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(Radiographics. 2001;21:625-639.)
© RSNA, 2001

Education Exhibit

A Variety of Appearances of Malignant Melanoma in the Head: A Review1

Edward J. Escott, MD

1 From the Section of Neuroradiology, Department of Radiology, University of Colorado Health Sciences Center, Denver. Received May 4, 2000; revision requested June 12 and received August 4; accepted August 7. Address correspondence to the author, Desert Medical Imaging, 74-785 Highway 111, Suite 101, Indian Wells, CA 92210 (e-mail: edescott@yahoo.com).


   Abstract
Top
 Abstract
LEARNING OBJECTIVES
 Introduction
 Usual Appearances
 Other Appearances
 Locations
 Conclusions
 References
 
Imaging is frequently requested to evaluate patients with malignant melanoma for metastases. When melanoma metastasizes to the head, the lesions can have a variety of appearances and can occur in a variety of locations. The usual appearances of malignant melanoma on magnetic resonance images include the melanotic and amelanotic patterns. The melanotic pattern consists of high signal intensity on T1-weighted images and low signal intensity on T2-weighted images. In the amelanotic pattern, the lesion is hypointense or isointense to the cortex on T1-weighted images and hyperintense or isointense to the cortex on T2-weighted images. However, there is frequent deviation from these patterns. Other patterns include small and rapidly growing metastases, miliary metastases, and subependymal metastases. Although the brain is the most common site of metastases to the head from melanoma, melanoma can metastasize to almost any intracranial or extracranial structure. Structures in the head that can be involved by metastases from melanoma include bone, muscle, the nasopharynx and mucosa, the parotid gland, the meninges, the choroid plexus, the internal auditory canal, and the orbit. The radiologist needs to be aware of these varied appearances and the relatively ubiquitous sites of involvement to better detect these lesions.

Index Terms: Brain neoplasms, secondary, 10.389 • Head and neck neoplasms, diagnosis, 10.33, 10.389, 20.375 • Melanoma, 10.121411, 10.33, 10.389, 20.121411, 20.375 • Skull, secondary neoplasms, 10.33


   LEARNING OBJECTIVES
Top
 Abstract
 LEARNING OBJECTIVES
Introduction
 Usual Appearances
 Other Appearances
 Locations
 Conclusions
 References
 
After reading this article and taking the test, the reader will be able to:


   Introduction
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
Usual Appearances
 Other Appearances
 Locations
 Conclusions
 References
 
Metastatic malignant melanoma is a commonly encountered neoplasm in the head, both intracranially and extracranially. Many prior articles have concentrated on the signal intensity characteristics of melanoma metastases, and there are also case reports describing unusual appearances or locations of such metastases; however, to my knowledge, there is no compendium of the large spectrum of appearances (1–4). The radiologist needs to be aware of the appearances and relatively ubiquitous sites of metastatic melanoma to better detect these lesions.

This article discusses and illustrates the usual appearances, other appearances, and locations of malignant melanoma in the head, as well as its signal intensity characteristics on magnetic resonance (MR) images. Images that demonstrate the wide range of appearances and locations of melanoma metastases to both the intracranial and extracranial structures of the head were selected from the screening and follow-up images of patients who underwent treatment for malignant melanoma at the University of Colorado Health Sciences Center between 1995 and 1999.


   Usual Appearances
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Usual Appearances
Other Appearances
 Locations
 Conclusions
 References
 
Melanotic Pattern
A typical appearance of melanoma has been described by many authors (1,2). This appearance consists of high signal intensity on T1-weighted images and low signal intensity on T2-weighted images (Fig 1). Woodruff et al (2) found that this was the dominant pattern in their study, being present in nine of 19 lesions (47%). They attribute this appearance to the effects of both free radicals in melanin as well as blood products. They suggest that the products of hemorrhage may have a greater influence than the melanin components, since one of the four lesions that had the typical pattern and that were surgically resected showed no microscopic evidence of melanin at lesion analysis. However, one lesion that was resected and that was isointense on T2-weighted images contained no blood products; therefore, the T2 shortening was presumed to be due to the effects of melanin.



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  		Figure 1a.   Melanotic pattern of melanoma in a 54-year-old man who developed brain metastases almost 9 years after resection of an acral lentiginous melanoma of the distal thumb. (a) Nonenhanced axial T1-weighted MR image (repetition time msec/echo time msec = 800/16, one signal acquired) shows two peripherally located nodules (arrows), both of which are hyperintense. There was probable mild enhancement after administration of contrast material. (b) Axial T2-weighted MR image (4,500/95, one signal acquired) obtained at the same level shows the nodules to be hypointense (arrows) with mild surrounding reaction (arrowheads).

 


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  		Figure 1b.   Melanotic pattern of melanoma in a 54-year-old man who developed brain metastases almost 9 years after resection of an acral lentiginous melanoma of the distal thumb. (a) Nonenhanced axial T1-weighted MR image (repetition time msec/echo time msec = 800/16, one signal acquired) shows two peripherally located nodules (arrows), both of which are hyperintense. There was probable mild enhancement after administration of contrast material. (b) Axial T2-weighted MR image (4,500/95, one signal acquired) obtained at the same level shows the nodules to be hypointense (arrows) with mild surrounding reaction (arrowheads).

 
Isiklar et al (1) correlated the MR imaging appearances of 42 lesions with their percentages of melanin-containing cells after resection. They found that a minority (10 of 42 [24%]) had the typical pattern. All of these lesions contained melanin, and seven of the 10 had more than 10% melanin-containing cells. They also found that the greater the concentration of melanin, the greater the high signal intensity on T1-weighted images and the greater the low signal intensity on T2-weighted images. Although they mention that blood products could result in these appearances, they do not believe that blood products were the dominant influence on signal intensity in all cases.

Marx et al (3) evaluated the appearances of 25 cases of melanoma in multiple sites in the body and found that seven of 13 ocular melanomas (54%) had the typical appearance but that only one extraocular lesion did (a brain metastasis with both hemorrhagic and nonhemorrhagic foci). They postulate that the reasons for this finding were differing concentrations of melanin, the effect of blood products, the wide range of repetition times and echo times used in the sequences, and the apparent brightness or darkness of a lesion in relation to the signal intensity of the tissues surrounding it.

Amelanotic Pattern
The other commonly described pattern is the amelanotic pattern. In this pattern, the lesion is hypointense or isointense to the cortex on T1-weighted images and hyperintense or isointense to the cortex on T2-weighted images (Fig 2). In the study of Isiklar et al (1), among lesions that were amelanotic at histologic analysis, six demonstrated the amelanotic imaging pattern, with one appearing like a hematoma, and the remainder had variable signal intensities. Over half of the tumors (10 of 16) that demonstrated the imaging characteristics of amelanotic melanoma contained melanin, although nine of the 10 had less than 10% melanin-containing cells. Overall, 16 of the 42 lesions in their series (38%) demonstrated the amelanotic pattern.



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  		Figure 2a.   Amelanotic pattern of melanoma in a 40-year-old man with brain metastases. (a) Nonenhanced axial T1-weighted MR image (450/11, two signals acquired) shows a lesion that is mildly hypointense (arrow) and lesions that are only faintly seen (arrowheads). (b) Contrast material-enhanced axial T1-weighted MR image (650/11, two signals acquired) shows that the lesions enhance, although there are nonenhancing and less enhancing areas as well in the larger lesion (arrow), which are possibly related to areas of necrosis. (c) Axial T2-weighted MR image (4,000/96, two signals acquired) shows that the largest lesion is heterogeneous (arrow), with areas of high signal intensity as well as areas that are isointense to the brain. The patient’s two largest lesions, including the right parietal one shown in a-c, were resected, and they were amelanotic at histopathologic evaluation.

 


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  		Figure 2b.   Amelanotic pattern of melanoma in a 40-year-old man with brain metastases. (a) Nonenhanced axial T1-weighted MR image (450/11, two signals acquired) shows a lesion that is mildly hypointense (arrow) and lesions that are only faintly seen (arrowheads). (b) Contrast material-enhanced axial T1-weighted MR image (650/11, two signals acquired) shows that the lesions enhance, although there are nonenhancing and less enhancing areas as well in the larger lesion (arrow), which are possibly related to areas of necrosis. (c) Axial T2-weighted MR image (4,000/96, two signals acquired) shows that the largest lesion is heterogeneous (arrow), with areas of high signal intensity as well as areas that are isointense to the brain. The patient’s two largest lesions, including the right parietal one shown in a-c, were resected, and they were amelanotic at histopathologic evaluation.

 


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  		Figure 2c.   Amelanotic pattern of melanoma in a 40-year-old man with brain metastases. (a) Nonenhanced axial T1-weighted MR image (450/11, two signals acquired) shows a lesion that is mildly hypointense (arrow) and lesions that are only faintly seen (arrowheads). (b) Contrast material-enhanced axial T1-weighted MR image (650/11, two signals acquired) shows that the lesions enhance, although there are nonenhancing and less enhancing areas as well in the larger lesion (arrow), which are possibly related to areas of necrosis. (c) Axial T2-weighted MR image (4,000/96, two signals acquired) shows that the largest lesion is heterogeneous (arrow), with areas of high signal intensity as well as areas that are isointense to the brain. The patient’s two largest lesions, including the right parietal one shown in a-c, were resected, and they were amelanotic at histopathologic evaluation.

 
Other Patterns
Melanoma can also have appearances different from the melanotic or amelanotic pattern, as well as have signal intensity that is related to an associated hematoma. Arriaga et al (5), in a study of four lesions in the cerebellopontine angles and internal auditory canals in three patients, found that the lesions did not have the typical signal intensity of melanoma but were isointense on T1-weighted images and hyperintense on T2-weighted images. Hammersmith et al (6), in a study of five cases of nasopharyngeal and paranasal sinus melanoma, found that there were extremely variable amounts of paramagnetic substances in the lesions, including both melanin and products of hemorrhage. The dominant portions of four of the tumors were hypointense on T1-weighted images and hyperintense on T2-weighted images. These authors state that the T1 shortening more often appeared to be a reflection of the paramagnetic effects associated with the products of hemorrhage rather than the presence of melanin.

On the basis of the results of these studies, there is no clear consensus as to whether the appearance of melanoma is due primarily to the paramagnetic effects of blood products or of melanin, and it is likely due to variable contributions from both (1–3,6).


   Other Appearances
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Usual Appearances
 Other Appearances
Locations
 Conclusions
 References
 
Small, Rapidly Growing
Melanoma metastases can be extremely subtle and small, and they can be obscured by artifact or mistaken for normal vessels (Figs 3, 4). They can also grow rapidly, and therefore close follow-up studies can be very helpful.



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  		Figure 3a.   Small, rapidly growing metastases in a 49-year-old man with multiple pigmented lesions all over his body. A melanoma was resected from his upper back 1 year earlier (April 16, 1997). (a, b) Contrast-enhanced axial T1-weighted MR image of the inferior temporal lobes (a) and coronal T1-weighted MR image of the posterior occipital lobes (b) (750/20, one signal acquired) (both obtained March 4, 1998) show two subtle lesions. Tiny areas of possible enhancement are seen but were thought to represent artifact or vessels. The tiny hyperintense focus in the right temporal lobe (arrow in a) is within an area of artifact and was thought to be artifactual or related to a vessel. The hyperintense focus in the left occipital lobe (arrow in b) was seen only on coronal images and therefore was of only low suspicion and was thought to probably represent a vessel. (c, d) Contrast-enhanced axial T1-weighted MR image (similar level and same parameters as in a) (c) and coronal T1-weighted MR image (same level and parameters as in b) (d) (both obtained April 22, 1998) show definite lesions (arrow), which appear as small enhancing nodules.

 


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  		Figure 3b.   Small, rapidly growing metastases in a 49-year-old man with multiple pigmented lesions all over his body. A melanoma was resected from his upper back 1 year earlier (April 16, 1997). (a, b) Contrast-enhanced axial T1-weighted MR image of the inferior temporal lobes (a) and coronal T1-weighted MR image of the posterior occipital lobes (b) (750/20, one signal acquired) (both obtained March 4, 1998) show two subtle lesions. Tiny areas of possible enhancement are seen but were thought to represent artifact or vessels. The tiny hyperintense focus in the right temporal lobe (arrow in a) is within an area of artifact and was thought to be artifactual or related to a vessel. The hyperintense focus in the left occipital lobe (arrow in b) was seen only on coronal images and therefore was of only low suspicion and was thought to probably represent a vessel. (c, d) Contrast-enhanced axial T1-weighted MR image (similar level and same parameters as in a) (c) and coronal T1-weighted MR image (same level and parameters as in b) (d) (both obtained April 22, 1998) show definite lesions (arrow), which appear as small enhancing nodules.

 


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  		Figure 3c.   Small, rapidly growing metastases in a 49-year-old man with multiple pigmented lesions all over his body. A melanoma was resected from his upper back 1 year earlier (April 16, 1997). (a, b) Contrast-enhanced axial T1-weighted MR image of the inferior temporal lobes (a) and coronal T1-weighted MR image of the posterior occipital lobes (b) (750/20, one signal acquired) (both obtained March 4, 1998) show two subtle lesions. Tiny areas of possible enhancement are seen but were thought to represent artifact or vessels. The tiny hyperintense focus in the right temporal lobe (arrow in a) is within an area of artifact and was thought to be artifactual or related to a vessel. The hyperintense focus in the left occipital lobe (arrow in b) was seen only on coronal images and therefore was of only low suspicion and was thought to probably represent a vessel. (c, d) Contrast-enhanced axial T1-weighted MR image (similar level and same parameters as in a) (c) and coronal T1-weighted MR image (same level and parameters as in b) (d) (both obtained April 22, 1998) show definite lesions (arrow), which appear as small enhancing nodules.

 


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  		Figure 3d.   Small, rapidly growing metastases in a 49-year-old man with multiple pigmented lesions all over his body. A melanoma was resected from his upper back 1 year earlier (April 16, 1997). (a, b) Contrast-enhanced axial T1-weighted MR image of the inferior temporal lobes (a) and coronal T1-weighted MR image of the posterior occipital lobes (b) (750/20, one signal acquired) (both obtained March 4, 1998) show two subtle lesions. Tiny areas of possible enhancement are seen but were thought to represent artifact or vessels. The tiny hyperintense focus in the right temporal lobe (arrow in a) is within an area of artifact and was thought to be artifactual or related to a vessel. The hyperintense focus in the left occipital lobe (arrow in b) was seen only on coronal images and therefore was of only low suspicion and was thought to probably represent a vessel. (c, d) Contrast-enhanced axial T1-weighted MR image (similar level and same parameters as in a) (c) and coronal T1-weighted MR image (same level and parameters as in b) (d) (both obtained April 22, 1998) show definite lesions (arrow), which appear as small enhancing nodules.

 


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  		Figure 4a.   Small, rapidly growing metastases in a 31-year-old woman in whom a malignant melanoma of the right thigh was diagnosed in May 1995 (Clark level IV, 4 mm thick). (a) Contrast-enhanced axial T1-weighted MR image (500/24, one signal acquired) (obtained June 13, 1997) shows subtle foci of enhancement along the margins of the lateral ventricles (arrows). These foci could easily be mistaken for the normal vessels that are often seen in this location. (b) Axial T2-weighted MR image (4,500/95, one signal acquired) (obtained June 13, 1997) shows the foci as subtle protrusions into the cerebrospinal fluid (arrows), which could still be normal vessels. (c) Contrast-enhanced axial T1-weighted MR image (600/17, one signal acquired) of the superior aspects of the bodies of the lateral ventricles (obtained September 9, 1997) shows much larger subependymal nodules (arrows).

 


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  		Figure 4b.   Small, rapidly growing metastases in a 31-year-old woman in whom a malignant melanoma of the right thigh was diagnosed in May 1995 (Clark level IV, 4 mm thick). (a) Contrast-enhanced axial T1-weighted MR image (500/24, one signal acquired) (obtained June 13, 1997) shows subtle foci of enhancement along the margins of the lateral ventricles (arrows). These foci could easily be mistaken for the normal vessels that are often seen in this location. (b) Axial T2-weighted MR image (4,500/95, one signal acquired) (obtained June 13, 1997) shows the foci as subtle protrusions into the cerebrospinal fluid (arrows), which could still be normal vessels. (c) Contrast-enhanced axial T1-weighted MR image (600/17, one signal acquired) of the superior aspects of the bodies of the lateral ventricles (obtained September 9, 1997) shows much larger subependymal nodules (arrows).

 


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  		Figure 4c.   Small, rapidly growing metastases in a 31-year-old woman in whom a malignant melanoma of the right thigh was diagnosed in May 1995 (Clark level IV, 4 mm thick). (a) Contrast-enhanced axial T1-weighted MR image (500/24, one signal acquired) (obtained June 13, 1997) shows subtle foci of enhancement along the margins of the lateral ventricles (arrows). These foci could easily be mistaken for the normal vessels that are often seen in this location. (b) Axial T2-weighted MR image (4,500/95, one signal acquired) (obtained June 13, 1997) shows the foci as subtle protrusions into the cerebrospinal fluid (arrows), which could still be normal vessels. (c) Contrast-enhanced axial T1-weighted MR image (600/17, one signal acquired) of the superior aspects of the bodies of the lateral ventricles (obtained September 9, 1997) shows much larger subependymal nodules (arrows).

 
Miliary
Rainov and Burkert (7) report a case of miliary brain metastases from malignant melanoma in a 31-year-old woman. Five and one-half years after resection of the primary lesion, multiple brain metastases developed, which were located predominantly in the cortex and at the gray matter–white matter junction. These authors mention that the lesions were somewhat larger than in previously reported cases of miliary metastases from other primary tumors. The figures in their article show numerous, predominantly peripherally located lesions, with additional lesions in the lentiform nuclei.

Subependymal
Melanoma occasionally manifests with a subependymal pattern of spread (Fig 4). Vannier et al (8), in a report of three cases of subependymal metastases from small-cell carcinomas of the lung, describe the appearance at pathologic analysis as smooth or nodular. In two cases, contrast-enhanced computed tomography (CT) showed a somewhat nodular periventricular area of high attenuation, with a hyperattenuating nodular mass in one case and diffuse, periventricular, ribbonlike hyperattenuating areas with marked enhancement in the other case. At pathologic analysis, there was spreading beneath the ependyma with occasional areas of disruption. These authors state that the mechanism remains hypothetical; however, they suggest that, since gliomas can spread in this manner, this method of spread may be more common in cancers of neural crest origin, such as melanomas and small-cell carcinoma of the lung.

McGeachie et al (9) report four cases of periventricular spread. Three of the cases are primary brain tumors, but the fourth is a presumed metastatic melanoma. These authors mention two mechanisms for spread of tumor along the ventricles. One method is via the subependymal space, and the second is seeding in the subarachnoid space. These authors also mention that the CT appearance of periventricular spread is typical. On contrast-enhanced images, there is a thin or thick rim of high attenuation surrounding all or part of the ventricular system.


   Locations
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Usual Appearances
 Other Appearances
 Locations
Conclusions
 References
 
In a large study of patients with metastatic melanoma, Das Gupta and Brasfield (10) found that 41 of 105 (39%) had brain metastases at autopsy. Most patients with brain metastases had multiple lesions, and cerebral lesions were more common than cerebellar lesions. Only two patients had a single lesion, and one had "massive infiltration of the cortex bilaterally." One patient had a metastasis to the choroid plexus, five had dural metastases, and six had pituitary metastases.

Amer et al (11) studied 53 patients who underwent a thorough examination of the brain, dura, and spinal cord at autopsy and found that 75% had gross evidence of metastases to at least one of these structures. This group included 36 patients (68%) with metastases to the brain. Meningeal involvement was found in 28 patients (53%). There was a statistically significant lower prevalence of central nervous system metastases in patients with lower limb primary tumors than in patients with primary tumors elsewhere.

Mendez and Del Maestro (12) studied 55 patients who developed signs and symptoms of brain metastases out of a total population of 652 patients with a diagnosis of melanoma. They found that 33 patients had multiple metastases and 22 had solitary metastases. However, owing to the methods used in this study, the prevalence of undiscovered metastases may have been relatively high.

Bone
Bone metastases from melanoma are not uncommon (Fig 5), although radiographic demonstration of such metastases is relatively infrequent (13). In a study by Stewart et al (13), radiographs and bone scans demonstrated skeletal lesions in 116 of 1,677 patients (6.9%). These authors did not routinely perform screening in their patients, so there is a good chance that the true prevalence was much higher. Seventy percent of the lesions in this series involved the axial skeleton. Selby et al (14) found that 49% of patients with terminal melanoma had bone metastases. In an autopsy study, McNeer and Das Gupta (15) found that 30%–40% of patients had bone metastases.



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  		Figure 5a.   Metastasis to the clivus in a 56-year-old woman who was treated for a primary melanoma of the left globe 2 years earlier. Additional staging performed before acquisition of these images showed diffuse metastatic disease to the lungs, liver, and abdominal wall; subcutaneous nodules; a 1.8-cm-diameter pontine lesion; and multiple bone metastases, including metastases to the spine. (a) Nonenhanced sagittal T1-weighted MR image (550/25, two signals acquired) shows a hypointense lesion within the clivus (arrows), with upward bowing of the floor of the sella and mild extension into the sphenoid sinus as well as posteriorly. (b) Contrast-enhanced axial T1-weighted MR image (620/10, three signals acquired) shows enhancement of the pontine metastasis (crossed arrow) and of the clival lesion (regular arrow).

 


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  		Figure 5b.   Metastasis to the clivus in a 56-year-old woman who was treated for a primary melanoma of the left globe 2 years earlier. Additional staging performed before acquisition of these images showed diffuse metastatic disease to the lungs, liver, and abdominal wall; subcutaneous nodules; a 1.8-cm-diameter pontine lesion; and multiple bone metastases, including metastases to the spine. (a) Nonenhanced sagittal T1-weighted MR image (550/25, two signals acquired) shows a hypointense lesion within the clivus (arrows), with upward bowing of the floor of the sella and mild extension into the sphenoid sinus as well as posteriorly. (b) Contrast-enhanced axial T1-weighted MR image (620/10, three signals acquired) shows enhancement of the pontine metastasis (crossed arrow) and of the clival lesion (regular arrow).

 
In a study of the frequency of bone metastases from melanoma at CT, Patten et al (16) reviewed the results of 464 body CT studies of 125 patients. In 17 patients, skeletal metastases were found on the CT scans. The lesions were all predominantly osteolytic, and nine patients had associated soft-tissue masses. In this study, images obtained with bone windows were available in only 5% of the patients; thus, the true prevalence may have been higher. Fon et al (17) evaluated the radiographic appearance of bone lesions in 50 patients from a population of 1,870 patients who underwent scintigraphy between 1970 and 1980 and whose surgery and pathology reports mentioned melanoma. Eighty percent of the lesions were in the axial skeleton, and the vast majority were osteolytic.

Barnes et al (18) report a single case of a primary melanoma of the petrous apex of the temporal bone. They state that this entity is extremely rare.

Muscle
Metastases from all primary tumors to skeletal muscle are uncommon (Fig 6). A recent article by Herring et al (19) reports only 15 cases treated over an 18-year period, two of which were from melanoma. This study involved patients who had masses at presentation and therefore did not provide a true measure of the prevalence. These authors also reviewed the literature and found a total of only 52 additional cases. Autopsy series suggest a higher prevalence, with metastases to muscle occurring in 16% of 38 cancer patients in a study by Pearson (20). However, this author does not mention whether any of the 38 cancer patients had melanoma.



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  		Figure 6.   Presumed metastasis to the left pterygoid muscles in a 69-year-old woman in whom malignant melanoma of the vulva had been diagnosed. Nonenhanced axial T1-weighted MR image (800/16, one signal acquired) shows a slightly hyperintense lesion involving both left pterygoid muscles (arrow). The mass showed little enhancement after administration of contrast material.

 
Only a few cases of melanoma metastatic to muscle have been reported in the literature. These include the two cases in the study by Herring et al (19); a case of melanoma in the temporalis muscle in a patient with no known primary tumor (21); a case of multiple tiny nodules in the abdominal wall and extremities in a patient with widespread metastases from a malignant melanoma of the vulva (22); and a case of melanoma in a sartorius graft, which was placed afterresection of metastases to lymph nodes in the groin from a primary tumor of the foot (23). In this last case (23), the authors postulate that the mechanism was direct spread to the muscle rather than hematogenous seeding.

In addition, melanoma metastatic to the extraocular muscles has been reported, including two cases reported by DiBernardo et al (24), who described their ultrasonographic (US) appearance. A case of a metastasis to the right medial rectus muscle in a patient with facial melanoma was reported by Patel et al (25). They mention that only 11 cases of orbital metastases from malignant melanoma had been reported in the literature as of 1991. One case of a melanoma that presumably arose from an axillary lymph node sinus and that metastasized to the left medial rectus muscle was reported by Goldberg et al (26). They cite 20 cases (including theirs) of metastases to extraocular muscles and state that 10 cases (50%) were from cutaneous melanoma (26).

Nasopharynx and Mucosa
Malignant melanomas of the nasopharynx or nasal cavity are uncommon, making up no more than 0.6%–0.9% of all melanomas (6). In a review of 1,546 cases of melanoma that occurred between 1930 and 1948, Moore and Martin (27) analyzed 26 cases of primary melanoma of the mucous membranes of the oral cavity or upper respiratory tract, which accounted for only 1.7% of all cases. Most occurred in the 6th decade of life, with an average patient age of 59 years. There were no cases in the nasopharynx and only four in the oropharynx. The lesions of the oropharynx had a poor prognosis, with early metastases and rapid progression to a fatal outcome.

Mucosal melanoma is relatively more common in Japan (28). Yoshioka et al (29) retrospectively reviewed the MR images of six patients with biopsy-proved malignant melanoma of the head and neck. All of these lesions were presumably primary, since it was stated that none had a known background of cutaneous melanoma. All of the lesions were hyperintense on T1-weighted images; on T2-weighted images, five had mixed signal intensity and one had intermediate signal intensity. The article shows the images of two cases of melanoma of the nasopharynx, which have an appearance similar to that of our case (Fig 7).



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  		Figure 7.   Nasopharyngeal metastasis in a 59-year-old man with widely metastatic malignant melanoma. Contrast-enhanced axial T1-weighted MR image (750/20, one signal acquired) shows a moderately hyperintense mass in the right side of the nasopharynx (black arrow). This mass is presumably causing the right mastoid disease (white arrow). Also note the small, slightly hyperintense lesion in the left temporalis muscle (arrowhead). After administration of contrast material, the lesion blended with the adjacent mucosa.

 
In contrast, Hammersmith et al (6), in a study of five cases of nasopharyngeal and paranasal sinus melanoma, found that the dominant portions of four of the tumors were hypointense on T1-weighted images and hyperintense on T2-weighted images. Extremely variable amounts of paramagnetic substances were present, including both melanin and products of hemorrhage. These authors state that the T1 shortening more often appeared to be a reflection of the paramagnetic effects associated with the products of hemorrhage rather than the presence of melanin. Only one case was imaged during the initial presentation of the patient; this fact could have affected the imaging appearance.

Parotid Gland
Involvement of the parotid gland by metastases is not uncommon. Metastases are most commonly due to malignant melanoma of the head, most often the temporal region, or squamous cell carcinoma (30). In a study of parotid gland metastases, Conley and Arena (30) found 81 cases. Of these, 37 were from melanoma, with most of the cases having a primary tumor in the temple region; the next most common sites were the external ear and scalp. Thirty cases were from squamous cell carcinoma, with the remainder representing metastases from other neoplasms. These authors state that the parotid gland contains 20–30 lymph follicles and lymph nodes and that lymph may enter the gland directly without involvement of the paraglandular lymph nodes, may be secondarily deposited from a paraglandular node, or may come from retrograde extension from metastases in the neck. They also state that the anterior portion of the gland is rarely involved as a metastatic focus by parenchymal or paraglandular lymph nodes and that melanoma has a predilection for the paraglandular nodes (Fig 8).



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  		Figure 8a.   Paraglandular parotid metastases in a 41-year-old man with a growth in the left temporal region that appeared 2 months before imaging was performed. He developed a left facial palsy, and further staging done at that time showed metastases to the lungs and liver. (a) Nonenhanced axial T1-weighted MR image (750/20, one signal acquired) shows a mass (arrows), which is mildly hyperintense relative to the adjacent parotid gland. There was no definite enhancement after contrast material administration. (b) Axial T2-weighted MR image (7,000/112, one signal acquired) shows that the lesion (arrows) is hypointense relative to the parotid gland. (c) Nonenhanced coronal T1-weighted MR image (750/20, one signal acquired) shows multiple masses (arrows) related to and adjacent to the parotid gland. The masses are hyperintense relative to the gland. Many of these nodes are probably paraglandular, which is the more common site of involvement (30).

 


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  		Figure 8b.   Paraglandular parotid metastases in a 41-year-old man with a growth in the left temporal region that appeared 2 months before imaging was performed. He developed a left facial palsy, and further staging done at that time showed metastases to the lungs and liver. (a) Nonenhanced axial T1-weighted MR image (750/20, one signal acquired) shows a mass (arrows), which is mildly hyperintense relative to the adjacent parotid gland. There was no definite enhancement after contrast material administration. (b) Axial T2-weighted MR image (7,000/112, one signal acquired) shows that the lesion (arrows) is hypointense relative to the parotid gland. (c) Nonenhanced coronal T1-weighted MR image (750/20, one signal acquired) shows multiple masses (arrows) related to and adjacent to the parotid gland. The masses are hyperintense relative to the gland. Many of these nodes are probably paraglandular, which is the more common site of involvement (30).

 


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  		Figure 8c.   Paraglandular parotid metastases in a 41-year-old man with a growth in the left temporal region that appeared 2 months before imaging was performed. He developed a left facial palsy, and further staging done at that time showed metastases to the lungs and liver. (a) Nonenhanced axial T1-weighted MR image (750/20, one signal acquired) shows a mass (arrows), which is mildly hyperintense relative to the adjacent parotid gland. There was no definite enhancement after contrast material administration. (b) Axial T2-weighted MR image (7,000/112, one signal acquired) shows that the lesion (arrows) is hypointense relative to the parotid gland. (c) Nonenhanced coronal T1-weighted MR image (750/20, one signal acquired) shows multiple masses (arrows) related to and adjacent to the parotid gland. The masses are hyperintense relative to the gland. Many of these nodes are probably paraglandular, which is the more common site of involvement (30).

 
Other authors have also discussed metastases to the parotid gland (31–33). Roberts and Jayaramachandran (31) report a case in a patient with a 6-month history of parotid swelling. He was operated on 4 months later and was found to also have a mass below the mandible on the right side. The metastases were determined to be from a pathologically proved regressed melanoma at the hairline on the right side of the forehead. Laudadio et al (32) report cases in three patients who underwent parotidectomy for parotid masses that were not suspected to be melanoma before surgery. Subsequent history taking revealed prior resection of a melanoma of the anterior neck in one case, spontaneous regression of a temporal scalp lesion in another case, and no evidence of a prior melanoma in the third case.

There have been few reports of melanoma arising primarily in the parotid gland (34–36). Greene and Bernier (36) examined five cases of primary parotid melanoma from the Armed Forces Institute of Pathology to develop criteria for establishing a tumor as primary. These criteria are (a) the presence of dopa-positive cells in normal parotid tissue, (b) demonstration ofmalignant melanoma in the parotid gland, and (c) inability to demonstrate any other primary sites. These authors mention that melanoblasts should be present in the embryonic parotid gland because it is an outgrowth of the oral epithelium, and they found dopa-positive cells in the normal parotid glands of dogs and humans. Metastatic lesions appeared in intraparotid lymph nodes or as well-defined lesions in the parotid tissue, whereas primary lesions were infiltrative and poorly demarcated or completely replaced the parotid tissue. These authors state that it is important to define a lesion as primary versus metastatic because primary lesions are potentially amenable to therapy.

Jennings et al (37) report five cases in which desmoplastic malignant melanoma involved the parotid gland. They describe desmoplastic melanoma as an unusual variant of malignant melanoma characterized by a spindle cell morphology and a variable stromal fibrotic response. In four of their cases, local recurrences occurred following cutaneous lesions but prior to development of the parotid lesions. At histologic analysis, these cases demonstrated diffuse invasion of the parotid gland, with a tendency for spread peripherally along the septa of parotid lobules. These authors believe that the spread into the parotid gland in their cases was along nerves and less likely related to spread along lymphatic vessels.

Bahar et al (35) report a case of primary melanoma of the parotid gland and review the literature, finding 13 documented cases. They mention that in all of the reviewed cases, the main clinical manifestation was a progressively enlarging, asymptomatic mass in the area of the parotid gland, usually firm and fixed. There was initial persistent facial nerve paralysis in only one case.

Meninges
Dural involvement by malignant melanoma is rare (Fig 9). There are a few reported cases of primary dural malignant melanoma, with the majority occurring in patients who also had pigmented cutaneous nevi (38–41). Theunissen et al (39) report a case and review nine additional cases of malignant melanoma of the meninges in patients with a nevus of Ota. Their case and half of the cases reported in the literature had a dural attachment. Ozden et al (41) report two cases of dural melanomas that arose in the spine and cite five other cases of primary dural melanoma from the literature, including one case that was intracranial (Narayan et al [40]). In two of these cases, there were additional nonmalignant pigmented lesions: neurocutaneous melanosis in one case and pigment deposits in the liver and spleen in the other. Narayan et al (40) report a case of a presumed primary malignant melanoma that arose from the dura in the right cerebellopontine angle. The dura was reportedly diffusely pigmented, but the leptomeninges were noted to be normal appearing.



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  		Figure 9a.   Dural metastases in a patient in whom ocular melanoma was diagnosed in 1996. (a) Contrast-enhanced coronal T1-weighted MR image (660/17, one signal acquired) (obtained June 30, 1997) shows a 1-cm-diameter right parasagittal frontal mass (arrow), which was thought to be a meningioma. Note the normal-appearing sellar and suprasellar regions. (b) Contrast-enhanced coronal T1-weighted MR image (750/20, one signal acquired) (obtained March 10, 1998) shows enlargement of the right frontal parafalcine mass (regular arrow) and a new mass of the suprasellar region or tuberculum sellae (crossed arrow). The parafalcine mass was removed in April and was found to be a malignant melanoma at histologic analysis. In May, the suprasellar lesion, which had grown, was also removed and proved to have similar histologic features. At autopsy, there was recurrent or residual melanoma in the suprasellar location, as well as an additional dural deposit.

 


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  		Figure 9b.   Dural metastases in a patient in whom ocular melanoma was diagnosed in 1996. (a) Contrast-enhanced coronal T1-weighted MR image (660/17, one signal acquired) (obtained June 30, 1997) shows a 1-cm-diameter right parasagittal frontal mass (arrow), which was thought to be a meningioma. Note the normal-appearing sellar and suprasellar regions. (b) Contrast-enhanced coronal T1-weighted MR image (750/20, one signal acquired) (obtained March 10, 1998) shows enlargement of the right frontal parafalcine mass (regular arrow) and a new mass of the suprasellar region or tuberculum sellae (crossed arrow). The parafalcine mass was removed in April and was found to be a malignant melanoma at histologic analysis. In May, the suprasellar lesion, which had grown, was also removed and proved to have similar histologic features. At autopsy, there was recurrent or residual melanoma in the suprasellar location, as well as an additional dural deposit.

 
In meningeal melanoma, the leptomeninges are involved more commonly than the dura (38–42). The leptomeninges have the most melanocytes in the central nervous system; therefore, it follows that most melanomas occur there. The melanomas can be associated with benign pigmentation of the leptomeninges (melanosis) or cutaneous pigmented lesions (neurocutaneous melanosis) (38,41). There is little discussion of melanoma metastatic to the dura in the literature.

Choroid Plexus
Metastases to the choroid plexus are uncommon (Fig 10). Das Gupta and Brasfield (10) found only one case of choroid plexus metastases at autopsy among 105 patients with stage III melanoma or extraregional metastases.



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  		Figure 10.   Metastasis to the choroid plexus in a 32-year-old man in whom melanoma was diagnosed after 3 days of headaches. CT of the head performed at that time showed a mass that involved the choroid plexus and innumerable pulmonary nodules as well as liver metastases. The choroid plexus lesion was treated with a gamma ray knife. Posttreatment contrast-enhanced axial CT scan of the trigones of the lateral ventricles shows an enhancing mass involving the left choroid plexus (arrows). The mass is smaller than it was before therapy with the gamma ray knife.

 
Lana-Peixoto et al (43) report a case of a malignant melanoma of the choroid plexus, which they assumed was a primary tumor. At CT, the lesion was hyperattenuating. Beatty (44) reports a case of a choroid plexus melanoma in an 8-year-old boy who presented with headaches, lethargy, and poor concentration. This author found a melanoma that arose from the choroid plexus of the left lateral ventricle. The author examined the whole body (except the eyes) for a primary tumor and assumed that the choroid plexus lesion was the primary lesion. Arbelaez et al (45) describe the MR imaging findings in a case of presumed primary melanoma of the choroid plexus and suggest a possible cause. They suggest that melanocytes, which were originally located in the pia mater, arrive in the choroid plexus due to formation of the choroid plexus from a core of blood vessels surrounded by pia mater and ependymal cells. The melanoma in their case was hyperattenuating at CT, had a hyperintense rim on T1-weighted images, was relatively hypointense on T2-weighted images, and demonstrated heterogeneous enhancement.

Kohno et al (46) report three cases in which solitary metastases to the choroid plexus were the only manifestation of intracranial involvement in patients with extracranial primary neoplasms. They also found eight similar cases of solitary metastases in the literature. None of these case were of melanoma, although one case had an unknown primary tumor. These authors found a total of 18 reported cases in the literature of tumors metastatic to the choroid plexus. Schreiber et al (47) studied 737 patients with extracranial primary tumors and found choroid plexus metastases in 19 (2.6%) at autopsy. All of these patients except one had additional cerebral metastases or leptomeningeal involvement. Arendt and Fuchs (48) found that 5% of the patients in their study had choroid plexus metastases from extracranial primary tumors.

Internal Auditory Canal
Metastases to the internal auditory canals are uncommon, with over 99% of the lesions that occur in this location being benign (5,49). To my knowledge, there have been fewer than 10 reported cases of melanoma metastatic to the internal auditory canals and cerebellopontine angles (5,49–53). Metastatic tumors manifest differently than vestibular schwannomas, producing rapid progression of hearing loss and often rapidly developing seventh nerve and lower cranial nerve symptoms as well. In a histopathologic study of a case of widely metastatic melanoma with involvement of both internal auditory canals, Harbert et al (50) found evidence of demyelinization as well as a decreased number of axons. They found melanoma filling the orifices of the internal auditory canals and involving the entire cochlea and the round window niche, and melanoma cells were also in the endolymphatic duct and the cochlear aqueduct.

In a report of three cases (one bilateral), Arriaga et al (5) state that metastatic melanoma in the cerebellopontine angle can resemble a meningioma (as in case 3 in their article). They also mention that the four tumors in their three patients did not have the typical signal intensity of melanoma but were isointense on T1-weighted images and hyperintense on T2-weighted images.

Melanoma metastases to the internal auditory canals, like those elsewhere, can occur many years after the initial diagnosis of melanoma (Fig 11). Many of the cases occurred 5 years or more after the initial diagnosis (5,49–52).



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  		Figure 11a.   Bilateral involvement of the internal auditory canals in a woman who presented with vertigo 11 years after resection of the original melanoma on the right foot. (a) Contrast-enhanced axial T1-weighted MR image (500/20, two signals acquired) shows enhancing tissue within both internal auditory canals (arrows). This tissue was slightly hyperintense before contrast material administration. (b) Contrast-enhanced axial T1-weighted MR image (500/20, two signals acquired) of the Meckel cave shows thickening of the fifth cranial nerves and enhancement, more marked on the left side (arrow).

 


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  		Figure 11b.   Bilateral involvement of the internal auditory canals in a woman who presented with vertigo 11 years after resection of the original melanoma on the right foot. (a) Contrast-enhanced axial T1-weighted MR image (500/20, two signals acquired) shows enhancing tissue within both internal auditory canals (arrows). This tissue was slightly hyperintense before contrast material administration. (b) Contrast-enhanced axial T1-weighted MR image (500/20, two signals acquired) of the Meckel cave shows thickening of the fifth cranial nerves and enhancement, more marked on the left side (arrow).

 
Orbit
Nonocular malignant melanoma only rarely metastasizes to the orbit (Figs 12–14) (24,26). The predominant route of spread is thought to be hematologic (10,54). The most common neoplasm to metastasize to the orbit is breast carcinoma, accounting for 29%–75% of cases in several series (26). The most common primary tumor in male patients is lung cancer (25). Goldberg et al (26) performed a literature review, which included one case that they themselves had reported. They found that among 28 cases of nonocular malignant melanoma metastatic to the orbit, 10 cases (36%) were documented to have metastasized to the extraocular muscles, although the exact site of orbital involvement was not specified in all cases. Orcutt and Char (55) report six cases of orbital involvement by melanoma and review the literature on this entity. Among 21 cases of metastases to the orbit, they found that 16 had metastases to the extraocular muscles. In the six cases reported by these authors, three had extraocular muscle metastases.



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  		Figure 12a.   Orbital metastasis with involvement of the medial rectus muscle in a 50-year-old man in whom melanoma of the left shoulder and upper back was diagnosed 5-6 years earlier. (a) Nonenhanced axial CT scan (3-mm section thickness) obtained for stereotactic localization on September 23, 1997, shows a mass with attenuation similar to that of muscle in the medial aspect of the left orbit (black arrow). The mass appears to involve the medial rectus muscle (arrowhead) and extends to and slightly displaces the optic nerve (white arrow). (b) Contrast-enhanced axial T1-weighted MR image (500/15, one signal acquired) (also obtained for stereotactic localization on September 23, 1997) shows that the mass (white arrow) appears to involve the medial rectus muscle (arrowhead) and affects the optic nerve (black arrow). The mass is mildly hyperintense with respect to brain tissue.

 


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  		Figure 12b.   Orbital metastasis with involvement of the medial rectus muscle in a 50-year-old man in whom melanoma of the left shoulder and upper back was diagnosed 5-6 years earlier. (a) Nonenhanced axial CT scan (3-mm section thickness) obtained for stereotactic localization on September 23, 1997, shows a mass with attenuation similar to that of muscle in the medial aspect of the left orbit (black arrow). The mass appears to involve the medial rectus muscle (arrowhead) and extends to and slightly displaces the optic nerve (white arrow). (b) Contrast-enhanced axial T1-weighted MR image (500/15, one signal acquired) (also obtained for stereotactic localization on September 23, 1997) shows that the mass (white arrow) appears to involve the medial rectus muscle (arrowhead) and affects the optic nerve (black arrow). The mass is mildly hyperintense with respect to brain tissue.

 


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  		Figure 13a.   Eyelid metastasis in a 54-year-old woman in whom acral lentiginous melanoma of the right foot was diagnosed 11 years earlier; metastatic disease developed in 1992. At the time these images were obtained, the patient had pain during downward and straight-ahead gazing. A right upper eyelid lesion was seen at examination. (a) Nonenhanced axial T1-weighted MR image (750/20, one signal acquired) shows a small mass along the lateral aspect of the right eyelid (arrow). The mass is mildly hyperintense with respect to brain tissue. (b) Axial T2-weighted MR image (4,000/105, one signal acquired) shows that the lesion (arrow) is hypointense with respect to brain tissue.

 


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  		Figure 13b.   Eyelid metastasis in a 54-year-old woman in whom acral lentiginous melanoma of the right foot was diagnosed 11 years earlier; metastatic disease developed in 1992. At the time these images were obtained, the patient had pain during downward and straight-ahead gazing. A right upper eyelid lesion was seen at examination. (a) Nonenhanced axial T1-weighted MR image (750/20, one signal acquired) shows a small mass along the lateral aspect of the right eyelid (arrow). The mass is mildly hyperintense with respect to brain tissue. (b) Axial T2-weighted MR image (4,000/105, one signal acquired) shows that the lesion (arrow) is hypointense with respect to brain tissue.

 


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  		Figure 14a.   Probable metastasis of the globe in a 54-year-old woman in whom acral lentiginous melanoma of the right foot was diagnosed 11 years earlier; metastatic disease developed in 1992 (same patient as in Fig 13). A dome-shaped, pigmented mass with a collar-button appearance and measuring 8 x 5 mm was seen in the inferior temporal quadrant of the right globe. The mass was compatible with a primary or secondary choroidal melanoma; given the patient’s history, it was thought to most likely represent metastatic disease. (a) Contrast-enhanced axial T1-weighted MR image (750/20, one signal acquired) shows an enhancing lesion along the posterior aspect of the right globe (arrow). (b) Axial T2-weighted MR image (4,000/105, one signal acquired) shows that the lesion is hypointense (arrow).

 


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  		Figure 14b.   Probable metastasis of the globe in a 54-year-old woman in whom acral lentiginous melanoma of the right foot was diagnosed 11 years earlier; metastatic disease developed in 1992 (same patient as in Fig 13). A dome-shaped, pigmented mass with a collar-button appearance and measuring 8 x 5 mm was seen in the inferior temporal quadrant of the right globe. The mass was compatible with a primary or secondary choroidal melanoma; given the patient’s history, it was thought to most likely represent metastatic disease. (a) Contrast-enhanced axial T1-weighted MR image (750/20, one signal acquired) shows an enhancing lesion along the posterior aspect of the right globe (arrow). (b) Axial T2-weighted MR image (4,000/105, one signal acquired) shows that the lesion is hypointense (arrow).

 
In a study of the US characteristics of melanoma metastatic to the extraocular muscles, DiBernardo et al (24) describe the lesion as sparing the tendon and producing marked thickening of the muscle belly fibers. One of their two patients had unilateral involvement of one muscle, and the other had bilateral involvement of multiple muscles. In a case reported by Patel et al (25), a 60-year-old woman with a primary melanoma anterior to the tragus of the left ear had an orbital metastasis to the right medial rectus muscle, which was confirmed with radioisotope scanning. The CT appearance of this lesion was described as "spindle like swelling," and Figure 1 of their article is similar to the image of our case (Fig 12). A metastasis to the left medial rectus muscle reported by Goldberg et al (26) appeared as bulky fusiform enlargement at CT.

In an autopsy series, Das Gupta and Brasfield (10) found two cases of peri- or retro-orbital metastases with visible lesions and one case of an ocular metastasis. In a case report and review of the literature regarding ocular and orbital metastases from cutaneous melanoma, Letson and Davidorf (54) state that most of the cases included concurrent lung, liver, and central nervous system involvement, as in their case. Orcutt and Char (55) make a similar statement and mention that orbital metastases are a late event, with a mean time from presentation to death of only 3.75 months. They also mention that it is unusual for primary choroidal melanoma to manifest as metastatic disease.

De Bustros et al (56) report 10 cases of intraocular metastases from melanoma. The metastases involved the choroid in six patients (seven eyes total [one case was bilateral]), the iris in three patients (four eyes total [one case was bilateral]), and the retina unilaterally in one patient. All of the patients had concurrent systemic metastases. In a study of the CT appearance of orbital metastases (from all primary tumors, including melanoma), Healy (57) found two cases of melanoma out of 22 total cases. One of the melanoma metastases was described as both retinal and choroidal, and the other was described as involving the orbit, both intraconally and extraconally.


   Conclusions
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Usual Appearances
 Other Appearances
 Locations
 Conclusions
References
 
Malignant melanoma can have a wide variety of appearances and can involve almost any structure in the intracranial and extracranial head. Although typical signal intensity characteristics have been described for the melanotic and amelanotic patterns, there is frequent deviation from these patterns. In addition, although the brain is the most common site of metastases in the head and neck, melanoma can involve essentially any structure. Knowledge of the features of malignant melanoma in the head will aid the radiologist when screening patients with malignant melanoma for metastases.


   References
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Usual Appearances
 Other Appearances
 Locations
 Conclusions
 References
 

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