Lipoma

DEFINITION AND PATHOGENESIS

• Classification

• • Lipoma
    • Superficial (esp back, shoulders, neck, abdomen)
    • Deep (intramuscular, intermuscular, lumbosacral, perineural, lipoma of tendon sheath)
    • Intraarticular--not lipoma arborescens
  • Lipoma variants
    • Angiolipoma
    • Spindle cell lipoma
    • Pleomorphic lipoma
    • Benign lipoblastoma/lipoblastomatosis
    • Angiomyolipoma
    • Angiolipoma
    • Angiomylipoma
    • Chondroid lipoma
    • Lipomatosis
    • Myolipoma
    • Extra-adrenal myelolipoma
    • Extrarenal angiomyolipoma
    • Hibernoma
  • Lipomas intimately associated with other tissues
    • Intramuscular (infiltrating)
    • Intermuscular lipoma
    • Lipoma of tendon sheath (endovaginal lipoma)
    • Involving major nerves of the hand and wrist
      • Fibrolipomatous hamartoma
      • Neural fibrolipoma
      • Perineural lipoma
    • Lumbosacral lipoma
    • Periosteal (juxtacortical) lipoma
    • Involving the synovium (villous, lipomatous proliferation of the synovial membrane, lipoma arborescens)
    • Involving the bronchial tract
    • Intravascular lipoma
      • Intracardiac lipoma
    • Lipomas associated with the GI tract
      • Gastric lipoma
        • Reported in a 12-year-old boy
  • Infiltrating proliferations of mature fat
    • Diffuse lipomatosis
    • Pelvic lipomatosis
    • Cervical symmetrical lipomatosis (Madelung's disease)
    • Adiposis dolorosa (Dercum's disease)
    • Steroid lipomatosis
  • Hibernoma (brown fat such as in hibernating animals)

IMPORTANCE

• Most common tumor of soft tissue

CLINICAL FEATURES

• Most common neoplasm of mesenchymal origin
• Rare first two decades
• M=F
• Asymptomatic, slow-growing, round or discoid mass having a soft or doughy consistency (hardens after application of ice), rarely painful (except angiolipoma, most often forearm lesions)
• Lipoma of tendon sheath occurs distally (50% bilateral)
• Spindle cell and pleomorphic lipomas characteristically in male patients between 45-65 in the posterior neck and shoulder, painless and slowly growing
• Lipomatous proliferation of the synovial membrane may be bilateral (?20%), of long-standing duration, and associated with DJD, DM, popliteal cysts (20%), joint trauma, psoriatic arthritis (knee most common, also wrist, shoulder, hip, subdeltoid bursa)
• Average age 41 (9-90)
• M:F = 1.3:1
• Different than an intraarticular lipoma
• Young to middle-aged BMs most often affected in pelvic lipomatosis
• Intraneural fibrolipoma infiltrates large peripheral nerves (33% associated with macrodactyly/fatty overgrowth) with nerve compression sxs and gradual loss of function
• Fatty growth involving neck ("horse collar") herald's Madelung's disease with EtOH abuse
• Radicular sxs
  • Suprascapular nerve entrapment with large lipoma has been reported
• Lipomas in the hand
  • May uncommonly be associated with compression of the median nerve and CTS
    • Complete return of function can be expected after resection
  • Can be an unusual cause of macrodactyly
  • Has been reported in an anomalous lumbrical muscle belly causing CTS and 'trigger wrist'
• Lipomas of oral and maxillofacial region (in order of prevalence):
  • Parotid region
  • Buccal mucosa
  • Lip
  • Submandibular region
  • Tongue
  • Palate
  • Floor of mouth
  • Vestibule
  • Retropharyngeal
• Unusual location
  • Intracranial
    • Quadrigeminal plate cistern
      • Reported presenting with seizures
    • Can mimick hemorrhage
      • Fat-water interface prominent on MR standard TE setting on susceptibility-weighted imaging with peripheral low-signal-intensity rim in lipomas
    • Can mimick DVT
      • Pericallosal location reported mimicking deep cerebral vein thrombosis
  • Thorax 
    • Bronchus
      • Presented with chest pain and persistent cough obstructing the main bronchus in the left lobe
    • Mediastinum
      • Spindle cell lipoma reported

   

  • Cardiac
    • Interatrial location reported
      • Interatrial septal lipoma reported causing compression of the SVC
    • Intraventricular location reported
      • (Trans-aortic endoscopic excision reported)
  • Breast
    • Giant chondroid lipoma reported
  • Gastrointestinal
    • Duodenum
      • Reported presenting with gastric outlet obstruction
    • Ileum
      • Reported with recurrent ileocolic intussusceptions
    • Mesenteric
      • Recurrent intestinal obstruction reported
  • Genitourinary
    • Scrotal
      • Massive lipomas can arise from the spermatic cord

RADIOLOGIC FEATURES

• Radiolucent round soft tissue mass ? calcification
• CT and MRI reveal homogeneous fat density (both T1- and T2-weighted images)
• MRI of hibernoma, because of hypervascularity may resemble liposarcoma, esp interscapular region, neck, mediastinum, retroperitoneum
• PET
  • Mean SUVs lower than with liposarcoma
    • Cut-off value of 0.81 provides significant differentiation between benign lesions and wll-differentiated liposarcoma
• Myelolipoma occurs in the adrenals, retroperitoneum and pelvic soft tissues

GROSS PATHOLOGY

• Well delineated from surrounding tissues by a thin capsule
• Orange yellow lesion in hibernoma
• Villous fatty mass seen arthroscopically in lipoma arborescens
• Fatty frond-like appearance

HISTOLOGIC FEATURES

• Cell size varies slightly and slightly larger than mature fat cells (lipocytes have small nuclei at the periphery of the cell)
• Rich vascularity not readily discernible (except in angiolipoma, which has diagnostic intraluminal fibrin thrombi as well as ± perivascular fibrosis)
• Fibrous connective tissue may be part of tumor
• Bone marrow elements and fat cells in myololipoma
• Host tissue atrophied (muscle, nerve)
• Hibernoma has lipocytes with vacuolated cytoplasm and dark-staining nucleus
• Floret-type giant cells in pleomorphic lipoma have periperipherally placed nuclei
• Uniform spindle cells + mature fat lacking pleomorphism ± mast cells ± vascular pattern ± myxoid change
• Chondroid or osseous metaplasia is rare, calcification from infarction
• ± necrosis, hemorrhage may be associated with inflammatory cells
• Synovial lipoma with proliferation of fat within synovial villi
• Replacement of subsynovial tissue by mature fat cells
• Lumbosacral lipomas have neuroglia, ependymal elements, and smooth muscle
• Liposfuscin pigment within cytoplasm of multivacuolated brown fat cells is golden-brown in hibernoma which typically grows within striated muscle
• Special stains:
  • Trichrome highlights septae

DIFFERENTIAL CLINICOPATHOLOGIC DIAGNOSIS

• With the advent of MRI, the diagnosis is only in question when areas of inhomogeneousy are present, giving a differential of the liposarcoma variants
• Lipoma-like hibernoma
• Histologically, leiomyoma or leiomyosarcoma are confused with myolipoma and angiomyolipoma which histologically contain smooth muscle elements
• Occasionally angiosarcoma in angiolipoma
• Rhabdomyoma, granular cell tumor, and round cell liposarcoma in hibernoma
• Extramedullary hematopoiesis in myelolipoma

DISEASE COURSE AND TREATMENT

• Recurrence with marginal excision is <5% (0-80% reported) (esp intramuscular lipoma which infiltrates skeletal muscle), and malignant changes are reportable
• Marginal (not intralesional) resection recommended
• Excision is never as easy as when first diagnosed
• Multiple lesions in 5-6% of patients (small % with familial multiple lipomas), multiple angiolipomas are more common than solitary ones, are painful, and most commonly are in the forearm
• Lipomatosis in Madelung's disease may be extensive to involvement of arms, axillae, mediastinum (and may compromise airway); halting with EtOH intake
• Diffuse lipomatosis may cause bony hypertrophy
• Pelvic lipomatosis associated with hydronephrosis and uremia or GI obstruction
• Lumbosacral lipoma often (67%) associated with progressive radiculopathy (spina bifida and spinal cord lipoma)
• Lipoma involving the synovium (lipoma arborescens), if not extensive, has been reported to have been txd with arthroscopic resection (bilateral knee tx also reported)
• Tx is complete excision including synovium involved
• Rarely reported in hip
• Intraneural lipofibroma (lipofibromatous hamartoma) can be dissected free off fascicles with preservation of nerve function
  • Ulnar nerve involvement at the elbow reported
• Endoscopic resection of GI lipomas reported
  • Can be acccurately diagnosed with endoscopic US
• Laparoscopic resection of colonic lipomas reported 
• Malignant epithelioid hemangioendothelioma arising in an intramuscular lipoma has been reported

SPECIAL CONSIDERATIONS

• Multiple lipomas

• • (Superficial lesions)
  • Non-familial cases account for the majority of cases

• Multiple Familial Lipomas

• ? A

• Lipoma Arborescens

  • Intra-articular lipoma

    • Knee location
      • Reported with locking
      • Suggested that disease may be associated with a secondary response to degenerative arthritis

• Lipomatoses

• Encephalocraniocutaneous lipomatosis

  •  Compressive myeloradiculopathy reported from subpial (intramedullary) spinal lipoma in an infant

    •  Bilateral UE paralysis presentation

• Nevus Lipomatosis Superficialis

  • Developmental nevoid form of lipoma characterized by the ectopic presence of mature adipocytes in the reticular dermis

• Fibrolipoma 

• • Commonly occurs in the head/neck region (1-4% of lipomas)
    • 34.1% of lipomas in the oral cavity
      • (Others include lipoma [41.5%], spindle cell lipoma [9.8%], sialolipoma [9.8%], osteolipoma [2.4%], chondrolipoma [2.4%])
        • Presents as an asymptomatic, mobile swelling of soft consistency
      • Lip location has been reportedly treated by diode laser surgery
        • 300 ?m fiber operating at 2.5 W
    • Has been reported in association with a mucus retention cyst in the palate
    • Has been reported on the tip of the nose
    • Gastric fibrolipomareported causing melena in a 10-year-old
      • Gastroscopy revealed a soft, elevated, broad based, polypoid posterior wall lesion
      • Acute GI hemorrhage has also been reported
    • Giant UE fibrolipomas reported

  • Animal Model

    • Reported occuring in a retroparietal location in association with retroparietal osteochondroma in a calf

  • (Intra)Neural Fibrolipoma

• • • Fibrolipomatous hamartoma of the median nerve

• • • • Infiltration of the epineurium and perineurium with fibrofatty tissue
      • Involvement of bilateral median nerveshas been reported
        • Severe carpal tunnel syndrome reported to resolve with carpal tunnel release
      • Involvement of the ulnar nerve at the wrist reported
        • Surgical debulking with microsurgery reported with satisfactory results
      • Involvlement of the superficial peroneal nerveat the ankle reported
        • + CD34 in the fibrous spindle cells reported
      • Involvement of a digital nerve without macrodactyly reported
      • Involvement of multiple nerves in the wrist reported
      • Diffuse neck mass reported

  • Giant Fibrolipoma

• • • At least 10 cm in dia or weigh a minimum of 1000 g
    • CT
      • Heterogeneous enhancement reported
    • MRI
      • Heterogeneous enhancement reported
    • Giant fibrolipoma of the hypophyarynx reported
    • Giant fibrolipoma of the esophagus reported
      • Transoral surgical excision reported
    • Abdominal location reported to mimick abdominal lipodystrophy
    • Giant fibrolipoma of the spermatic cord reported
    • May be pedunculated
  • Unusual locations
    • Mediastinum location outside the esophagus reported
    • Subcutaneous upper back location reported
    • Ankle/heel location reported
    • Third toe location txd with amputation reported
      
      

  • Congenital Fibrolipoma

• • • Has been reported occurring in the anal canal 

• Bannayan-Zonana Syndrome

• • (Multiple lipomas, macrocephaly, hemangiomas)

• Cowden Syndrome

• • (Multiple lipomas, hemangiomas associated with goiter, skin and mucosal lichenoid lesions)

• Frohlich Syndrome

• • (Multiple lipomas, obesity, sexual infantilism)

• Proteus Syndrome

• • Harmartomatous condition characterized by patchy or segmental overgrowthand hyperplasia with susceptibi8lity to development of tumors
    • Hemagiomas
    • Lipomas
    • Lymphangiomas
    • Varicosities
    • Verrucous epidermal nevi
    • Macrocephaly
    • Cranial exostosis
  • Hemihypertrophy and overgrowth reported presenting from 2 months to 10 years
  • (Multiple lipomatous lesions, feet/hand fibroplasia, skeletal hypertrophy, exostoses, scoliosis, pigmented skin lesions)(other neoplasms have been reported)
  • Acetabular dysplasia associated with intra-articular lipomatous lesions has been reported
  • Joseph Carey Merrick (the Elephant Man), described by Treves is thought to have had this syndrome (not NF1)

• Spinal (Epidural) Lipoma, Spinal Angiomyolipoma, Spinal Angiolipoma

• • Usually related to steroid use
  • Neurological sxs vary depending on level involved
  • Mobilization off the compressed dura via laminectomies has been reported
  • May be due to venous thrombosis of the lesion
  • Extracanal extension into the posterior mediastinum has been reported
  • MRI diagnostic

• Spinal (Epidural) Lipomatosis

• • Rarely found without steroid use or endocrinopathy
  • Obesity nearly always reported in idiopathic cases
  • M>F
  • MRI diagnostic
  • Thoracic level most commonly affected
  • Complete resolution of sxs with weight reduction
  • Laminectomy and fat debulking successful but not without risks

   

• Spinal Cord Lipoma

•  

  •  Dorsal lipoma

    •  Lipoma–cord interface is entirely on the dorsal surface of the lumbar spinal cord, always sparing the distal conus lipoma

• Transitional lipoma

  • Plunges caudally to involve the conus

     

• Terminal lipoma

  • Insert into the caudal extremity of the conus without blending with the spinal cord or its root entry zones

     

• Chaotic lipoma

  • Begins dorsally as in a dorsal or transitional lipoma, but its caudal portion is ventral to the neural placode, engulfs neural tissue and nerve roots

     

     

     

• Spinal (Epidural) Angiolipoma

  • Spindle shaped located in the posterior epidural space

  • Fat and vascular elements on MR imaging (either may predominate: type 1 predominantly lipomatous; type 2 predominantly vascular)

    • Vascular content:

      • Hypointense regions on T1-weighted imaging
      • Hyperintense regions on T2-weighted imagin
      • Marked enhancement

         

    • Fat content:

    • •  Isointense with epidural fat

• Intravascular Lipoma

• • Superior vena cava location reported
    • Nonenhancing 9 X 5 cm tumor occluding R subclavian vein, brachiocephalic vein, and SVC to the R atrium reported on CT
    • MRI reported as isointense lesion with fat
    • PET reported with no fludeoxyglucose F 18 uptake
    • Surgical resection through combined median sternotomy and R transclavicular cervicotomy
      • Control of SVC, subclavian, internal jugular and azygos vein with this approach

  • Intracardiac Lipoma

• • • Commonest nonmyxomatous benign primary cardiac tumor
    • Lipoma arising from papillary muscle reported

• Angiolipoma

  • Unusual location

    • Buccal mucosa

• Angiofibrolipoma

  •  

    • Intranasal with nasal obstruction

• Angiomyxolipoma

  • Rare form of lipoma
  • Unusual location
    • Parapharyngeal space

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