigment. The cases of Naul et al. [14] and Faro et al. [17] were homogeneously isointense on T1weighted images but gave low signal on T2-weighted images. The latter was attributed to either fibrous content of the neoplasm or the paramagnetic effect of the

814

melanin; however, why the T1 signal change was different from that usually seen in melanin-containing tumours was not explained. Nevertheless, on microscopic examination, the tumour cells contained scattered areas of cytoplasmic pigment deposition. The IMM reported by Uematsu et al. [15] and by us gave homogeneously high signal on T1-weighted and low signal on T2weighted images. The pathological specimens showed numerous brown granules consistent with melanin. It thus seems that the signal of IMM is strongly related to the amount of melanin present: the more melanin, the more shortening of the T1 and T2 relaxation times. Gomori et al. [22], correlating the melanin content of six choroidal melanomas with their MRI appearances, also found this trend toward shorter T1 and T2 relaxation times with increasing melanin content. They suggested that these signal changes resulted from the paramag-

netic stable free radicals, such as indole semiquinones and semiquinonimines, in melanin [22]. Although Woodruff et al. [23] stressed that haemorrhage in malignant melanoma may have a greater influence on the appearances than melanin, absence of haemorrhage in most pathological specimen strongly supports the important role of melanin in influencing the signal changes. Since the biological behaviour and treatment of relatively benign meningeal melanocytoma and the more aggressive meningeal melanoma are different, the importance of making the correct diagnosis is obvious. Unfortunately, it seems that imaging studies, including MRI, cannot provide this service [17]. Features, we thought helpful in this case were the duration of symptoms of more than 8 months and the typical location in the posterior cranial fossa or Meckel's cave.

References 1. Russell DS, Rubinstein LN (1989) Pathology of tumors of the nervous system. Williams & Wilkins, Baltimore, pp 794±797 2. Ray BS, Foot NC (1940) Primary melanotic tumors of the meninges: resemblance to meningiomas. Report of two cases in which operation was performed. Arch Neurol Psychiat 44: 104±177 3. Keegan HR, Mullan S (1962) Pigmented meningiomas: an unusual variant. Report of a case with review of the literature. J Neurosurg 19: 696±698 4. Turnbull IM, Tom MI (1963) Pigmented meningioma. J Neurosurg 20: 76±80 È ber 5. Tzonos T, Brunngraber CV (1963) U das melanoblastische Meningiom. Acta Neurochir (Wien) 11: 416±421 6. Portugal JR, Alencar A, Brito Lira LC, Carvalho P (1984) Melanotic meningioma complicated by disseminated intravascular coagulation. Surg Neurol 21: 275±281 7. Limas C, Tio FO (1972) Meningeal melanocytoma (ªmelanotic meningiomaº). Its melanocytic origin revealed by electron microscopy. Cancer 30: 1286± 1294 8. OrdoÂnÄez NG, Sneige N, Hickey RC, Brooks TE (1988) Use of monoclonal antibody HMB-45 in the cytologic diagnosis of melanoma. Acta Cytol 32: 684±688

9. O'Brien TF, Moran M, Miller JH, Hensley SD (1995) Meningeal melanocytoma. An uncommon diagnostic pitfall in surgical neuropathology. Arch Pathol Lab Med 119: 542±546 10. Botticelli AR, Villani M, Angiari P, Peserico L (1983) Meningeal melanocytoma of Meckel's cave associated with ispilateral Ota's nevus. Case report. Cancer 51: 2304±2310 11. Winston KR, Sotrel A, Schnitt SJ (1987) Meningeal melanocytoma. Case report and review of the clinical and histological features. J Neurosurg 66: 50±57 12. Jellinger K, BoÈck F, Brenner H (1988) Meningeal melanocytoma. Report of a case and review of the literature. Acta Neurochir (Wien) 94: 78±87 13. Litofsky NS, Zee CS, Breeze RE, Chandrasoma PT (1992) Meningeal melanocytoma: diagnostic criteria for a rare lesion. Neurosurgery 31: 945±948 14. Naul LG, Hise JH, Bauserman SC, Todd FD (1991) CT and MR of meningeal melanocytoma. AJNR 12: 315±316 15. Uematsu Y, Yukawa S, Yokote H, Itakura T, Hayashi S, Komai N (1992) Meningeal melanocytoma: magnetic resonance imaging characteristics and pathological features. J Neurosurg 76: 705±709 16. Prabhu SS, Lynch PG, Keogh AJ, Parekh HC (1993) Intracranial meningeal melanocytoma: a report of two cases and a review of the literature. Surg Neurol 40: 516±521

17. Faro SH, Koenigsbery RA, Turtz AR, Croul SE (1996) Melanocytoma of the cavernous sinus: CT and MR findings. AJNR 17: 1087±1090 18. Goldgeier MH, Klein LE, Klein-Angerer S, Moellmann G, Nordlund JJ (1984) The distribution of melanocytes in the leptomeninges of the human brain. J Invest Dermatol 82: 235±238 19. Claveria LE, Sutton D, Tress BM (1977) The radiological diagnosis of meningiomas, the impact of EMI scanning. Br J Radiol 50: 15±22 20. Rohringer M, Sutherland GR, Louw DF, Sima AAF (1989) Incidence and clinicopathological features of meningioma. J Neurosurg 71: 665±672 21. Cohen LM, Schwartz AM, Rockoff SD (1986) Benign schwannoma: pathologic basis for CT inhomogeneities. AJR 147: 141±143 22. Gomori JM, Grossman RI, Shields JA, Augsburger JJ, Joseph PM, DeSimeone D (1986) Choroidal melanomas: correlation of NMR spectroscopy and MR imaging. Radiology 158: 443±445 23. Woodruff WW Jr, Djang WT, McLendon RE, Heinz ER, Voorhees DR (1987) Intracerebral malignant melanoma: high-field-strength MR imaging. Radiology 165: 209±213