Four patients with metastasis to muscle had imaging with either CT or MRI. The primary site was renal cell adenocarcinoma in two cases, both of whom had synchronous paraspinal muscle masses. A patient with history of treated primary lung adenocarcinoma and treated primary renal adenocarcinoma developed a metastasis to the left gluteal muscles. A patient with primary extraosseous osteosarcoma in the quadriceps group developed metastasis to a hamstring muscle on the same side. We add these cases to the five non-autopsy cases reported, only one of which had cross sectional imaging (CT) documented.

Key words: muscle, metastasis, lung adenocarcinoma, renal adenocarcinoma, MRI, CT

Although skeletal muscle constitutes about 43% of the total body weight, it is a rare site for metastatic disease [1]. Primary soft tissue tumors involving muscle such as liposarcoma are more common than metastasis to muscle. Based on two autopsy studies of cancer patients, the incidence of muscle metastasis is less than one percent in patients who die of cancer [2,9]. The incidence of clinically evident metastasis to muscle is extremely rare, with only five cases reported to date [3,5-7]. We report an additional four cases with emphasis on findings by CT and MRI.

Case one- A 46 year old male presented with hematuria and right flank pain. CT demonstrated a large right renal mass and additional mass in right erector spinae muscle (Fig 1). En bloc surgical excision was accomplished with removal of muscle and kidney, pathology demonstrating renal adenocarcinoma. 18 months later the patient developed pulmonary nodules and nodules in chest wall consistent with metastatic disease.

Case two- A 51 year old male presented with back pain and hematuria. CT demonstrated a large left renal tumor, retroperitoneal adenopathy, and enlargement of right erector spinae muscle (Figs 2A, 2B). Aspirate of supraclavicular nodes demonstrated anaplastic renal adenocarcinoma. After embolization, a radical left nephrectomy was performed. CT obtained 1 month later showed enlargement of right paraspinal mass which was presumed to represent metastatic adenocarcinoma (Fig 2C).

Case three- A 61 yo male with history of previously resected primary lung adenocarcinoma and primary renal adenocarcinoma was previously in remission when presenting with severe left hip and buttock pain. MRI ordered to exclude metastasis or avascular necrosis of the left hip showed focal abnormality in the pyriformis muscle (Figs 3A-3D). Needle biopsy was performed one month later because of intractable pain and clinical suspicion for tumor, demonstrating adenocarcinoma from lung primary. MRI two days after biopsy showed worsening (Figs 3E, 3F). Patient received radiation therapy with symptomatic improvement except for left thigh pain. Two months after needle biopsy follow up MRI showed improvement in the left gluteal region and a new mass in the right thigh suspicious for another metastasis (Figs 3G-J). Biopsy of this new mass was deferred because of proximity to the sciatic nerve and radiation therapy is being given empirically.

Case 4- A 50 yo male with extraosseous osteosarcoma of right vastus lateralis was imaged with MRI (Figs 4A-4C). Focal enhancement in mid right semitendinosus muscle was noted and biopsy showed this to represent a site of "skip metastasis." Patient is receiving chemotherapy prior to surgery.

Considering that vascular embolization is a common modality for tumor metastasis and that skeletal muscle is well vascularized, the rarity of skeletal muscle metastasis is difficult to explain. One could postulate that skeletal muscle is a hostile milieu for the proliferation of cancer cells, but we could find no studies in the literature to explain why this should be true.

Autopsy studies have indicated muscle metastases which were not clinically evident. Willis found four cases of muscle metastasis in 500 cancer necropsies: two from thyroid carcinoma and two from squamous cell carcinoma of head and neck [9]. In another autopsy series of patients with renal cell carcinoma, there were three instances of muscle metastasis in 523 cadavers [2].

Case reports of muscle metastasis have included two cases from lung adenocarcinoma, two cases from adenocarcinoma of the colon, and one case from renal adenocarcinoma [3,5-7]. CT images of a metastasis to adductor muscles from lung adenocarcinoma were shown as the presenting complaint in one of these cases [7].

Many cancers are known to have a propensity for unusual manifestations. Specifically, about 30 to 45% of patients with renal carcinoma have no symptoms directly referable to their primary renal tumor, either because of distant metastasis or because of systemic symptoms [8]. A published case report of renal adenocarcinoma described a patient with metastasis to the thigh muscles five years after nephrectomy [3]. He remained disease free one year after resection of the metastasis.

Our two cases of metastasis from renal adenocarcinoma were similar in that the erector spinae muscles were involved and therefore flank pain may have been due to either the primary tumor or the muscle metastasis. Also both of our patients had advanced disease, with recurrent chest wall muscular metastases in one case.

Computed tomography has a well documented role for the evaluation of disease extent [4]. Its use in such widespread metastasizing tumors such as melanoma often reveals asymptomatic sites of disease spread [4]. More recently, and particularly in the extremities, MRI has demonstrated superb sensitivity for the detection of soft tissue pathology. CT nicely demonstrates masses such as in cases one and two. MRI will also show tissue edema without focal mass which can be due to neoplasm such as in cases three and four.

MRI can also be used in the follow up of treated metastasis and to detect asymptomatic metastasis. In case three, the left gluteal muscles were atrophied with mild diffuse gadolinium enhancement after radiation therapy. Although the initial metastasis enhanced only minimally, a suspected hamstring metastasis detected incidentally enhanced moderately with gadolinium. This was one of several instances where imaging of both extremities by using the axial and coronal planes has revealed occult disease, even though imaging of only one extremity is requested by the clinician.

Another unusual observation is that of an apparent asymptomatic "skip metastasis" in case four. Although medullary skip metastases are not unusual in cases of osteosarcoma of bone, we are not aware of soft tissue osteosarcoma metastasizing to nearby skeletal muscle.

In summary, we have added an additional 4 cases to the 5 already reported cases of muscle metastases, resulting in nine cases; three secondary to renal adenocarcinoma, two secondary to colon carcinoma, and two secondary to lung adenocarcinoma. Interesting features noted were involvement by erector spinae muscle by two cases of renal adenocarcinoma, and edematous appearance of metastasis without discrete mass on MRI in our two other cases.

1. Basmajian JV, Slonecker CE (1989) Grant's method of anatomy (11th ed). Williams and Wilkins, Baltimore. pg. 18-24

2. Bennington JL, Kradjian RM (1967) Site of metastases at autopsy in 523 cases of renal cell carcinoma. In: Renal carcinoma (chapter 6). Saunders, Philadelphia

3. Karakousis CP, Rao U, Jennings E (1981) Renal cell carcinoma metastatic to skeletal muscle mass: a case report. J Surg Onc 17:287

4. Kostrubiak I, Whitley NO, Aisner J et al (1988) The use of computed body tomography in malignant melanoma. JAMA 259:2896

5. Laurence AE, Murray AJ (1978) Metastasis in skeletal muscle secondary to carcinoma of the colon- presentation of two cases. Br J Surg 57:529

6. Sarma DP, Kovac A, Socorro N (1981) Metastatic carcinoma of the skeletal muscle. South Med J 74:484

7. Steinbaum S, Liss A, Tafreshi M, Alexander LL (1983) CT findings in metastatic adenocarcinoma of the skeletal muscles. J Comput Assist Tomogr 7:545

8. Weigensberg IJ (1971) The many faces of metastatic renal carcinoma. Radiology 98:353

9. Willis RA (1967) Pathology of tumors (4th ed). Appleton-Century-Crofts, New York. pg 163-190

1. CT without contrast during needle biopsy of right renal mass shows hypodense mass in right erector spinae muscle (arrow).

2A. CT with contrast shows left renal tumor and retroperitoneal adenopathy. There is minimal asymmetry of paravertebral muscles.

2B. Image at a higher level shows definite enlargement of right erector spinae muscle.

2C. Follow up CT without contrast shows the right erector spinae muscle has enlarged further and become hypodense, indicating an enlarging mass within (arrow).

3A. SE (600/20) axial image shows discontinuity of mid pyriformis muscle (arrow) initially considered suspicious for a muscle tear.

3B. Same sequence post gadolinium shows minimal enhancement distal portion of this muscle.

3C. Coronal SE (2000/80) shows edematous change in left pyriformis muscle, but no discrete mass.

3D. Axial gradient echo (600/18/15 deg) highlights the distal portion of the pyriformis muscle.

3E. Axial SE (2550/80) shows increase edema in gluteal muscles without any discrete mass, suggesting tumor infiltration and/or post biopsy change.

3F. Image caudad shows that edematous process surrounds the sciatic nerve (arrow).

3G. Post therapy axial SE (750/16) with gadolinium shows diffuse enhancement and atrophy of left gluteal muscles.

3H. Axial SE (750/16) right mid thigh shows mass near sciatic nerve.

3I. Same image post gadolinium shows moderate enhancement.

3J. Coronal SE (1700/70) image suggests the mass may be originating from a hamstring muscle (arrow).

4A. Axial SE (750/16) image of right thigh shows low signal mass in vastus lateralis muscle known to be osteosarcoma.

4B. Same image post gadolinium shows moderate focal enhancement in semitendinosus muscle, more than in known tumor.

4C. Coronal SE (2033/70) image shows focal edema in right hamstring muscles, but no discrete mass.