Cysts and cystic-appearing lesions of the knee: A pictorial essay

Abstract

Cysts and cystic-appearing lesions around the knee are common and can be divided into true cysts (synovial cysts, bursae, ganglia, and meniscal cysts) and lesions that mimic cysts (hematomas, seromas, abscesses, vascular lesions, and neoplasms). The specific anatomic location of the cystic lesion often permits the correct diagnosis. In difficult cases, identifying a cystic mass in an atypical location and/or visualizing internal solid contrast enhancement on magnetic resonance imaging (MRI) should raise concern for a neoplasm and the need for further evaluation and intervention.

Keywords: Bursa; cyst; knee; synovial cyst.

Conflict of interest statement

Conflict of Interest: None declared.

Figures

Figure 1(A-C)

Popliteal cyst. A 60-year-old female with knee pain. (A) Lateral knee radiograph demonstrates coarse calcifications (arrow) in the popliteal fossa. (B) Gray scale USG image at the level of popliteal fossa demonstrates a cystic lesion containing echogenic calcifications (arrow) with posterior acoustic shadowing. (C) Axial T2W image through right knee demonstrates the hyperintense popliteal cyst fluid arising between semimembranosus (arrowhead) tendon and medial head of gastrocnemius (asterisk), with hypointense loose bodies (arrow) layering dependently

Figure 2(A-C)

PTFJ cyst. A 50-year-old male with palpable mass. Axial T1W MR image (A) demonstrates uniformly hypointense mass (arrow) with small tail (arrowhead), arising from proximal tibiofibular joint. Lesion (arrow) is hyperintense on coronal short tau inversion recovery (STIR) MR image (B) and does not enhance on post-contrast T1W fat-saturated image (C)

Figure 3(A, B)

PTFJ cyst. A 57-year-old man with foot drop. Axial proton density (PD) image (A) shows large cyst (arrows) compressing the common peroneal nerve (arrowhead). There is muscle edema (arrow) in anterior tibialis on the axial STIR image (B)

Figure 4

Semimembranosus/tibial collateral ligament bursa. A 45-year-old woman with posteromedial knee pain. Sagittal T2W fat-saturated image demonstrates a tubular bright cystic mass (arrow) just posterior to the semimembranosus tendon (arrowhead) (image courtesy of Dr. Justin Kung, Boston, MA)

Figure 5(A, B)

Prepatellar bursitis. A 16-year-old female with anterior knee pain. (A) T2W fat-saturated image demonstrates enlarged fluid-filled space in prepatellar region (arrows) with surrounding fat stranding. (B) T1W post-contrast image demonstrates only peripheral enhancement (arrows)

Figure 6

Infrapatellar bursitis. A 28-year-old male with anterior knee pain. Sagittal fat-saturated T2W image shows triangular pocket of fluid (arrow) between distal patellar tendon and anterior tibia. There is also bone contusion in lateral femoral condyle and fluid in suprapatellar recess (arrowheads), resulting from transient lateral patellar dislocation

Figure 7(A and B)

Iliotibial band cyst. A 46-year-old man with palpable abnormality. (A) Coronal T2W fat-saturated image demonstrates well-circumscribed hyperintense cyst (arrows) abutting the iliotibial band, which does not enhance internally following contrast administration on the post-contrast T1W fat-saturated image (B)

Figure 8(A, B)

Pes anserine bursitis. A 30-year-old male with medial knee pain. (A) Axial T2W and (B) sagittal T2W fat-saturated images demonstrate fluid signal (arrows) adjacent to the insertion of the pes anserine tendons

Figure 9

Medial collateral ligament bursitis. A 56-year-old man with medial knee mass and pain. Coronal T2W fat-saturated image shows an oblong heterogeneous cystic mass (arrow) adjacent to the medial collateral ligament (arrowhead)

Figure 10(A-C)

Gastrocnemius ganglion. A 45-year-old male with knee pain. Sagittal PDW image (A) demonstrates lobulated lesion (arrows) at insertion of medial head of gastrocnemius that is hyperintense on sagittal (B) and coronal (C) T2W fat-saturated images

Figure 11(A, B)

Popliteus ganglion. A 34-year-old woman with knee pain. (A) Axial and (B) sagittal T2W fat-saturated images show a cystic lesion (arrow) in the popliteus tendon sheath

Figure 12(A, B)

ACL ganglion. A 31-year-old male with knee pain. (A) Sagittal PDW and (B) T2W fat-saturated images demonstrate cystic lesion in proximal fibers of anterior cruciate ligament (arrows), which expands ligament fibers and produces “drumstick” appearance. Note the presence of continuous intact ACL fibers

Figure 13

PCL ganglion. A 28-year-old male with persistent pain after injury. Sagittal T2W fat-saturated image demonstrates multilobulated cystic lesion (arrow) involving distal posterior cruciate ligament

Figure 14(A, B)

Meniscal cyst. A 42-year-old female with knee pain and palpable lateral mass. (A) Coronal PDW image of the right knee demonstrates a multilobulated cyst (arrow) with internal septations, which arises from tear of body of lateral meniscus. (B) T2W fat-saturated image demonstrates cystic nature of this lesion (arrow), which did not enhance following contrast administration (not shown)

Figure 15(A-D)

Hematoma. A 46-year-old male with pain and swelling after fall. (A) Sagittal T1W image demonstrates a hyperintense lesion (arrows) with hypointense rim and surrounding fat stranding. Axial pre (B) and post (C) T1W fat-saturated, and subtracted post-contrast images (D) confirm lack of enhancement. Crescentic misregistration artifact is seen at the lateral aspect of the hematoma

Figure 16(A-C)

Seroma. A 71-year-old female with swelling following total knee arthroplasty. (A) Coronal T1W and (B) T2W fat-saturated images demonstrate linear fluid collection (arrows) along the lateral aspect of knee. (C) Post-contrast axial subtraction image shows rim enhancement only (arrows). Percutaneous needle drainage yielded non-infected serous fluid

Figure 17(A-C)

Abscess. A 14-year-old female with fever and knee pain. (A) Sagittal T2W fat-saturated image demonstrates hyperintense mass (arrows) with surrounding soft-tissue edema in popliteal fossa. Axial (B) pre-and (C) post-contrast T1W images show peripheral enhancement (arrows) with lack of central enhancement

Figure 18(A-C)

Popliteal artery aneurysm. A 62-year-old male with pulsatile mass in popliteal fossa. (A) Sagittal T2W fat-saturated image demonstrates heterogeneous mass in the region of popliteal fossa (arrows). (B) Digital subtraction angiography shows partial thrombosis of large popliteal fossa aneurysm (arrows), which was subsequently embolized with coils (arrowheads) (C)

Figure 19(A, B)

Intramuscular hemangioma. A 54-year-old female with knee mass and pain. (A) Sagittal T2W fat-saturated and (B) axial T1W fat-saturated post-contrast images show a lobulated enhancing cystic mass (arrows) in the vastus medialis

Figure 20(A, B)

Lymphatic malformation. A 23-year-old female with palpable medial knee mass. (A) Coronal T1W image shows multilobulated cystic lesion (arrows) in the medial aspect of the knee that is isointense and hyperintense to muscle. (B) Axial fat-suppressed T2W image shows fluid-fluid levels (arrow) in this multicystic lesion

Figure 21

Venous varix. A 57-year-old female with knee pain. Axial post-contrast T1W fat-saturated image demonstrates lobulated vascular structure (arrows) draining into the popliteal vein

Figure 22(A-C)

Necrotic bladder cancer soft-tissue metastasis. A 65-year-old man with knee pain. (A) Coronal T2W fat-saturated and (B) axial T2W images show a cystic mass (arrows) in the vastus medialis with surrounding edema. (C) Axial T1W fat-saturated post-contrast image shows thick rim enhancement (arrow) and a lack of central enhancement due to tumor necrosis

Figure 23(A-D)

Schwannoma. A 38-year-old male with knee pain. Axial (A) T1W and (B) T2W fat-suppressed images show T2-hyperintense lesion (arrows) in the lateral soft tissue of the knee. (C) Coronal PDW image confirms that the mass (arrow) arises from common peroneal nerve (arrowheads). (D) Photomicrograph [hematoxylin and eosin (H and E), ×400] shows alternating hypocellular and hypercellular spindle cells with Verocay bodies and cytologically bland spindle cells with plump nuclei, consistent with a schwannoma

Figure 24(A-C)

Synovial sarcoma. A 23-year-old male with palpable mass. (A) Sagittal T1W image demonstrates hypointense oblong mass in semimembranosus muscle (arrow), which has solid internal enhancement (arrow) on post-contrast T1W fat-saturated image (B). (C) Photomicrograph (H and E, ×200) shows a highly cellular spindle cell neoplasm composed of densely packed cells with scant cytoplasm. The tumor is characterized by its lack of nuclear pleomorphism and a mitotic rate that is lower than expected for such a cellular tumor, consistent with a synovial sarcoma

Figure 25(A-C)

Juxta-articular myxoma. A 27-year-old female with palpable abnormality. (A) Axial T1W image shows well-circumscribed, ovoid cystic lesion in medial subcutaneous tissues that is hyperintense on the (B) axial T2W fat-saturated image. (C) Sagittal post-contrast T1W fat-saturated MR image shows solid internal enhancement (arrow)