1990 Rosati – Lipomi episacroiliaci

Notes on the article:

Article from 1990 written in Italian about lipomi episacroiliaci  (also known as back mice). They presented 21 cases that they successfully resolved by surgical excision. The authors want to remember the EXISTENCE of these lipomas related to low back pain syndromes that seem to have been neglected in the past 50 years.

They present a literature review about relevant works of the 50s (Copeman & Ackerman, Donati & Bidone, Herz, Hittner, Ries, Rosati & Nocentini, and Sicard & Lord).

They introduce the role of lumbar sonography to complement the diagnosis of the lipomi episacroiliaci.

They explain that the pain can be REMOVED by a SIMPLE surgical technique that they explain briefly.

Apparently, they do not mention that some patients may just have relief by just performing infiltrations (as other authors published).

After reviewing the literature and following his own experience the authors reach certain conclusions about the lipomi episacroiliaci:

 -They are NOT a rare clinical entity.

-It presents like a lumbosciatalgic syndrome that radiates to the lateral thigh.

-It can be confirmed by sonographic examination.

-Its surgical removal results in remission of pain.

-Regarding to the etiopathogenic mechanism: they mention that it would be a fat herniation through the lumbododorsal fascia. The fat normally exists in the deep subfascial layer. This tissue can undergo a process of lobulation and increasing volume or hyperplasia which would determinate the phenomenon of mass lobulation and other phenomena such as stasis, edema and hemorrhage.

-The close contact the masses have with the low back peripheral nerves (clunium craniales or cluneal nerves) would explain the pain symptomatology.

Il rulo dei lipomi episacroiliaci come causa di sindromi pseudolombosciatalgiche

[The role of the episacroiliac lipomas as a cause of pseudolombosciatalgic syndrome]

Rosati and D. Mariani

Divisione di ortopedia I. O. T. Firenze

The authors mention that the patients with lumbosciatic syndromes are frequent. Many have had instrumental examinations such as TC, RMN, EMG that DO NOT show signs of disc, bone or articular pathology.

But in some of them a careful physical examination reveals the presence of LIPOMATOSE FORMATIONS (lipomi episacroiliaci or back mice), usually of modest size, in the sacroiliac area.

In 1937 Ries had the merit to draw attention to these formations that he called episacroiliac lipomas, emphasizing their significance.

After Ries, other authors such as Copeman and Ackerman (1944), Hittner (1949), and Donati and Bidoni (1952) also published about these nodules.

UNFORTUNATELY, this clinical entity has been neglected, even forgotten in the differential diagnosis of the lumbosciatalgic syndromes.

About prevalence of the lipomi episacroiliaci

Regarding the incidence of the lumbosciatalgic syndrome related to these nodulations, the data from Ries is the most extended. He explored 1,000 patients and reported 317 cases. Rosati and Bidone and many other articles, although less extended, suggested that the entity IS NOT INFREQUENT.

They also mention that the studies suggested predominance of female cases (Ries (1937), Herz (1945), Hittner (1949), Sicard and Lord (1952), Donati and Bidoni (1952)). Ries reported 271 women versus 46 men from the 317 cases. Hittner published 36 female cases and 14 men cases.

About age, it seems it presents in the adult ages and especially in the 4th decade.

About localization and morphology of the lipomi episacroiliaci

lipomi episacroiliaci

  • They are found in an area proximal of the sacroiliac articulation.
  • They are often bilateral and symmetrical, roundish or ovoid with a smooth surface.
  • They are often multiple.
  • The volume varies from a hazelnut to a pigeon’s egg.
  • In some cases there exists a STALK (Herz and Copeman & Ackerman).
  • The consistency is usually soft and elastic, which sometimes may grow due to an increase of the presence of connective tissue.

Histology findings of the lipomi episacroiliaci

They usually present the characteristic areolar arrangement of adult adipose cells, sometimes with interstitial edema (Copeman) or focal hemorrhage (Herz). Hittner mentions a connective capsule with neoformations. There are blood vessels and nerve fibers and sometimes this suggested the authors to be a “neurolipoma” (Becke). Some others talk about a neurofibrilar net by staining with argent stain.

The etiopathogenesis of the lipomi episacroiliaci

-Campiglio (1950) related them to an endocrine-type mechanism.

-Bianchi (1952) related them to metabolic-protein imbalances.

-They have also been related to the fat herniation due to trauma (Copeman & Ackerman), which would lead to the symptoms.

-Copeman also related them to a dysfunction of the water metabolism that would cause edema of the fatty tissue. Then there would be distension within the capsule and compression of the intralipomatose nerve filaments.

-The radiation of pain had been related to the presence of the posterior branches of cutaneous nerves (cluneal nerves).

Nevertheless, the complete picture of the etiopathogenic factors is still obscure.

Rosati and Mariani describe anatomy of the region where the lipomi episacroiliaci are found

From the outside to the inside in the lower lumbar region, the following anatomical structures are found:


-Subcutaneous fat

-Leaflet of superficial fascia

-Deep subcutaneous tissue

-Deep fascia

lipomi episacroiliaci

The dorsal perpiheral nerve branches (cluneal nerves) cross the deep fascia at certain points through certain foramina. And then they give branches to innervate the surface. At the crossing foramina they could be affected by the lipomi episacroiliaci (Chiarugi & Bucciante, 1973).

Clinical picture of the lipomi episacroiliaci patients

Omitting the ASYMPTOMATIC forms, there are 2 main forms:

  • The lombosciatalgic forms
  • The lumbosacralgic forms

The lombosciatalgic form: It is characterized by irradiation of the pain to the leg, trochanteric region, lateral aspect of the thigh to the level of the knee, and never to the foot. The pain is of burning nature and it is accentuated with physical activity and sometimes with the supine position, and it reduces with rest and taking different positions.

lipomi episacroiliaci

There is a total absence of the sign of Lasègue and Wassermann, the patelar and Achilles reflexes are normal. There is no stiffness or painfulness of the spine.

The EMG shows no pathological results.

The only finding in examination is the tumefaction of the epsiacroiliac site. The masses can be painful on palpation in a recognizable way by the patient. And it can radiate.

The lumbosacralgic form: It is less frequent; there is a lumbosacral paravertebral irradiation.

Many times the patient is unaware of these formations.

Diagnosis of the lipomi episacroiliaci

  1. Presence in the episacroiliac area of a single or multiple swelling which, on palpation, is of soft elastic consistency, movable on deep planes. No inflammatory signs.
  2. Pain localized and irradiated to the thigh up to the knee (absence of the classic signs of Lasègue and Wassermann, normal reflexes, validity of the extensors muscles of the foot).
  3. Images of fatty tissue with sonographic examination (non invasive diagnosis)
  4. Disappearance of pain after infiltration of anesthetic (1% procaine) in the lipomi episacroiliaci. The diagnosis is most certain if the remission of the symptoms lasts longer than the time expected by the inherent action of the drug.
  5. Negative findings in the other classical instrumental exams: standard RX, radiculography, TC, RNM, and EMG.

lipomi episacroiliaci

Therapy of the lipomi episacroiliaci

The only therapeutic treatment is the surgical one. The infiltration has a more diagnostic than curative role, even that the remission of symptomatology can be for a long time.

The surgical removal can be unilateral or bilateral. After a transverse incision of 5 cm over the palpable mass.

In obese patients, the use of general anesthetic is sometimes necessary.

It is important to avoid hematoma by closing the residual cavity.

lipomi episacroiliaci

Casuistry of the lipomi episacroiliaci

  • They presented 21 cases, 5 men and 16 women. Aged between 20 to 61 years, with greater incidence in the fourth decade of life.
  • Pain on the episacroiliac region. On examination, 18 patients presented BILATERAL epoisacroiliac lipomas or lipomi episacroiliaci; the rest just unilateral ones.
  • All lipomas were formed by MULTILOBULATED adipose masses, of soft-elastic consistency, of various sizes (one reached the size of 10 cm and weighed 40 grs).
  • Usually the symptomatology arose SLOWLY for months or years.
  • Usually pain was constantly irradiated to lateral thigh.
  • The injection of local anesthetic meant a powerful diagnostic tool to them.
  • They also confirm their suspicions by sonography of the masses.
  • The authors are aware that no previous studies did a sonography to complete the diagnosis.
  • The histological findings informed: “Mature lipoma in all sections”.
  • The remission of pain was in general rapid and without recurrences within one year.

Published in July 2018 by Marta Cañis Parera    ORCID iD icon


Rosati E, Mariani D. [The role of episacroiliac lipomas as a cause of pseudolumbago-sciatica syndromes]. Arch Putti Chir Organi Mov. 1990;38(2):339-47. Review. Italian. PubMed PMID: 2151647.

Copeman WSC. Fibro-fatty Tissue and its Relation to “Rheumatic” Syndromes. British Medical Journal. 1949;2(4620):191-197.

R HERZ. HERNIATION OF FASCIAL FAT AS A CAUSE OF LOW BACK PAINWITH RELIEF BY SURGERY IN SIX CASES. 1945;128(13):921–925. doi:10.1001/jama.1945.02860300011003.

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Ries E. Episacroiliac lipomaAm J Obstet Gynecol 1937;34:492-8.

NOCENTINI P, ROSATI I. [Anatomicoclinical picture of episacroiliac lipomas]. Acta Chir Ital. 1956;12(3):345-80. Italian. PubMed PMID: 13372094.

SICARD A, LORD G. [Episacroiliac lipomas and lumbo-sciatica]. Presse Med. 1952 Jul 26;60(50):1073-4. Undetermined Language. PubMed PMID: 13026891.